diff --git a/src/batch-transaction.ts b/src/batch-transaction.ts
index 2b1d979da..cfee7f974 100644
--- a/src/batch-transaction.ts
+++ b/src/batch-transaction.ts
@@ -119,9 +119,7 @@ class BatchTransaction extends Transaction {
     }
     const reqOpts = codec.encodeQuery(query);
     const gaxOpts = query.gaxOptions;
-    if (gaxOpts) {
-      delete reqOpts.gaxOptions;
-    }
+
     this.createPartitions_(
         {
           client: 'SpannerClient',
@@ -194,9 +192,7 @@ class BatchTransaction extends Transaction {
   createReadPartitions(options, callback) {
     const reqOpts = codec.encodeRead(options);
     const gaxOpts = options.gaxOptions;
-    if (gaxOpts) {
-      delete reqOpts.gaxOptions;
-    }
+
     this.createPartitions_(
         {
           client: 'SpannerClient',
diff --git a/src/codec.ts b/src/codec.ts
index 56d3bcdc4..c81a48d62 100644
--- a/src/codec.ts
+++ b/src/codec.ts
@@ -13,15 +13,45 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-
 import {Service} from '@google-cloud/common-grpc';
 import * as arrify from 'arrify';
-import * as extend from 'extend';
+import {CallOptions} from 'google-gax';
 import * as is from 'is';
+import {common as p} from 'protobufjs';
+
+import {SpannerClient as s} from './v1';
+
+// tslint:disable-next-line no-any
+type Value = any;
+
+interface Field {
+  name: string;
+  value: Value;
+}
+
+interface Json {
+  [field: string]: Value;
+}
+
+/**
+ * @typedef JsonOptions
+ * @property {boolean} [wrapNumbers=false] Indicates if the numbers should be
+ *     wrapped in Int/Float wrappers.
+ * @property {boolean} [wrapStructs=false] Indicates if the structs should be
+ *     wrapped in Struct wrapper.
+ */
+interface JsonOptions {
+  wrapNumbers?: boolean;
+  wrapStructs?: boolean;
+}
 
+/**
+ * @typedef SpannerDate
+ * @see Spanner.date
+ */
 export class SpannerDate {
-  value;
-  constructor(value) {
+  value: string;
+  constructor(value?: string|number|Date) {
     if (arguments.length > 1) {
       throw new TypeError([
         'The spanner.date function accepts a Date object or a',
@@ -31,156 +61,162 @@ export class SpannerDate {
     if (is.undefined(value)) {
       value = new Date();
     }
-    this.value = new Date(value).toJSON().replace(/T.+/, '');
+    this.value = new Date(value!).toJSON().replace(/T.+/, '');
   }
 }
 
-export class Float {
-  value;
-  constructor(value) {
+/**
+ * Using an abstract class to simplify checking for wrapped numbers.
+ *
+ * @private
+ */
+abstract class WrappedNumber {
+  value!: string|number;
+  abstract valueOf(): number;
+}
+
+/**
+ * @typedef Float
+ * @see Spanner.float
+ */
+export class Float extends WrappedNumber {
+  value: number;
+  constructor(value: number) {
+    super();
     this.value = value;
   }
-  valueOf() {
+  valueOf(): number {
     return Number(this.value);
   }
 }
 
-export class Int {
-  value;
-  constructor(value) {
+/**
+ * @typedef Int
+ * @see Spanner.int
+ */
+export class Int extends WrappedNumber {
+  value: string;
+  constructor(value: string) {
+    super();
     this.value = value.toString();
   }
-  valueOf() {
+  valueOf(): number {
     const num = Number(this.value);
     if (num > Number.MAX_SAFE_INTEGER) {
-      throw new Error('Integer ' + this.value + ' is out of bounds.');
+      throw new Error(`Integer ${this.value} is out of bounds.`);
     }
     return num;
   }
 }
 
 /**
- * We use this symbol as a means to identify if an array is actually a struct.
- * We need to do this because changing Structs from an object to an array would
- * be a major breaking change.
- *
- * @private
- *
- * @example
- * const struct = [];
- * struct[TYPE] = 'struct';
- */
-const TYPE = Symbol();
-
-/**
- * Struct wrapper. This returns an array, but will decorate the array to give it
- * struct characteristics.
- *
- * @private
- *
- * @returns {array}
+ * @typedef Struct
+ * @see Spanner.struct
  */
-export class Struct extends Array {
-  constructor() {
-    super();
-    this[TYPE] = Struct.TYPE;
-    Object.defineProperty(
-        this, 'toJSON',
-        {enumerable: false, value: codec.generateToJSONFromRow(this)});
-  }
-
+export class Struct extends Array<Field> {
   /**
-   * Use this to assign/check the type when dealing with structs.
+   * Converts struct into a pojo (plain old JavaScript object).
    *
-   * @private
+   * @param {JsonOptions} [options] JSON options.
+   * @returns {object}
    */
-  static TYPE = 'struct';
-
+  toJSON(options?: JsonOptions): Json {
+    return codec.convertFieldsToJson(this, options);
+  }
   /**
-   * Converts an array of objects to a struct array.
+   * Converts an array of fields to a struct.
    *
    * @private
    *
-   * @param {object[]} arr Struct array.
+   * @param {object[]} fields List of struct fields.
    * @return {Struct}
    */
-  static fromArray(arr) {
-    const struct = new Struct();
-    struct.push.apply(struct, arr);
-    return struct;
+  static fromArray(fields: Field[]): Struct {
+    return new Struct(...fields);
   }
-
   /**
-   * Converts a JSON object to a struct array.
+   * Converts a JSON object to a struct.
    *
    * @private
    *
    * @param {object} json Struct JSON.
    * @return {Struct}
    */
-  static fromJSON(json: {}) {
-    const struct = new Struct();
-    Object.keys(json || {}).forEach(name => {
+  static fromJSON(json: Json): Struct {
+    const fields = Object.keys(json || {}).map(name => {
       const value = json[name];
-      struct.push({name, value});
+      return {name, value};
     });
-    return struct;
+    return Struct.fromArray(fields);
   }
+}
 
-  /**
-   * Checks to see if the provided object is a Struct.
-   *
-   * @private
-   *
-   * @param {*} thing The object to check.
-   * @returns {boolean}
-   */
-  static isStruct(thing: {}): thing is Struct {
-    return !!(thing && thing[TYPE] === Struct.TYPE);
+/**
+ * Wherever a row or struct object is returned, it is assigned a "toJSON"
+ * function. This function will generate the JSON for that row.
+ *
+ * @private
+ *
+ * @param {array} row The row to generate JSON for.
+ * @param {JsonOptions} [options] JSON options.
+ * @returns {object}
+ */
+function convertFieldsToJson(fields: Field[], options?: JsonOptions): Json {
+  const json: Json = {};
+
+  const defaultOptions = {wrapNumbers: false, wrapStructs: false};
+
+  options = Object.assign(defaultOptions, options);
+
+  for (const {name, value} of fields) {
+    if (!name) {
+      continue;
+    }
+
+    try {
+      json[name] = convertValueToJson(value, options);
+    } catch (e) {
+      e.message = [
+        `Serializing column "${name}" encountered an error: ${e.message}`,
+        'Call row.toJSON({ wrapNumbers: true }) to receive a custom type.',
+      ].join(' ');
+      throw e;
+    }
   }
+
+  return json;
 }
 
 /**
- * Wherever a row object is returned, it is assigned a "toJSON" function. This
- * function will create that function in a consistent format.
+ * Attempts to convert a wrapped or nested value into a native JavaScript type.
  *
- * @param {array} row The row to generate JSON for.
- * @returns {function}
+ * @private
+ *
+ * @param {*} value The value to convert.
+ * @param {JsonOptions} options JSON options.
+ * @return {*}
  */
-function generateToJSONFromRow(row) {
-  return (options) => {
-    options = extend(
-        {
-          wrapNumbers: false,
-        },
-        options);
-
-    return row.reduce((serializedRow, keyVal) => {
-      const name = keyVal.name;
-      let value = keyVal.value;
-
-      if (!name) {
-        return serializedRow;
-      }
+function convertValueToJson(value: Value, options: JsonOptions): Value {
+  if (!options.wrapNumbers && value instanceof WrappedNumber) {
+    return value.valueOf();
+  }
 
-      const isNumber = value instanceof Float || value instanceof Int;
-      if (!options.wrapNumbers && isNumber) {
-        try {
-          value = value.valueOf();
-        } catch (e) {
-          e.message = [
-            `Serializing column "${name}" encountered an error: ${e.message}`,
-            'Call row.toJSON({ wrapNumbers: true }) to receive a custom type.',
-          ].join(' ');
-          throw e;
-        }
-      }
+  if (value instanceof Struct) {
+    if (!options.wrapStructs) {
+      return value.toJSON(options);
+    }
 
-      serializedRow[name] = value;
+    return value.map(({name, value}) => {
+      value = convertValueToJson(value, options);
+      return {name, value};
+    });
+  }
 
-      return serializedRow;
-    }, {});
-  };
+  if (Array.isArray(value)) {
+    return value.map(child => convertValueToJson(child, options));
+  }
+
+  return value;
 }
 
 /**
@@ -189,53 +225,47 @@ function generateToJSONFromRow(row) {
  * @private
  *
  * @param {*} value Value to decode
- * @param {object[]} field Struct fields
+ * @param {object[]} type Value type object.
  * @returns {*}
  */
-function decode(value, field) {
-  function decodeValue_(decoded, type) {
-    if (is.null(decoded)) {
-      return null;
-    }
-    switch (type.code) {
-      case 'BYTES':
-        decoded = Buffer.from(decoded, 'base64');
-        break;
-      case 'FLOAT64':
-        decoded = new codec.Float(decoded);
-        break;
-      case 'INT64':
-        decoded = new codec.Int(decoded);
-        break;
-      case 'TIMESTAMP':  // falls through
-      case 'DATE':
-        decoded = new Date(decoded);
-        break;
-      case 'ARRAY':
-        decoded = decoded.map(value => {
-          return decodeValue_(value, type.arrayElementType);
-        });
-        break;
-      case 'STRUCT':
-        // tslint:disable-next-line no-any
-        const struct = new (Struct as any)();
-        const fields = type.structType.fields;
-        fields.forEach((field, index) => {
-          const name = field.name;
-          let value = decoded[name] || decoded[index];
-          value = decodeValue_(value, field.type);
-          struct.push({name, value});
-        });
-        decoded = struct;
-        break;
-      default:
-        break;
-    }
+function decode(value: Value, type: s.Type): Value {
+  if (is.null(value)) {
+    return null;
+  }
 
