Add distinctOn to QueryBuilder

packages/graphile-build-pg/src/QueryBuilder.d.ts

@@ -51,6 +51,7 @@ export default class QueryBuilder {
   public offset(offsetGen: NumberGen): void;
   public first(first: number): void;
   public last(last: number): void;
+  public distinctOn(exprGen: SQLGen): void;
 
   // ----------------------------------------
 

packages/graphile-build-pg/src/QueryBuilder.js

@@ -3,6 +3,7 @@ import * as sql from "pg-sql2";
 import type { SQL } from "pg-sql2";
 import isSafeInteger from "lodash/isSafeInteger";
 import chunk from "lodash/chunk";
+import isEqual from "lodash/isEqual";
 import type { PgClass, PgType } from "./plugins/PgIntrospectionPlugin";
 
 // eslint-disable-next-line flowtype/no-weak-types
@@ -106,6 +107,7 @@ class QueryBuilder {
     offset: ?NumberGen,
     first: ?number,
     last: ?number,
+    distinctOn: Array<SQLGen>,
     beforeLock: {
       [string]: Array<() => void> | null,
     },
@@ -133,6 +135,7 @@ class QueryBuilder {
     offset: ?number,
     first: ?number,
     last: ?number,
+    distinctOn: Array<SQLGen>,
     cursorComparator: ?CursorComparator,
   };
   lockContext: {
@@ -170,6 +173,7 @@ class QueryBuilder {
       last: false,
       limit: false,
       offset: false,
+      distinctOn: false,
     };
     this.finalized = false;
     this.selectedIdentifiers = false;
@@ -192,6 +196,7 @@ class QueryBuilder {
       offset: null,
       first: null,
       last: null,
+      distinctOn: [],
       beforeLock: {
         // As a performance optimisation, we're going to list a number of lock
         // types so that V8 doesn't need to mutate the object too much
@@ -231,6 +236,7 @@ class QueryBuilder {
       offset: null,
       first: null,
       last: null,
+      distinctOn: [],
       cursorComparator: null,
     };
     this._children = new Map();
@@ -511,6 +517,10 @@ ${sql.join(
     }
     this.data.last = last;
   }
+  distinctOn(exprGen: SQLGen) {
+    this.checkLock("distinctOn");
+    this.data.distinctOn.push(exprGen);
+  }
 
   // ----------------------------------------
 
@@ -744,7 +754,15 @@ ${sql.join(
         : this.buildSelectFields();
 
     let fragment = sql.fragment`\
-select ${useAsterisk ? sql.fragment`${this.getTableAlias()}.*` : fields}
+select ${
+      this.compiledData.distinctOn.length
+      ? sql.fragment`distinct on (${sql.join(
+          this.compiledData.distinctOn,
+          ", "
+        )})`
+      : sql.blank
+    }
+${useAsterisk ? sql.fragment`${this.getTableAlias()}.*` : fields}
 ${
   this.compiledData.from &&
   sql.fragment`from ${this.compiledData.from[0]} as ${this.getTableAlias()}`
@@ -868,11 +886,16 @@ order by (row_number() over (partition by 1)) desc`; /* We don't need to factor
       this.locks[type] = isDev ? new Error("Initally locked here").stack : true;
       this.compiledData[type] = data;
     } else if (type === "orderBy") {
-      this.compiledData[type] = this.data[type].map(([a, b, c]) => [
-        callIfNecessary(a, context),
-        b,
-        c,
-      ]);
+      // Add distinct to existing order by to avoid `SELECT DISTINCT ON expressions must match initial ORDER BY expressions`
+      // Convert distinct fields to order by applying ascending and using existing order by for matching fields
+      const distinctAsOrderBy = this.data["distinctOn"].map(
+        d => this.data[type].find(([a]) => isEqual(a, d)) ?? [d, true, null]
+      );
+
+      // Create a union of the distinct and order by fields
+      this.compiledData[type] = [
+        ...new Set([...distinctAsOrderBy, ...this.data[type]]),
+      ].map(([a, b, c]) => [callIfNecessary(a, context), b, c]);
     } else if (type === "from") {
       if (this.data.from) {
         const f = this.data.from;
@@ -894,6 +917,8 @@ order by (row_number() over (partition by 1)) desc`; /* We don't need to factor
       this.compiledData[type] = this.data[type];
     } else if (type === "last") {
       this.compiledData[type] = this.data[type];
+    } else if (type === "distinctOn") {
+      this.compiledData[type] = callIfNecessaryArray(this.data[type], context);
     } else {
       throw new Error(`Wasn't expecting to lock '${type}'`);
     }
@@ -925,6 +950,7 @@ order by (row_number() over (partition by 1)) desc`; /* We don't need to factor
     this.lock("limit");
     this.lock("first");
     this.lock("last");
+    this.lock("distinctOn");
     // We must execute select after orderBy otherwise we cannot generate a cursor
     this.lock("fixedSelectExpression");
     this.lock("selectCursor");

packages/postgraphile-core/__tests__/helpers-v5.js

@@ -24,6 +24,7 @@ import { withPgClient, getServerVersionNum } from "./helpers";
 import jsonwebtoken from "jsonwebtoken";
 import { createPostGraphileSchema } from "..";
 import { makeExtendSchemaPlugin, gql } from "graphile-utils";
+import DistinctOnPlugin from "./integration/DistinctOnPlugin";
 import ToyCategoriesPlugin from "./integration/ToyCategoriesPlugin";
 
 /**
@@ -468,6 +469,7 @@ const makeSchema = config => {
         appendPlugins: [
           ExtendedPlugin,
           config.ToyCategoriesPlugin ? ToyCategoriesPlugin : null,
+          config.DistinctOnPlugin ? DistinctOnPlugin : null,
         ].filter(isNotNullish),
       }
     );

packages/postgraphile-core/__tests__/integration/DistinctOnPlugin.js

@@ -0,0 +1,45 @@
+module.exports = builder => {
+  builder.hook(
+    "GraphQLObjectType:fields:field:args",
+    (args, build, context) => {
+      const {
+        graphql: { GraphQLString, GraphQLList },
+        pgSql: sql,
+      } = build;
+
+      const