-    return decoded;
+  let decoded = value;
+
+  switch (type.code) {
+    case s.TypeCode.BYTES:
+      decoded = Buffer.from(decoded, 'base64');
+      break;
+    case s.TypeCode.FLOAT64:
+      decoded = new Float(decoded);
+      break;
+    case s.TypeCode.INT64:
+      decoded = new Int(decoded);
+      break;
+    case s.TypeCode.TIMESTAMP:  // falls through
+    case s.TypeCode.DATE:
+      decoded = new Date(decoded);
+      break;
+    case s.TypeCode.ARRAY:
+      decoded = decoded.map(value => {
+        return decode(value, type.arrayElementType!);
+      });
+      break;
+    case s.TypeCode.STRUCT:
+      const fields = type.structType!.fields.map(({name, type}, index) => {
+        const value = decode(decoded[name] || decoded[index], type!);
+        return {name, value};
+      });
+      decoded = Struct.fromArray(fields);
+      break;
+    default:
+      break;
   }
 
-  return decodeValue_(value, field.type);
+  return decoded;
 }
 
 /**
@@ -243,108 +273,144 @@ function decode(value, field) {
  *
  * @private
  *
- * @param {*} value The value to be encoded
+ * @param {*} value The value to be encoded.
+ * @returns {object} google.protobuf.Value
+ */
+function encode(value: Value): p.IValue {
+  return Service.encodeValue_(encodeValue(value));
+}
+
+/**
+ * Formats values into expected format of google.protobuf.Value. The actual
+ * conversion to a google.protobuf.Value object happens via
+ * `Service.encodeValue_`
+ *
+ * @private
+ *
+ * @param {*} value The value to be encoded.
  * @returns {*}
  */
-function encode(value) {
-  function preEncode(value) {
-    const numberShouldBeStringified =
-        (!(value instanceof Float) && is.integer(value)) ||
-        value instanceof Int || is.infinite(value) || Number.isNaN(value);
-
-    if (is.date(value)) {
-      value = value.toJSON();
-    } else if (
-        value instanceof SpannerDate || value instanceof Float ||
-        value instanceof Int) {
-      value = value.value;
-    } else if (Buffer.isBuffer(value)) {
-      value = value.toString('base64');
-    } else if (Struct.isStruct(value)) {
-      value = value.map(field => preEncode(field.value));
-    } else if (is.array(value)) {
-      value = value.map(preEncode);
-    } else if (is.object(value) && is.fn(value.hasOwnProperty)) {
-      for (const prop in value) {
-        if (value.hasOwnProperty(prop)) {
-          value[prop] = preEncode(value[prop]);
-        }
-      }
-    }
+function encodeValue(value: Value): Value {
+  if (is.number(value) && !is.decimal(value)) {
+    return value.toString();
+  }
 
-    if (numberShouldBeStringified) {
-      value = value.toString();
-    }
+  if (is.date(value)) {
+    return value.toJSON();
+  }
+
+  if (value instanceof WrappedNumber || value instanceof SpannerDate) {
+    return value.value;
+  }
+
+  if (Buffer.isBuffer(value)) {
+    return value.toString('base64');
+  }
 
-    return value;
+  if (value instanceof Struct) {
+    return Array.from(value).map(field => encodeValue(field.value));
   }
-  // tslint:disable-next-line no-any
-  return (Service as any).encodeValue_(preEncode(value));
+
+  if (is.array(value)) {
+    return value.map(encodeValue);
+  }
+
+  return value;
+}
+
+/**
+ * Just a map with friendlier names for the types.
+ *
+ * @private
+ * @enum {string}
+ */
+enum TypeCode {
+  unspecified = s.TypeCode.TYPE_CODE_UNSPECIFIED,
+  bool = s.TypeCode.BOOL,
+  int64 = s.TypeCode.INT64,
+  float64 = s.TypeCode.FLOAT64,
+  timestamp = s.TypeCode.TIMESTAMP,
+  date = s.TypeCode.DATE,
+  string = s.TypeCode.STRING,
+  bytes = s.TypeCode.BYTES,
+  array = s.TypeCode.ARRAY,
+  struct = s.TypeCode.STRUCT
+}
+
+/**
+ * Conveniece Type object that simplifies specifying the data type, the array
+ * child type and/or struct fields.
+ *
+ * @private
+ */
+interface Type {
+  type: string;
+  fields?: FieldType[];
+  child?: Type;
+}
+
+interface FieldType extends Type {
+  name: string;
 }
 
 /**
- * Get the corresponding Spanner data type.
+ * Get the corresponding Spanner data type for the provided value.
  *
  * @private
  *
- * @param {*} field - The field value.
- * @returns {string}
+ * @param {*} value - The value.
+ * @returns {object}
  *
  * @example
- * Database.getType_(NaN);
- * // 'float64'
+ * codec.getType(NaN);
+ * // {type: 'float64'}
  */
-function getType(field) {
-  if (is.boolean(field)) {
-    return 'bool';
-  }
-
-  const isSpecialNumber = is.infinite(field) ||
-      (is.number(field) && isNaN(field));
+function getType(value: Value): Type {
+  const isSpecialNumber = is.infinite(value) ||
+      (is.number(value) && isNaN(value));
 
-  if (is.decimal(field) || isSpecialNumber || field instanceof Float) {
-    return 'float64';
+  if (is.decimal(value) || isSpecialNumber || value instanceof Float) {
+    return {type: 'float64'};
   }
 
-  if (is.number(field) || field instanceof Int) {
-    return 'int64';
+  if (is.number(value) || value instanceof Int) {
+    return {type: 'int64'};
   }
 
-  if (is.string(field)) {
-    return 'string';
+  if (is.boolean(value)) {
+    return {type: 'bool'};
   }
 
-  if (Buffer.isBuffer(field)) {
-    return 'bytes';
+  if (is.string(value)) {
+    return {type: 'string'};
   }
 
-  if (is.date(field)) {
-    return 'timestamp';
+  if (Buffer.isBuffer(value)) {
+    return {type: 'bytes'};
   }
 
-  if (field instanceof SpannerDate) {
-    return 'date';
+  if (is.date(value)) {
+    return {type: 'timestamp'};
   }
 
-  if (Struct.isStruct(field)) {
-    const fields = field.map(field => {
-      return {
-        name: field.name,
-        type: getType(field.value),
-      };
-    });
+  if (value instanceof SpannerDate) {
+    return {type: 'date'};
+  }
 
+  if (value instanceof Struct) {
     return {
       type: 'struct',
-      fields,
+      fields: Array.from(value).map(({name, value}) => {
+        return Object.assign({name}, getType(value));
+      }),
     };
   }
 
-  if (is.array(field)) {
+  if (is.array(value)) {
     let child;
 
-    for (let i = 0; i < field.length; i++) {
-      child = field[i];
+    for (let i = 0; i < value.length; i++) {
+      child = value[i];
 
       if (!is.null(child)) {
         break;
@@ -357,40 +423,51 @@ function getType(field) {
     };
   }
 
-  return 'unspecified';
+  return {type: 'unspecified'};
 }
 
 /**
- * A list of available Spanner types. The index of said type in Array aligns
- * with the type code that query params require.
+ * Generic request options.
  *
  * @private
  */
-const TYPES = [
-  'unspecified',
-  'bool',
-  'int64',
-  'float64',
-  'timestamp',
-  'date',
-  'string',
-  'bytes',
-  'array',
-  'struct',
-];
+interface RequestOptions {
+  json?: boolean;
+  jsonOptions?: JsonOptions;
+  gaxOptions?: CallOptions;
+}
+
+/**
+ * ExecuteSql request options. This includes all standard ExecuteSqlRequest
+ * options as well as several convenience properties.
+ *
+ * @see [Query Syntax](https://cloud.google.com/spanner/docs/query-syntax)
+ * @see [ExecuteSql API Documentation](https://cloud.google.com/spanner/docs/reference/rpc/google.spanner.v1#google.spanner.v1.Spanner.ExecuteSql)
+ *
+ * @typedef ExecuteSqlRequest
+ * @property {object} [params] A map of parameter names to values.
+ * @property {object} [types] A map of parameter names to types. If omitted the
+ *     client will attempt to guess for all non-null values.
+ * @property {boolean} [json=false] Receive the rows as serialized objects. This
+ *     is the equivalent of calling `toJSON()` on each row.
+ * @property {JsonOptions} [jsonOptions] Configuration options for the
+ *     serialized objects.
+ */
+export interface ExecuteSqlRequest extends s.ExecuteSqlRequest, RequestOptions {
+  params?: {[field: string]: Value};
+  types?: {[field: string]: string|Type};
+}
 
 /**
  * Encodes a ExecuteSqlRequest object into the correct format.
  *
  * @private
  *
- * @param {object} query The query object.
- * @param {object} [query.params] A map of parameter name to values.
- * @param {object} [query.types] A map of parameter types.
+ * @param {ExecuteSqlRequest} query The request object.
  * @returns {object}
  */
-function encodeQuery(query) {
-  query = extend({}, query);
+function encodeQuery(query: ExecuteSqlRequest): s.ExecuteSqlRequest {
+  query = Object.assign({}, query);
 
   if (query.params) {
     const fields = {};
@@ -399,77 +476,151 @@ function encodeQuery(query) {
       query.types = {};
     }
 
-    // tslint:disable-next-line forin
-    for (const prop in query.params) {
-      const field = query.params[prop];
-      if (!query.types[prop]) {
-        query.types[prop] = codec.getType(field);
+    const types = query.types!;
+
+    Object.keys(query.params).forEach(param => {
+      const value = query.params![param];
+      if (!types[param]) {
+        types[param] = codec.getType(value);
       }
-      fields[prop] = codec.encode(field);
-    }
+      fields[param] = codec.encode(value);
+    });
 
     query.params = {fields};
   }
 
   if (query.types) {
-    const formattedTypes = {};
-    // tslint:disable-next-line forin
-    for (const field in query.types) {
-      formattedTypes[field] = codec.createTypeObject(query.types[field]);
-    }
+    const paramTypes = {};
+
+    Object.keys(query.types).forEach(param => {
+      paramTypes[param] = codec.createTypeObject(query.types![param]);
+    });
+
+    query.paramTypes = paramTypes;
     delete query.types;
-    query.paramTypes = formattedTypes;
+  }
+
+  if (query.json) {
+    delete query.json;
+    delete query.jsonOptions;
+  }
+
+  if (query.gaxOptions) {
+    delete query.gaxOptions;
   }
 
   return query;
 }
 
+/**
+ * A KeyRange represents a range of rows in a table or index.
+ *
+ * A range has a start key and an end key. These keys can be open or closed,
+ * indicating if the range includes rows with that key.
+ *
+ * Keys are represented by an array of strings where the nth value in the list
+ * corresponds to the nth component of the table or index primary key.
+ *
+ * @typedef KeyRange
+ * @property {string[]} [startClosed] If the start is closed, then the range
+ *     includes all rows whose first key columns exactly match.
+ * @property {string[]} [startOpen] If the start is open, then the range
+ *     excludes rows whose first key columns exactly match.
+ * @property {string[]} [endClosed] If the end is closed, then the range
+ *     includes all rows whose first key columns exactly match.
+ * @property {string[]} [endOpen] If the end is open, then the range excludes
+ *     rows whose first key columns exactly match.
+ */
+interface KeyRange {
+  startClosed?: Value[];
+  startOpen?: Value[];
+  endClosed?: Value[];
+  endOpen?: Value[];
+}
+
+/**
+ * Read request options. This includes all standard ReadRequest options as well
+ * as several convenience properties.
+ *
+ * @see [StreamingRead API Documentation](https://cloud.google.com/spanner/docs/reference/rpc/google.spanner.v1#google.spanner.v1.Spanner.StreamingRead)
+ * @see [ReadRequest API Documentation](https://cloud.google.com/spanner/docs/reference/rpc/google.spanner.v1#google.spanner.v1.ReadRequest)
+ *
+ * @typedef ReadRequest
+ * @property {string[]} [keys] The primary keys of the rows in this table to be
+ *     yielded. If using a composite key, provide an array within this array.
+ *     See the example below.
+ * @property {KeyRange[]} [ranges] An alternative to the keys property, this can
+ *       be used to define a range of keys to be yielded.
+ * @property {boolean} [json=false] Receive the rows as serialized objects. This
+ *     is the equivalent of calling `toJSON()` on each row.
+ * @property {JsonOptions} [jsonOptions] Configuration options for the
+ *     serialized objects.
+ */
+export interface ReadRequest extends s.ReadRequest, RequestOptions {
+  keys?: string[];
+  ranges?: KeyRange[];
+}
+
 /**
  * Encodes a ReadRequest into the correct format.
  *
  * @private
  *
- * @param {object|string|string[]} query The query
+ * @param {ReadRequest} query The query
  * @returns {object}
  */
-function encodeRead(query) {
-  if (is.array(query) || is.string(query)) {
-    query = {
-      keys: query,
-    };
-  }
+export function encodeRead(query: ReadRequest): s.ReadRequest {
+  query = Object.assign({}, query);
 
-  const encoded = extend({}, query);
+  if (!query.keySet) {
+    query.keySet = {};
 
-  if (query.keys || query.ranges) {
-    encoded.keySet = {};
+    if (!query.keys && !query.ranges) {
+      query.keySet.all = true;
+    }
   }
 
   if (query.keys) {
-    encoded.keySet.keys = arrify(query.keys).map(key => {
-      return {
-        values: arrify(key).map(codec.encode),
-      };
-    });
-    delete encoded.keys;
+    query.keySet.keys = arrify(query.keys).map(convertToListValue);
+    delete query.keys;
   }
 
   if (query.ranges) {
-    encoded.keySet.ranges = arrify(query.ranges).map(rawRange => {
-      const range = extend({}, rawRange);
-      // tslint:disable-next-line forin
-      for (const bound in range) {
-        range[bound] = {
-          values: arrify(range[bound]).map(codec.encode),
-        };
-      }
+    query.keySet.ranges = arrify(query.ranges).map(keyRange => {
+      const range: s.KeyRange = {};
+
+      Object.keys(keyRange).forEach(bound => {
+        range[bound] = convertToListValue(keyRange[bound]);
+      });
 
       return range;
     });
-    delete encoded.ranges;
+    delete query.ranges;
+  }
+
+  if (query.json) {
+    delete query.json;
+    delete query.jsonOptions;
   }
 
-  return encoded;
+  if (query.gaxOptions) {
+    delete query.gaxOptions;
+  }
+
+  return query;
+}
+
+/**
+ * Converts a value to google.protobuf.ListValue
+ *
+ * @private
+ *
+ * @param {*} value The value to convert.
+ * @returns {object}
+ */
+function convertToListValue<T>(value: T): p.IListValue {
+  const values = arrify(value).map(codec.encode);
+  return {values};
 }
 
 /**
@@ -480,40 +631,32 @@ function encodeRead(query) {
  * @param {object|string} [config='unspecified'] Type config.
  * @return {object}
  */
-function createTypeObject(config) {
-  config = config || 'unspecified';
-
-  if (is.string(config)) {
-    config = {type: config};
+function createTypeObject(friendlyType?: string|Type): s.Type {
+  if (!friendlyType) {
+    friendlyType = 'unspecified';
   }
 
-  const type = config.type;
-  let code = TYPES.indexOf(type);
-
-  if (code === -1) {
-    code = 0;  // unspecified
+  if (is.string(friendlyType)) {
+    friendlyType = {type: friendlyType} as Type;
   }
 
-  // tslint:disable-next-line no-any
-  const typeObject: any = {code};
+  const config: Type = (friendlyType as Type);
+  const code: s.TypeCode = TypeCode[config.type] || TypeCode.unspecified;
+  const type: s.Type = {code};
 
-  if (type === 'array') {
-    typeObject.arrayElementType = createTypeObject(config.child);
+  if (code === s.TypeCode.ARRAY) {
+    type.arrayElementType = codec.createTypeObject(config.child);
   }
 
-  if (type === 'struct') {
-    typeObject.structType = {};
-    typeObject.structType.fields = arrify(config.fields).map(field => {
-      const fieldConfig = is.object(field.type) ? field.type : field;
-
-      return {
-        name: field.name,
-        type: createTypeObject(fieldConfig),
-      };
-    });
+  if (code === s.TypeCode.STRUCT) {
+    type.structType = {
+      fields: arrify(config.fields).map(field => {
+        return {name: field.name, type: codec.createTypeObject(field)};
+      })
+    };
   }
 
-  return typeObject;
+  return type;
 }
 
 export const codec = {
@@ -521,13 +664,11 @@ export const codec = {
   SpannerDate,
   Float,
   Int,
-  TYPE,
-  generateToJSONFromRow,
+  convertFieldsToJson,
   decode,
   encode,
   getType,
   encodeQuery,
-  TYPES,
   encodeRead,
   Struct
 };
diff --git a/src/database.ts b/src/database.ts
index 9012129d4..7c4ff8d7c 100644
--- a/src/database.ts
+++ b/src/database.ts
@@ -1332,8 +1332,7 @@ class Database extends ServiceObject {
           },
         };
       }
-      delete reqOpts.json;
-      delete reqOpts.jsonOptions;
+
       function makeRequest(resumeToken) {
         return self.makePooledStreamingRequest_({
           client: 'SpannerClient',
diff --git a/src/row-builder.ts b/src/row-builder.ts
index c20a27f81..cfd319239 100644
--- a/src/row-builder.ts
+++ b/src/row-builder.ts
@@ -113,12 +113,12 @@ class RowBuilder {
         const field = this.fields[index];
         return {
           name: field.name,
-          value: RowBuilder.formatValue(field, value),
+          value: codec.decode(value, field.type),
         };
       });
       Object.defineProperty(formattedRow, 'toJSON', {
         enumerable: false,
-        value: codec.generateToJSONFromRow(formattedRow),
+        value: options => codec.convertFieldsToJson(formattedRow, options),
       });
       return formattedRow;
     });
@@ -140,31 +140,6 @@ class RowBuilder {
     }
     return value;
   }
-  /**
-   * Format a value into the expected structure, e.g. turn struct values into an
-   * object.
-   *
-   * @param {object} field Field object
-   * @param {*} value Field value
-   * @returns {*}
-   */
-  static formatValue(field, value) {
-    if (value === 'NULL_VALUE') {
-      return null;
-    }
-    if (field.code === 'ARRAY') {
-      return value.map(value => {
-        return RowBuilder.formatValue(field.arrayElementType, value);
-      });
-    }
-    if (field.code !== 'STRUCT') {
-      return codec.decode(value, field);
-    }
-    return field.structType.fields.reduce((struct, field, index) => {
-      struct[field.name] = RowBuilder.formatValue(field, value[index]);
-      return struct;
-    }, {});
-  }
   /**
    * Merge chunk values.
    *
diff --git a/src/transaction-request.ts b/src/transaction-request.ts
index e0b1bc1e5..dc5649db7 100644
--- a/src/transaction-request.ts
+++ b/src/transaction-request.ts
@@ -209,18 +209,16 @@ class TransactionRequest {
    */
   createReadStream(table, query) {
     const reqOpts = codec.encodeRead(query);
+    const gaxOptions = query.gaxOptions;
+
     reqOpts.table = table;
-    delete reqOpts.json;
-    delete reqOpts.jsonOptions;
+
     if (this.transaction && this.id) {
       reqOpts.transaction = {
         id: this.id,
       };
     }
-    const gaxOptions = query.gaxOptions;
-    if (gaxOptions) {
-      delete reqOpts.gaxOptions;
-    }
+
     const makeRequest = resumeToken => {
       return this.requestStream({
         client: 'SpannerClient',
diff --git a/src/transaction.ts b/src/transaction.ts
index 422e1c554..208970825 100644
--- a/src/transaction.ts
+++ b/src/transaction.ts
@@ -724,9 +724,6 @@ class Transaction extends TransactionRequest {
         },
         codec.encodeQuery(query));
 
-    delete reqOpts.json;
-    delete reqOpts.jsonOptions;
-
     if (this.id) {
       reqOpts.transaction.id = this.id;
     } else {
diff --git a/src/v1/spanner_client.d.ts b/src/v1/spanner_client.d.ts
index e2fc13ebc..4d02bfac8 100644
--- a/src/v1/spanner_client.d.ts
+++ b/src/v1/spanner_client.d.ts
@@ -167,7 +167,7 @@ declare namespace SpannerClient {
     transaction?: TransactionSelector;
     sql: string;
     params?: protobuf.IStruct;
-    paramTypes: Array<[string, Type]>;
+    paramTypes?: {[field: string]: Type};
     resumeToken: Uint8Array | string;
     queryMode: QueryMode;
     partitionToken: Uint8Array | string;
@@ -219,12 +219,12 @@ declare namespace SpannerClient {
     session: string;
     transaction?: TransactionSelector;
     table: string;
-    index: string;
-    columns: string[];
-    keySet?: KeySet;
-    limit: number;
-    resumeToken: Uint8Array | string;
-    partitionToken: Uint8Array | string;
+    index?: string;
+    columns?: string[];
+    keySet: KeySet;
+    limit?: number;
+    resumeToken?: Uint8Array | string;
+    partitionToken?: Uint8Array | string;
   }
 
   interface ReadCallback {
@@ -272,9 +272,9 @@ declare namespace SpannerClient {
   }
 
   interface KeySet {
-    keys: protobuf.IListValue[];
-    ranges: KeyRange[];
-    all: boolean;
+    keys?: protobuf.IListValue[];
+    ranges?: KeyRange[];
+    all?: boolean;
   }
 
   interface Write {
@@ -375,21 +375,21 @@ declare namespace SpannerClient {
 
   interface TransactionSelector {
     singleUse?: TransactionOptions;
-    id: Uint8Array | string;
+    id?: Uint8Array | string;
     begin?: TransactionOptions;
   }
 
-  enum TypeCode {
-    TYPE_CODE_UNSPECIFIED,
-    BOOL,
-    INT64,
-    FLOAT64,
-    TIMESTAMP,
-    DATE,
-    STRING,
-    BYTES,
-    ARRAY,
-    STRUCT
+  const enum TypeCode {
+    TYPE_CODE_UNSPECIFIED = 'TYPE_CODE_UNSPECIFIED',
+    BOOL = 'BOOL',
+    INT64 = 'INT64',
+    FLOAT64 = 'FLOAT64',
+    TIMESTAMP = 'TIMESTAMP',
+    DATE = 'DATE',
+    STRING = 'STRING',
+    BYTES = 'BYTES',
+    ARRAY = 'ARRAY',
+    STRUCT = 'STRUCT'
   }
 
   interface Type {
diff --git a/system-test/spanner.ts b/system-test/spanner.ts
index 76d046228..2cfe25204 100644
--- a/system-test/spanner.ts
+++ b/system-test/spanner.ts
@@ -164,10 +164,6 @@ describe('Spanner', () => {
         database.run(query, (err, rows) => {
           assert.ifError(err);
 
-          const symbols = Object.getOwnPropertySymbols(rows[0][0].value[0]);
-          assert.strictEqual(symbols.length, 1);
-          assert.strictEqual(rows[0][0].value[0][symbols[0]], 'struct');
-
           const expected = [
             {
               name: '',
@@ -206,10 +202,6 @@ describe('Spanner', () => {
         database.run(query, (err, rows) => {
           assert.ifError(err);
 
-          const symbols = Object.getOwnPropertySymbols(rows[0][1].value[0]);
-          assert.strictEqual(symbols.length, 1);
-          assert.strictEqual(rows[0][1].value[0][symbols[0]], 'struct');
-
           const expected = [
             {
               name: 'id',
@@ -328,8 +320,9 @@ describe('Spanner', () => {
 
         insert({IntValue: value}, (err, row) => {
           assert.ifError(err);
-          const intValue = row.toJSON({wrapNumbers: true}).IntValue.value;
-          assert.strictEqual(intValue, value);
+          const expected = Spanner.int(value);
+          const actual = row.toJSON({wrapNumbers: true}).IntValue;
+          assert.deepStrictEqual(actual, expected);
           done();
         });
       });
@@ -355,9 +348,7 @@ describe('Spanner', () => {
 
         insert({IntArray: values}, (err, row) => {
           assert.ifError(err);
-
-          const expected = values.map(Spanner.int);
-          assert.deepStrictEqual(row.toJSON().IntArray, expected);
+          assert.deepStrictEqual(row.toJSON().IntArray, values);
           done();
         });
       });
@@ -365,7 +356,7 @@ describe('Spanner', () => {
 
     describe('float64s', () => {
       it('should write float64 values', done => {
-        insert({FloatValue: Spanner.float(8.2)}, (err, row) => {
+        insert({FloatValue: 8.2}, (err, row) => {
           assert.ifError(err);
           assert.deepStrictEqual(row.toJSON().FloatValue, 8.2);
           done();
@@ -433,9 +424,7 @@ describe('Spanner', () => {
 
         insert({FloatArray: values}, (err, row) => {
           assert.ifError(err);
-
-          const expected = values.map(Spanner.float);
-          assert.deepStrictEqual(row.toJSON().FloatArray, expected);
+          assert.deepStrictEqual(row.toJSON().FloatArray, values);
           done();
         });
       });
@@ -1352,10 +1341,7 @@ describe('Spanner', () => {
       EXPECTED_ROW.DOB = DATE;
       EXPECTED_ROW.Float = FLOAT;
       EXPECTED_ROW.Int = INT;
-      EXPECTED_ROW.PhoneNumbers = [
-        Spanner.int(PHONE_NUMBERS[0]),
-        Spanner.int(PHONE_NUMBERS[1]),
-      ];
+      EXPECTED_ROW.PhoneNumbers = PHONE_NUMBERS;
 
       before(() => {
         return table.insert(INSERT_ROW);
diff --git a/test/batch-transaction.ts b/test/batch-transaction.ts
index 086c51c0b..38fe9bf78 100644
--- a/test/batch-transaction.ts
+++ b/test/batch-transaction.ts
@@ -123,26 +123,6 @@ describe('BatchTransaction', () => {
 
       batchTransaction.createQueryPartitions(QUERY.sql, done);
     });
-
-    it('should remove gax options from the query', done => {
-      const fakeQuery = {
-        sql: QUERY.sql,
-        gaxOptions: GAX_OPTS,
-      };
-
-      fakeCodec.encodeQuery = (query) => {
-        assert.strictEqual(query, fakeQuery);
-        return extend({a: 'b'}, QUERY);
-      };
-
-      batchTransaction.createPartitions_ = (config, callback) => {
-        assert.deepStrictEqual(config.reqOpts, {sql: QUERY.sql, a: 'b'});
-        assert.strictEqual(config.gaxOpts, GAX_OPTS);
-        callback();  // the done fn
-      };
-
-      batchTransaction.createQueryPartitions(fakeQuery, done);
-    });
   });
 
   describe('createPartitions_', () => {
@@ -253,22 +233,6 @@ describe('BatchTransaction', () => {
 
       batchTransaction.createReadPartitions(query, done);
     });
-
-    it('should remove gax options from the query', done => {
-      const query = {gaxOptions: GAX_OPTS};
-
-      fakeCodec.encodeRead = () => {
-        return extend({}, QUERY);
-      };
-
-      batchTransaction.createPartitions_ = (config, callback) => {
-        assert.deepStrictEqual(config.reqOpts, {table: QUERY.table});
-        assert.strictEqual(config.gaxOpts, GAX_OPTS);
-        callback();  // the done fn
-      };
-
-      batchTransaction.createReadPartitions(query, done);
-    });
   });
 
   describe('execute', () => {
diff --git a/test/codec.ts b/test/codec.ts
index 5a275c7bb..226e57adc 100644
--- a/test/codec.ts
+++ b/test/codec.ts
@@ -17,47 +17,30 @@
 'use strict';
 
 import * as assert from 'assert';
-import * as extend from 'extend';
 import * as proxyquire from 'proxyquire';
-import {util} from '@google-cloud/common-grpc';
+import * as sinon from 'sinon';
+import {Service} from '@google-cloud/common-grpc';
 
-class FakeGrpcService {
-  static encodeValue_ = util.noop;
-  static decodeValue_ = util.noop;
-}
+import {SpannerClient as s} from '../src/v1';
 
 describe('codec', () => {
-  let codecCached;
   let codec;
 
-  const TYPES = [
-    'unspecified',
-    'bool',
-    'int64',
-    'float64',
-    'timestamp',
-    'date',
-    'string',
-    'bytes',
-    'array',
-    'struct',
-  ];
+  const sandbox = sinon.createSandbox();
 
   before(() => {
     codec = proxyquire('../src/codec.js', {
-              '@google-cloud/common-grpc': {
-                Service: FakeGrpcService,
-              },
+              '@google-cloud/common-grpc': {Service},
             }).codec;
-    codecCached = extend({}, codec);
   });
 
   beforeEach(() => {
-    extend(codec, codecCached);
-    FakeGrpcService.encodeValue_ = util.noop;
-    FakeGrpcService.decodeValue_ = util.noop;
+    sandbox.stub(Service, 'encodeValue_').callsFake(value => value);
+    sandbox.stub(Service, 'decodeValue_').callsFake(value => value);
   });
 
+  afterEach(() => sandbox.restore());
+
   describe('SpannerDate', () => {
     it('should choke on multiple arguments', () => {
       const expectedErrorMessage = [
@@ -126,96 +109,49 @@ describe('codec', () => {
   });
 
   describe('Struct', () => {
-    let generateToJSONFromRow_;
-
-    before(() => {
-      generateToJSONFromRow_ = codec.generateToJSONFromRow;
-    });
-
-    afterEach(() => {
-      codec.generateToJSONFromRow = generateToJSONFromRow_;
-    });
-
-    describe('initialization', () => {
-      it('should create an array', () => {
+    describe('toJSON', () => {
+      it('should covert the struct to JSON', () => {
         const struct = new codec.Struct();
-        assert(Array.isArray(struct));
-      });
+        const options = {};
+        const fakeJson = {};
 
-      it('should set the type', () => {
-        const struct = new codec.Struct();
-        const type = struct[codec.TYPE];
+        const stub = sandbox.stub(codec, 'convertFieldsToJson')
+                         .withArgs(struct, options)
+                         .returns(fakeJson);
 
-        assert.strictEqual(codec.Struct.TYPE, 'struct');
-        assert.strictEqual(type, codec.Struct.TYPE);
+        assert.strictEqual(struct.toJSON(options), fakeJson);
       });
+    });
 
-      it('should create a toJSON property', () => {
-        const fakeJSON = {};
-        let cachedStruct;
-
-        codec.generateToJSONFromRow = (struct) => {
-          cachedStruct = struct;
-          return fakeJSON;
-        };
+    describe('fromArray', () => {
+      it('should wrap the array in a struct', () => {
+        const fields = [{name: 'name', value: 'value'}];
+        const struct = codec.Struct.fromArray(fields);
 
-        const struct = new codec.Struct();
+        assert(struct instanceof codec.Struct);
 
-        assert.strictEqual(struct, cachedStruct);
-        assert.strictEqual(struct.toJSON, fakeJSON);
+        fields.forEach((field, i) => {
+          assert.strictEqual(struct[i], field);
+        });
       });
     });
 
     describe('fromJSON', () => {
-      it('should capture the key value pairs', () => {
+      it('should covert json to a struct', () => {
         const json = {a: 'b', c: 'd'};
+        const expected = [{name: 'a', value: 'b'}, {name: 'c', value: 'd'}];
         const struct = codec.Struct.fromJSON(json);
 
-        const expected = new codec.Struct();
-        expected.push.apply(expected, [
-          {name: 'a', value: 'b'},
-          {name: 'c', value: 'd'},
-        ]);
-        assert.deepStrictEqual(struct, expected);
-      });
-    });
+        assert(struct instanceof codec.Struct);
 
-    describe('fromArray', () => {
-      it('should convert array to struct array', () => {
-        const arr = [{name: 'a', value: 1}, {name: 'b', value: 2}];
-        const struct = codec.Struct.fromArray(arr);
-
-        const expectedStruct = new codec.Struct();
-        expectedStruct.push.apply(expectedStruct, arr);
-
-        assert(codec.Struct.isStruct(struct));
-        assert.deepStrictEqual(struct, expectedStruct);
-      });
-    });
-
-    describe('isStruct', () => {
-      it('should return true for structs', () => {
-        const struct = new codec.Struct();
-        const isStruct = codec.Struct.isStruct(struct);
-
-        assert.strictEqual(isStruct, true);
-      });
-
-      it('should return false for arrays', () => {
-        const isStruct = codec.Struct.isStruct([]);
-
-        assert.strictEqual(isStruct, false);
-      });
-
-      it('should return false for falsey values', () => {
-        const isStruct = codec.Struct.isStruct(null);
-
-        assert.strictEqual(isStruct, false);
+        expected.forEach((field, i) => {
+          assert.deepStrictEqual(struct[i], field);
+        });
       });
     });
   });
 
-  describe('generateToJSONFromRow', () => {
+  describe('convertFieldsToJson', () => {
     const ROW = [
       {
         name: 'name',
@@ -223,26 +159,14 @@ describe('codec', () => {
       },
     ];
 
-    let toJSON;
-
-    beforeEach(() => {
-      toJSON = codec.generateToJSONFromRow(ROW);
-    });
-
-    it('should return a function', () => {
-      assert.strictEqual(typeof toJSON, 'function');
-    });
-
     it('should not require options', () => {
-      assert.doesNotThrow(() => {
-        toJSON();
-      });
+      assert.doesNotThrow(() => codec.convertFieldsToJson(ROW));
     });
 
     it('should return serialized rows', () => {
-      assert.deepStrictEqual(toJSON(), {
-        name: 'value',
-      });
+      const json = codec.convertFieldsToJson(ROW);
+
+      assert.deepStrictEqual(json, {name: 'value'});
     });
 
     it('should not return nameless values', () => {
@@ -252,73 +176,142 @@ describe('codec', () => {
         },
       ];
 
-      const toJSON = codec.generateToJSONFromRow(row);
-      assert.deepStrictEqual(toJSON(), {});
+      const json = codec.convertFieldsToJson(row);
+      assert.deepStrictEqual(json, {});
     });
 
-    it('should not wrap numbers by default', () => {
-      const row = [
-        {
-          name: 'Number',
-          value: new codec.Int(3),
-        },
-      ];
+    describe('structs', () => {
+      it('should not wrap structs by default', () => {
+        const options = {wrapNumbers: false, wrapStructs: false};
+        const fakeStructJson = {};
+
+        const struct = new codec.Struct();
+        const stub = sandbox.stub(struct, 'toJSON').returns(fakeStructJson);
+
+        const row = [
+          {name: 'Struct', value: struct},
+        ];
+
+        const json = codec.convertFieldsToJson(row, options);
+
+        assert.strictEqual(json.Struct, fakeStructJson);
+        assert.deepStrictEqual(stub.lastCall.args[0], options);
+      });
+
+      it('should wrap structs with option', () => {
+        const value = 3.3;
 
-      const toJSON = codec.generateToJSONFromRow(row);
-      assert.strictEqual(typeof toJSON().Number, 'number');
-      assert.strictEqual(toJSON().Number, 3);
+        const expectedStruct = codec.Struct.fromJSON({Number: value});
+        const struct = codec.Struct.fromJSON({Number: new codec.Float(value)});
+
+        const row = [
+          {name: 'Struct', value: struct},
+        ];
+
+        const json = codec.convertFieldsToJson(row, {wrapStructs: true});
+        assert.deepStrictEqual(json.Struct, expectedStruct);
+      });
     });
 
-    it('should wrap numbers with option', () => {
-      const int = new codec.Int(3);
+    describe('numbers', () => {
+      it('should not wrap numbers by default', () => {
+        const row = [
+          {
+            name: 'Number',
+            value: new codec.Int(3),
+          },
+        ];
 
-      const row = [
-        {
-          name: 'Number',
-          value: int,
-        },
-      ];
+        const json = codec.convertFieldsToJson(row);
+        assert.strictEqual(typeof json.Number, 'number');
+        assert.strictEqual(json.Number, 3);
+      });
+
+      it('should wrap numbers with option', () => {
+        const int = new codec.Int(3);
+
+        const row = [
+          {
+            name: 'Number',
+            value: int,
+          },
+        ];
+
+        const json = codec.convertFieldsToJson(row, {wrapNumbers: true});
 
-      const toJSON = codec.generateToJSONFromRow(row);
-      const value = toJSON({wrapNumbers: true}).Number;
+        assert(json.Number instanceof codec.Int);
+        assert.deepStrictEqual(json.Number, int);
+      });
 
-      assert(value instanceof codec.Int);
-      assert.deepStrictEqual(value, int);
+      it('should throw an error if number is out of bounds', () => {
+        const int = new codec.Int('9223372036854775807');
+
+        const row = [
+          {
+            name: 'Number',
+            value: int,
+          },
+        ];
+
+        assert.throws(() => {
+          codec.convertFieldsToJson(row);
+        }, new RegExp('Serializing column "Number" encountered an error'));
+      });
     });
 
-    it('should throw an error if number is out of bounds', () => {
-      const int = new codec.Int('9223372036854775807');
+    describe('arrays', () => {
+      it('should not wrap numbers by default', () => {
+        const value = 3;
 
-      const row = [
-        {
-          name: 'Number',
-          value: int,
-        },
-      ];
+        const row = [
+          {
+            name: 'List',
+            value: [new codec.Int(value)],
+          },
+        ];
 
-      const toJSON = codec.generateToJSONFromRow(row);
+        const json = codec.convertFieldsToJson(row);
+        assert.deepStrictEqual(json.List, [value]);
+      });
 
-      assert.throws(() => {
-        toJSON();
-      }, new RegExp('Serializing column "Number" encountered an error'));
+      it('should wrap numbers with option', () => {
+        const value = new codec.Int(3);
+
+        const row = [{name: 'List', value: [value]}];
+
+        const json = codec.convertFieldsToJson(row, {wrapNumbers: true});
+        assert.deepStrictEqual(json.List, [value]);
+      });
+
+      it('should not wrap structs by default', () => {
+        const struct = new codec.Struct();
+        const expectedStruct = {a: 'b', c: 'd'};
+
+        sandbox.stub(struct, 'toJSON').returns(expectedStruct);
+
+        const row = [{name: 'List', value: [struct]}];
+
+        const json = codec.convertFieldsToJson(row);
+        assert.deepStrictEqual(json.List, [expectedStruct]);
+      });
+
+      it('should wrap structs with option', () => {
+        const expectedStruct = codec.Struct.fromJSON({a: 'b', c: 'd'});
+
+        const row = [{name: 'List', value: [expectedStruct]}];
+
+        const json = codec.convertFieldsToJson(row, {wrapStructs: true});
+        assert.deepStrictEqual(json.List, [expectedStruct]);
+      });
     });
   });
 
   describe('decode', () => {
     // Does not require any special decoding.
     const BYPASS_FIELD = {
-      type: {
-        code: 'not-real-code',
-      },
+      code: 'not-real-code',
     };
 
-    beforeEach(() => {
-      // tslint:disable-next-line no-any
-      (FakeGrpcService as any).decodeValue_ = (value) => {
-        return value;
-      };
-    });
-
     it('should return the same value if not a special type', () => {
       const value = {};
 
@@ -327,31 +320,27 @@ describe('codec', () => {
     });
 
     it('should return null values as null', () => {
-      FakeGrpcService.decodeValue_ = () => null;
+      (Service.decodeValue_ as sinon.SinonStub).returns(null);
       const decoded = codec.decode(null, BYPASS_FIELD);
       assert.strictEqual(decoded, null);
     });
 
     it('should decode BYTES', () => {
-      const value = Buffer.from('bytes value');
+      const expected = Buffer.from('bytes value');
+      const encoded = expected.toString('base64');
 
-      const decoded = codec.decode(value.toString('base64'), {
-        type: {
-          code: 'BYTES',
-        },
+      const decoded = codec.decode(encoded, {
+        code: s.TypeCode.BYTES,
       });
 
-      // tslint:disable-next-line: no-any
-      assert.deepStrictEqual(decoded, Buffer.from(value as any, 'base64'));
+      assert.deepStrictEqual(decoded, expected);
     });
 
     it('should decode FLOAT64', () => {
       const value = 'Infinity';
 
       const decoded = codec.decode(value, {
-        type: {
-          code: 'FLOAT64',
-        },
+        code: s.TypeCode.FLOAT64,
       });
 
       assert(decoded instanceof codec.Float);
@@ -362,9 +351,7 @@ describe('codec', () => {
       const value = '64';
 
       const decoded = codec.decode(value, {
-        type: {
-          code: 'INT64',
-        },
+        code: s.TypeCode.INT64,
       });
 
       assert(decoded instanceof codec.Int);
@@ -375,9 +362,7 @@ describe('codec', () => {
       const value = new Date();
 
       const decoded = codec.decode(value.toJSON(), {
-        type: {
-          code: 'TIMESTAMP',
-        },
+        code: s.TypeCode.TIMESTAMP,
       });
 
       assert.deepStrictEqual(decoded, value);
@@ -387,9 +372,7 @@ describe('codec', () => {
       const value = new Date();
 
       const decoded = codec.decode(value.toJSON(), {
-        type: {
-          code: 'DATE',
-        },
+        code: s.TypeCode.DATE,
       });
 
       assert.deepStrictEqual(decoded, value);
@@ -399,11 +382,9 @@ describe('codec', () => {
       const value = ['1'];
 
       const decoded = codec.decode(value, {
-        type: {
-          code: 'ARRAY',
-          arrayElementType: {
-            code: 'INT64',
-          },
+        code: s.TypeCode.ARRAY,
+        arrayElementType: {
+          code: s.TypeCode.INT64,
         },
       });
 
@@ -415,58 +396,38 @@ describe('codec', () => {
         fieldName: '1',
       };
 
-      const int = {int: true};
-      codec.Int = class {
-        constructor(value_) {
-          assert.strictEqual(value_, value.fieldName);
-          return int;
-        }
-      };
-
       const decoded = codec.decode(value, {
-        type: {
-          code: 'STRUCT',
-          structType: {
-            fields: [
-              {
-                name: 'fieldName',
-                type: {
-                  code: 'INT64',
-                },
+        code: s.TypeCode.STRUCT,
+        structType: {
+          fields: [
+            {
+              name: 'fieldName',
+              type: {
+                code: s.TypeCode.INT64,
               },
-            ],
-          },
+            },
+          ],
         },
       });
-      assert(codec.Struct.isStruct(decoded));
 
-      const expectedStruct = new codec.Struct();
-      expectedStruct.push.apply(expectedStruct, [
-        {
-          name: 'fieldName',
-          value: int,
-        },
-      ]);
+      const expectedStruct = new codec.Struct({
+        name: 'fieldName',
+        value: new codec.Int(value.fieldName),
+      });
 
+      assert(decoded instanceof codec.Struct);
       assert.deepStrictEqual(decoded, expectedStruct);
     });
   });
 
   describe('encode', () => {
-    beforeEach(() => {
-      // tslint:disable-next-line no-any
-      (FakeGrpcService as any).encodeValue_ = value => value;
-    });
-
     it('should return the value from the common encoder', () => {
       const value = {};
       const defaultEncodedValue = {};
 
-      // tslint:disable-next-line no-any
-      (FakeGrpcService as any).encodeValue_ = (value_) => {
-        assert.strictEqual(value_, value);
-        return defaultEncodedValue;
-      };
+      (Service.encodeValue_ as sinon.SinonStub)
+          .withArgs(value)
+          .returns(defaultEncodedValue);
 
       const encoded = codec.encode(value);
       assert.strictEqual(encoded, defaultEncodedValue);
@@ -483,7 +444,7 @@ describe('codec', () => {
     it('should encode structs', () => {
       const value = codec.Struct.fromJSON({a: 'b', c: 'd'});
       const encoded = codec.encode(value);
-      assert.deepStrictEqual([].concat(encoded.slice()), ['b', 'd']);
+      assert.deepStrictEqual(encoded, ['b', 'd']);
     });
 
     it('should stringify Infinity', () => {
@@ -557,154 +518,105 @@ describe('codec', () => {
 
       assert.strictEqual(encoded, 10);
     });
-
-    it('should encode each key in a dictionary-like object', () => {
-      const obj = {
-        f: new codec.Float(10),
-        i: new codec.Int(10),
-      };
-      const encoded = codec.encode(obj);
-      assert.deepStrictEqual(encoded, {f: 10, i: '10'});
-    });
-
-    it('should only encode public properties of objects', () => {
-      const obj = {
-        hasOwnProperty(key) {
-          // jshint ignore:line
-          return key === 'public';
-        },
-        _private: new codec.Int(10),
-        public: new codec.Int(10),
-      };
-      const encoded = codec.encode(obj);
-      assert.deepStrictEqual(encoded._private, obj._private);
-      assert.deepStrictEqual(encoded.public, '10');
-    });
   });
 
   describe('getType', () => {
     it('should determine if the value is a boolean', () => {
-      assert.strictEqual(codec.getType(true), 'bool');
+      assert.deepStrictEqual(codec.getType(true), {type: 'bool'});
     });
 
     it('should determine if the value is a float', () => {
-      assert.strictEqual(codec.getType(NaN), 'float64');
-      assert.strictEqual(codec.getType(Infinity), 'float64');
-      assert.strictEqual(codec.getType(-Infinity), 'float64');
-      assert.strictEqual(codec.getType(2.2), 'float64');
-      assert.strictEqual(codec.getType(new codec.Float(1.1)), 'float64');
+      assert.deepStrictEqual(codec.getType(NaN), {type: 'float64'});
+      assert.deepStrictEqual(codec.getType(Infinity), {type: 'float64'});
+      assert.deepStrictEqual(codec.getType(-Infinity), {type: 'float64'});
+      assert.deepStrictEqual(codec.getType(2.2), {type: 'float64'});
+      assert.deepStrictEqual(
+          codec.getType(new codec.Float(1.1)), {type: 'float64'});
     });
 
     it('should determine if the value is an int', () => {
-      assert.strictEqual(codec.getType(1234), 'int64');
-      assert.strictEqual(codec.getType(new codec.Int(1)), 'int64');
+      assert.deepStrictEqual(codec.getType(1234), {type: 'int64'});
+      assert.deepStrictEqual(codec.getType(new codec.Int(1)), {type: 'int64'});
     });
 
     it('should determine if the value is a string', () => {
-      assert.strictEqual(codec.getType('abc'), 'string');
+      assert.deepStrictEqual(codec.getType('abc'), {type: 'string'});
     });
 
     it('should determine if the value is bytes', () => {
-      assert.strictEqual(codec.getType(Buffer.from('abc')), 'bytes');
+      assert.deepStrictEqual(
+          codec.getType(Buffer.from('abc')), {type: 'bytes'});
     });
 
     it('should determine if the value is a timestamp', () => {
-      assert.strictEqual(codec.getType(new Date()), 'timestamp');
+      assert.deepStrictEqual(codec.getType(new Date()), {type: 'timestamp'});
     });
 
     it('should determine if the value is a date', () => {
-      assert.strictEqual(codec.getType(new codec.SpannerDate()), 'date');
+      assert.deepStrictEqual(
+          codec.getType(new codec.SpannerDate()), {type: 'date'});
     });
 
     it('should determine if the value is a struct', () => {
       const struct = codec.Struct.fromJSON({a: 'b'});
       const type = codec.getType(struct);
-      assert.strictEqual(type.type, 'struct');
-      assert.deepStrictEqual([].concat(type.fields.slice()), [
-        {
-          name: 'a',
-          type: 'string',
-        },
-      ]);
+
+      assert.deepStrictEqual(type, {
+        type: 'struct',
+        fields: [
+          {name: 'a', type: 'string'},
+        ]
+      });
     });
 
     it('should attempt to determine arrays and their values', () => {
       assert.deepStrictEqual(codec.getType([Infinity]), {
         type: 'array',
-        child: 'float64',
+        child: {
+          type: 'float64',
+        }
       });
     });
 
     it('should return unspecified for unknown values', () => {
-      assert.strictEqual(codec.getType(null), 'unspecified');
+      assert.deepStrictEqual(codec.getType(null), {type: 'unspecified'});
 
       assert.deepStrictEqual(codec.getType([null]), {
         type: 'array',
-        child: 'unspecified',
+        child: {
+          type: 'unspecified',
+        }
       });
     });
   });
 
-  describe('TYPES', () => {
-    it('should export types', () => {
-      assert.deepStrictEqual(codec.TYPES, TYPES);
-    });
-  });
-
   describe('encodeQuery', () => {
-    let createTypeObject_;
-
+    const SQL = 'SELECT * FROM table';
     const QUERY = {
-      sql: 'SELECT * FROM table',
-      a: 'b',
-      c: 'd',
+      sql: SQL,
     };
 
-    before(() => {
-      createTypeObject_ = codec.createTypeObject;
-    });
-
-    afterEach(() => {
-      codec.createTypeObject = createTypeObject_;
-    });
-
     it('should return the query', () => {
-      const fakeQuery = {
-        a: 'b',
-        c: 'd',
-      };
-
-      const encodedQuery = codec.encodeQuery(fakeQuery);
+      const encodedQuery = codec.encodeQuery(QUERY);
 
-      assert.deepStrictEqual(fakeQuery, encodedQuery);
+      assert.deepStrictEqual(QUERY, encodedQuery);
     });
 
     it('should clone the query', () => {
-      const fakeQuery = {
-        a: 'b',
-      };
-
-      const encodedQuery = codec.encodeQuery(fakeQuery);
-      assert.notStrictEqual(fakeQuery, encodedQuery);
+      const encodedQuery = codec.encodeQuery(QUERY);
+      assert.notStrictEqual(QUERY, encodedQuery);
 
-      delete encodedQuery.a;
-      assert.strictEqual(fakeQuery.a, 'b');
+      delete encodedQuery.sql;
+      assert.strictEqual(QUERY.sql, SQL);
     });
 
     it('should encode query parameters', () => {
-      const fakeQuery = {
-        sql: QUERY,
-        params: {
-          test: 'value',
-        },
-      };
-
       const encodedValue = {};
+      const fakeQuery = Object.assign({}, QUERY, {params: {test: 'value'}});
 
-      codec.encode = (field) => {
-        assert.strictEqual(field, fakeQuery.params.test);
-        return encodedValue;
-      };
+      sandbox.stub(codec, 'encode')
+          .withArgs(fakeQuery.params.test)
+          .returns(encodedValue);
 
       const encodedQuery = codec.encodeQuery(fakeQuery);
       assert.strictEqual(encodedQuery.params.fields.test, encodedValue);
@@ -722,86 +634,53 @@ describe('codec', () => {
         bytes: Buffer.from('abc'),
       };
 
-      const types = Object.keys(params);
-
-      const fakeQuery = {
-        sql: QUERY,
-        params,
-      };
-
-      let getTypeCallCount = 0;
-
-      codec.getType = (field) => {
-        const type = types[getTypeCallCount++];
-
-        assert.strictEqual(params[type], field);
-        return type;
-      };
-
+      const fakeQuery = Object.assign({}, QUERY, {params});
       const encodedQuery = codec.encodeQuery(fakeQuery);
 
       assert.deepStrictEqual(encodedQuery.paramTypes, {
         unspecified: {
-          code: 0,
+          code: s.TypeCode.TYPE_CODE_UNSPECIFIED,
         },
         bool: {
-          code: 1,
+          code: s.TypeCode.BOOL,
         },
         int64: {
-          code: 2,
+          code: s.TypeCode.INT64,
         },
         float64: {
-          code: 3,
+          code: s.TypeCode.FLOAT64,
         },
         timestamp: {
-          code: 4,
+          code: s.TypeCode.TIMESTAMP,
         },
         date: {
-          code: 5,
+          code: s.TypeCode.DATE,
         },
         string: {
-          code: 6,
+          code: s.TypeCode.STRING,
         },
         bytes: {
-          code: 7,
+          code: s.TypeCode.BYTES,
         },
       });
     });
 
     it('should not overwrite existing type definitions', () => {
-      const fakeQuery = {
+      const fakeQuery = Object.assign({}, QUERY, {
         params: {
           test: 123,
         },
         types: {
           test: 'string',
         },
-      };
-
-      codec.getType = () => {
-        throw new Error('Should not be called');
-      };
-
-      codec.encodeQuery(fakeQuery);
-    });
-
-    it('should create type objects', () => {
-      const fakeQuery = {
-        types: {
-          test: 'string',
-        },
-      };
-
-      const fakeTypeObject = {};
+      });
 
-      codec.createTypeObject = (type) => {
-        assert.strictEqual(type, 'string');
-        return fakeTypeObject;
-      };
+      sandbox.stub(codec, 'getType').throws();
 
       const query = codec.encodeQuery(fakeQuery);
 
-      assert.deepStrictEqual(query.paramTypes, {test: fakeTypeObject});
+      assert.deepStrictEqual(
+          query.paramTypes, {test: {code: s.TypeCode.STRING}});
     });
 
     it('should delete the type map from the request options', () => {
@@ -820,41 +699,34 @@ describe('codec', () => {
   });
 
   describe('encodeRead', () => {
+    it('should return all keys if ranges/keys are absent', () => {
+      const encoded = codec.encodeRead({});
+
+      assert.deepStrictEqual(encoded, {keySet: {all: true}});
+    });
+
     describe('query.keys', () => {
       it('should encode and map input to keySet', () => {
+        const keyMap = {key: {}, composite: {}, key2: {}};
+
         const query = {
-          keys: ['key', ['composite', 'key']],
+          keys: [
+            'key', ['composite', 'key2'],  // composite key
+          ],
         };
 
-        const encodedValue = {};
-        let numEncodeRequests = 0;
-
-        codec.encode = (key) => {
-          numEncodeRequests++;
-
-          switch (numEncodeRequests) {
-            case 1:
-              assert.strictEqual(key, query.keys[0]);
-              break;
-            case 2:
-              assert.strictEqual(key, query.keys[1][0]);
-              break;
-            case 3:
-              assert.strictEqual(key, query.keys[1][1]);
-              break;
-            default:
-              break;
-          }
+        const stub = sandbox.stub(codec, 'encode');
 
-          return encodedValue;
-        };
+        Object.keys(keyMap).forEach(key => {
+          stub.withArgs(key).returns(keyMap[key]);
+        });
 
         const expectedKeys = [
           {
-            values: [encodedValue],
+            values: [keyMap.key],
           },
           {
-            values: [encodedValue, encodedValue],
+            values: [keyMap.composite, keyMap.key2],
           },
         ];
 
@@ -862,47 +734,15 @@ describe('codec', () => {
         assert.deepStrictEqual(encoded.keySet.keys, expectedKeys);
       });
 
-      it('should accept just a key', () => {
-        const query = 'key';
-
-        const encodedValue = {};
-        codec.encode = (key) => {
-          assert.strictEqual(key, query);
-          return encodedValue;
-        };
-
-        const encoded = codec.encodeRead(query);
-
-        assert.strictEqual(encoded.keySet.keys[0].values[0], encodedValue);
-      });
-
-      it('should accept just an array of keys', () => {
-        const query = ['key'];
-
-        const encodedValue = {};
-        codec.encode = (key) => {
-          assert.strictEqual(key, query[0]);
-          return encodedValue;
-        };
-
-        const encoded = codec.encodeRead(query);
-
-        assert.strictEqual(encoded.keySet.keys[0].values[0], encodedValue);
-      });
-
       it('should arrify query.keys', () => {
-        const query = {
-          keys: 'key',
-        };
-
+        const query = {keys: 'key'};
         const encodedValue = {};
-        codec.encode = (key) => {
-          assert.strictEqual(key, query.keys);
-          return encodedValue;
-        };
 
-        const encoded = codec.encodeRead(query);
+        sandbox.stub(codec, 'encode')
+            .withArgs(query.keys)
+            .returns(encodedValue);
 
+        const encoded = codec.encodeRead(query);
         assert.strictEqual(encoded.keySet.keys[0].values[0], encodedValue);
       });
 
@@ -912,50 +752,47 @@ describe('codec', () => {
         };
 
         const encoded = codec.encodeRead(query);
-
         assert.strictEqual(encoded.keys, undefined);
       });
     });
 
     describe('query.ranges', () => {
       it('should encode/map the inputs', () => {
+        const keyMap = {key: {}, composite: {}, key2: {}};
+
         const query = {
           ranges: [
             {
               startOpen: 'key',
-              endClosed: ['composite', 'key'],
+              endClosed: ['composite', 'key2'],
             },
           ],
         };
 
-        const encodedValue = {};
-        let numEncodeRequests = 0;
-
-        codec.encode = (key) => {
-          const keys = ['key', 'composite', 'key'];
+        const stub = sandbox.stub(codec, 'encode');
 
-          assert.strictEqual(key, keys[numEncodeRequests++]);
-          return encodedValue;
-        };
+        Object.keys(keyMap).forEach(key => {
+          stub.withArgs(key).returns(keyMap[key]);
+        });
 
         const expectedRanges = [
           {
             startOpen: {
-              values: [encodedValue],
+              values: [keyMap.key],
             },
             endClosed: {
-              values: [encodedValue, encodedValue],
+              values: [keyMap.composite, keyMap.key2],
             },
           },
         ];
 
         const encoded = codec.encodeRead(query);
-
-        assert.strictEqual(numEncodeRequests, 3);
         assert.deepStrictEqual(encoded.keySet.ranges, expectedRanges);
       });
 
       it('should arrify query.ranges', () => {
+        const keyMap = {start: {}, end: {}};
+
         const query = {
           ranges: [
             {
@@ -965,28 +802,24 @@ describe('codec', () => {
           ],
         };
 
-        const encodedValue = {};
-        let numEncodeRequests = 0;
+        const stub = sandbox.stub(codec, 'encode');
 
-        codec.encode = (key) => {
-          assert.strictEqual(key, ['start', 'end'][numEncodeRequests++]);
-          return encodedValue;
-        };
+        Object.keys(keyMap).forEach(key => {
+          stub.withArgs(key).returns(keyMap[key]);
+        });
 
         const expectedRanges = [
           {
             startOpen: {
-              values: [encodedValue],
+              values: [keyMap.start],
             },
             endClosed: {
-              values: [encodedValue],
+              values: [keyMap.end],
             },
           },
         ];
 
         const encoded = codec.encodeRead(query);
-
-        assert.strictEqual(numEncodeRequests, 2);
         assert.deepStrictEqual(encoded.keySet.ranges, expectedRanges);
       });
 
@@ -1008,18 +841,56 @@ describe('codec', () => {
   });
 
   describe('createTypeObject', () => {
-    it('should convert the type to its int value', () => {
-      TYPES.forEach((typeName, i) => {
-        const type = codec.createTypeObject(typeName);
+    it('should convert strings to the corresponding type', () => {
+      const typeMap = {
+        unspecified: {
+          code: s.TypeCode.TYPE_CODE_UNSPECIFIED,
+        },
+        bool: {
+          code: s.TypeCode.BOOL,
+        },
+        int64: {
+          code: s.TypeCode.INT64,
+        },
+        float64: {
+          code: s.TypeCode.FLOAT64,
+        },
+        timestamp: {
+          code: s.TypeCode.TIMESTAMP,
+        },
+        date: {
+          code: s.TypeCode.DATE,
+        },
+        string: {
+          code: s.TypeCode.STRING,
+        },
+        bytes: {
+          code: s.TypeCode.BYTES,
+        },
+        array: {
+          code: s.TypeCode.ARRAY,
+          arrayElementType: {
+            code: s.TypeCode.TYPE_CODE_UNSPECIFIED,
+          }
+        },
+        struct: {
+          code: s.TypeCode.STRUCT,
+          structType: {fields: []},
+        }
+      };
 
-        assert.deepStrictEqual(type.code, i);
+      Object.keys(typeMap).forEach(key => {
+        const type = codec.createTypeObject(key);
+        assert.deepStrictEqual(type, typeMap[key]);
       });
     });
 
     it('should default to unspecified for unknown types', () => {
       const type = codec.createTypeObject('unicorn');
 
-      assert.deepStrictEqual(type, {code: TYPES.indexOf('unspecified')});
+      assert.deepStrictEqual(type, {
+        code: s.TypeCode.TYPE_CODE_UNSPECIFIED,
+      });
     });
 
     it('should set the arrayElementType', () => {
@@ -1029,9 +900,9 @@ describe('codec', () => {
       });
 
       assert.deepStrictEqual(type, {
-        code: TYPES.indexOf('array'),
+        code: s.TypeCode.ARRAY,
         arrayElementType: {
-          code: TYPES.indexOf('bool'),
+          code: s.TypeCode.BOOL,
         },
       });
     });
@@ -1046,19 +917,19 @@ describe('codec', () => {
       });
 
       assert.deepStrictEqual(type, {
-        code: TYPES.indexOf('struct'),
+        code: s.TypeCode.STRUCT,
         structType: {
           fields: [
             {
               name: 'boolKey',
               type: {
-                code: TYPES.indexOf('bool'),
+                code: s.TypeCode.BOOL,
               },
             },
             {
               name: 'intKey',
               type: {
-                code: TYPES.indexOf('int64'),
+                code: s.TypeCode.INT64,
               },
             },
           ],
@@ -1072,32 +943,32 @@ describe('codec', () => {
         fields: [
           {
             name: 'nestedStruct',
-            type: {
-              type: 'struct',
-              fields: [
-                {
-                  type: 'bool',
-                  name: 'boolKey',
-                },
-              ],
-            },
+            type: 'struct',
+            fields: [
+              {
+                type: 'bool',
+                name: 'boolKey',
+              },
+            ],
           },
         ],
       });
 
       assert.deepStrictEqual(type, {
-        code: TYPES.indexOf('struct'),
+        code: s.TypeCode.STRUCT,
         structType: {
           fields: [
             {
               name: 'nestedStruct',
               type: {
-                code: TYPES.indexOf('struct'),
+                code: s.TypeCode.STRUCT,
                 structType: {
                   fields: [
                     {
                       name: 'boolKey',
-                      type: {code: TYPES.indexOf('bool')},
+                      type: {
+                        code: s.TypeCode.BOOL,
+                      },
                     },
                   ],
                 },
diff --git a/test/row-builder.ts b/test/row-builder.ts
index 6b3952871..e6d748d7c 100644
--- a/test/row-builder.ts
+++ b/test/row-builder.ts
@@ -18,21 +18,11 @@ import {util} from '@google-cloud/common-grpc';
 import * as assert from 'assert';
 import * as extend from 'extend';
 import * as proxyquire from 'proxyquire';
+import * as sinon from 'sinon';
 
 import {codec} from '../src/codec';
 import * as rb from '../src/row-builder';
-
-let decodeOverride;
-let generateToJSONFromRowOverride;
-const fakeCodec = {
-  decode() {
-    return (decodeOverride || codec.decode).apply(null, arguments);
-  },
-  generateToJSONFromRow() {
-    return (generateToJSONFromRowOverride || codec.generateToJSONFromRow)
-        .apply(null, arguments);
-  },
-};
+import {SpannerClient as s} from '../src/v1';
 
 class FakeGrpcService {
   static decodeValue_(value) {}
@@ -45,6 +35,7 @@ describe('RowBuilder', () => {
   let RowBuilderCached: typeof rb.RowBuilder;
   let rowBuilder: rb.RowBuilder;
 
+  const sandbox = sinon.createSandbox();
   const FIELDS = [{}, {}];
 
   before(() => {
@@ -52,19 +43,19 @@ describe('RowBuilder', () => {
                    '@google-cloud/common-grpc': {
                      Service: FakeGrpcService,
                    },
-                   './codec.js': {codec: fakeCodec},
+                   './codec.js': {codec},
                  }).RowBuilder;
     RowBuilderCached = extend({}, RowBuilder);
   });
 
   beforeEach(() => {
     FakeGrpcService.decodeValue_ = util.noop;
-    decodeOverride = null;
-    generateToJSONFromRowOverride = null;
     extend(RowBuilder, RowBuilderCached);
     rowBuilder = new RowBuilder(FIELDS);
   });
 
+  afterEach(() => sandbox.restore());
+
   describe('acceptance tests', () => {
     const TESTS =
         require('../../test/data/streaming-read-acceptance-test.json').tests;
@@ -169,85 +160,6 @@ describe('RowBuilder', () => {
     });
   });
 
-  describe('formatValue', () => {
-    it('should iterate an array', () => {
-      const field = {
-        code: 'ARRAY',
-        arrayElementType: 'type',
-      };
-
-      const value = [{}];
-      const decodedValue = {};
-
-      decodeOverride = (value_, field_) => {
-        assert.strictEqual(value_, value[0]);
-        assert.strictEqual(field_, field.arrayElementType);
-        return decodedValue;
-      };
-
-      const formattedValue = RowBuilder.formatValue(field, value);
-      assert.deepStrictEqual(formattedValue, [decodedValue]);
-    });
-
-    it('should return null if value is NULL_VALUE', () => {
-      const field = {
-        code: 'ARRAY',
-        arrayElementType: 'type',
-      };
-
-      const value = 'NULL_VALUE';
-
-      const formattedValue = RowBuilder.formatValue(field, value);
-      assert.strictEqual(formattedValue, null);
-    });
-
-    it('should return decoded value if not an array or struct', () => {
-      const field = {
-        code: 'NOT_STRUCT_OR_ARRAY',
-      };
-
-      const value = [{}];
-      const decodedValue = {};
-
-      decodeOverride = (value_, field_) => {
-        assert.strictEqual(value_, value);
-        assert.strictEqual(field_, field);
-        return decodedValue;
-      };
-
-      const formattedValue = RowBuilder.formatValue(field, value);
-      assert.strictEqual(formattedValue, decodedValue);
-    });
-
-    it('should iterate a struct', () => {
-      const field = {
-        code: 'STRUCT',
-        structType: {
-          fields: [
-            {
-              name: 'fieldName',
-              type: 'NOT_STRUCT_OR_ARRAY',  // so it returns original value
-            },
-          ],
-        },
-      };
-
-      const value = [{}];
-      const decodedValue = {};
-
-      decodeOverride = (value_, field_) => {
-        assert.strictEqual(value_, value[0]);
-        assert.strictEqual(field_, field.structType.fields[0]);
-        return decodedValue;
-      };
-
-      const formattedValue = RowBuilder.formatValue(field, value);
-      assert.deepStrictEqual(formattedValue, {
-        fieldName: decodedValue,
-      });
-    });
-  });
-
   describe('merge', () => {
     it('should merge arrays', () => {
       const type = {
@@ -523,15 +435,14 @@ describe('RowBuilder', () => {
     });
 
     it('should format the values', () => {
+      const value = ROWS[0][0];
+      const type = rowBuilder.fields[0].type;
+
       const formattedValue = {
         formatted: true,
       };
 
-      RowBuilder.formatValue = (field, value) => {
-        assert.strictEqual(field, rowBuilder.fields[0]);
-        assert.strictEqual(value, ROWS[0][0]);
-        return formattedValue;
-      };
+      sinon.stub(codec, 'decode').withArgs(value, type).returns(formattedValue);
 
       const rows = rowBuilder.toJSON(ROWS);
       const row = rows[0];
@@ -548,28 +459,23 @@ describe('RowBuilder', () => {
       });
     });
 
-    describe('toJSON', () => {
-      const toJSONOverride = () => {};
+    describe('Row#toJSON', () => {
       let FORMATTED_ROW;
 
       beforeEach(() => {
-        generateToJSONFromRowOverride = () => {
-          return toJSONOverride;
-        };
-
-        const formattedValue = {};
-
-        RowBuilder.formatValue = () => {
-          return formattedValue;
-        };
-
-        rowBuilder.rows = [[{}]];
-
         FORMATTED_ROW = rowBuilder.toJSON(ROWS)[0];
       });
 
       it('should assign a toJSON method', () => {
-        assert.strictEqual(FORMATTED_ROW.toJSON, toJSONOverride);
+        const fakeJson = {};
+        const fakeOptions = {wrapNumbers: false};
+
+        sandbox.stub(codec, 'convertFieldsToJson')
+            .withArgs(FORMATTED_ROW, fakeOptions)
+            .returns(fakeJson);
+
+        const json = FORMATTED_ROW.toJSON(fakeOptions);
+        assert.strictEqual(json, fakeJson);
       });
 
       it('should not include toJSON when iterated', () => {
diff --git a/test/transaction-request.ts b/test/transaction-request.ts
index 66d13dffa..84914824f 100644
--- a/test/transaction-request.ts
+++ b/test/transaction-request.ts
@@ -19,6 +19,7 @@ import * as pfy from '@google-cloud/promisify';
 import * as assert from 'assert';
 import * as extend from 'extend';
 import * as proxyquire from 'proxyquire';
+import * as sinon from 'sinon';
 import {split} from 'split-array-stream';
 import * as through from 'through2';
 
@@ -48,23 +49,20 @@ const fakePfy = extend({}, pfy, {
   },
 });
 
-const fakeCodec: typeof codec = {
-  encode: util.noop
-  // tslint:disable-next-line no-any
-} as any;
-
 describe('TransactionRequest', () => {
   // tslint:disable-next-line variable-name
   let TransactionRequest: typeof tr.TransactionRequest;
   let transactionRequest: tr.TransactionRequest;
 
+  const sandbox = sinon.createSandbox();
+
   before(() => {
     TransactionRequest = proxyquire('../src/transaction-request', {
                            '@google-cloud/common-grpc': {
                              Service: FakeGrpcService,
                            },
                            '@google-cloud/promisify': fakePfy,
-                           './codec.js': {codec: fakeCodec},
+                           './codec.js': {codec},
                            './partial-result-stream':
                                {partialResultStream: fakePartialResultStream},
                          }).TransactionRequest;
@@ -72,12 +70,13 @@ describe('TransactionRequest', () => {
 
   beforeEach(() => {
     FakeGrpcService.encodeValue_ = util.noop;
-    fakeCodec.encode = util.noop;
     transactionRequest = new TransactionRequest();
     transactionRequest.request = util.noop;
     transactionRequest.requestStream = util.noop;
   });
 
+  afterEach(() => sandbox.restore());
+
   describe('instantiation', () => {
     let formatTimestamp;
 
@@ -214,12 +213,12 @@ describe('TransactionRequest', () => {
 
   describe('createReadStream', () => {
     const TABLE = 'table-name';
-    const QUERY = {e: 'f'};
+    const QUERY = {session: 'a', table: 'b', keySet: {all: true}};
+
+    let stub: sinon.SinonStub;
 
     beforeEach(() => {
-      fakeCodec.encodeRead = () => {
-        return QUERY;
-      };
+      stub = sandbox.stub(codec, 'encodeRead').returns(QUERY);
     });
 
     it('should accept a query object', done => {
@@ -232,12 +231,9 @@ describe('TransactionRequest', () => {
         table: TABLE,
       });
 
-      fakeCodec.encodeRead = (readRequest) => {
-        assert.strictEqual(readRequest, query);
-        return QUERY;
-      };
-
       transactionRequest.requestStream = (options) => {
+        const [readRequest] = stub.lastCall.args;
+        assert.strictEqual(readRequest, query);
         assert.deepStrictEqual(options.reqOpts, expectedReqOpts);
         done();
       };
@@ -366,9 +362,7 @@ describe('TransactionRequest', () => {
     const TABLE = 'table-name';
     const KEYS = ['key', ['composite', 'key']];
 
-    const ENCODED_VALUE = {
-      encoded: true,
-    };
+    const ENCODED_VALUE = {kind: 'stringValue', stringValue: 'value'};
 
     const EXPECTED_MUTATION = {
       delete: {
@@ -386,12 +380,11 @@ describe('TransactionRequest', () => {
       },
     };
 
+    let stub: sinon.SinonStub;
+
     beforeEach(() => {
       transactionRequest.transaction = true;
-
-      fakeCodec.encode = () => {
-        return ENCODED_VALUE;
-      };
+      stub = sandbox.stub(codec, 'encode').returns(ENCODED_VALUE);
     });
 
     describe('non-transactional instance', () => {
@@ -460,29 +453,14 @@ describe('TransactionRequest', () => {
     });
 
     it('should correctly make and return the request', done => {
-      let numEncodeRequests = 0;
-
-      fakeCodec.encode = (key) => {
-        numEncodeRequests++;
-
-        switch (numEncodeRequests) {
-          case 1:
-            assert.strictEqual(key, KEYS[0]);
-            break;
-          case 2:
-            assert.strictEqual(key, KEYS[1][0]);
-            break;
-          case 3:
-            assert.strictEqual(key, KEYS[1][1]);
-            break;
-          default:
-            break;
-        }
-
-        return ENCODED_VALUE;
-      };
+      const expectedKeys = [KEYS[0], KEYS[1][0], KEYS[1][1]];
 
       transactionRequest.queue_ = (mutation) => {
+        expectedKeys.forEach((expectedKey, i) => {
+          const [key] = stub.getCall(i).args;
+          assert.strictEqual(key, expectedKey);
+        });
+
         assert.deepStrictEqual(mutation, EXPECTED_MUTATION);
         done();
       };
@@ -500,13 +478,6 @@ describe('TransactionRequest', () => {
     });
 
     it('should accept just a key', done => {
-      const encodedValue = {
-        encoded: true,
-      };
-      fakeCodec.encode = () => {
-        return encodedValue;
-      };
-
       transactionRequest.queue_ = (mutation) => {
         const expectedSingleMutation = extend(true, {}, EXPECTED_MUTATION);
 
@@ -698,12 +669,11 @@ describe('TransactionRequest', () => {
       ],
     };
 
+    let stub: sinon.SinonStub;
+
     beforeEach(() => {
       transactionRequest.transaction = true;
-
-      fakeCodec.encode = (value) => {
-        return value;
-      };
+      stub = sandbox.stub(codec, 'encode').callsFake(value => value);
     });
 
     describe('non-transactional instance', () => {
@@ -773,44 +743,17 @@ describe('TransactionRequest', () => {
     });
 
     it('should correctly make and return the request', done => {
-      let numEncodeRequests = 0;
-
-      fakeCodec.encode = (value) => {
-        numEncodeRequests++;
-
-        switch (numEncodeRequests) {
-          case 1:
-            assert.strictEqual(value, KEYVALS[0].anotherNullable);
-            break;
-          case 2:
-            assert.strictEqual(value, KEYVALS[0].key);
-            break;
-          case 3:
-            assert.strictEqual(value, KEYVALS[0].nonNullable);
-            break;
-          case 4:
-            assert.strictEqual(value, KEYVALS[0].nullable);
-            break;
-          case 5:
-            assert.strictEqual(value, KEYVALS[1].anotherNullable);
-            break;
-          case 6:
-            assert.strictEqual(value, KEYVALS[1].key);
-            break;
-          case 7:
-            assert.strictEqual(value, KEYVALS[1].nonNullable);
-            break;
-          case 8:
-            assert.strictEqual(value, KEYVALS[1].nullable);
-            break;
-          default:
-            break;
-        }
-
-        return value;
-      };
+      const expectedValues = [
+        KEYVALS[0].anotherNullable, KEYVALS[0].key, KEYVALS[0].nonNullable,
+        KEYVALS[0].nullable, KEYVALS[1].anotherNullable, KEYVALS[1].key,
+        KEYVALS[1].nonNullable, KEYVALS[1].nullable
+      ];
 
       transactionRequest.queue_ = mutation => {
+        expectedValues.forEach((expectedValue, i) => {
+          const [value] = stub.getCall(i).args;
+          assert.strictEqual(value, expectedValue);
+        });
         assert.deepStrictEqual(mutation, EXPECTED_MUTATION);
         done();
       };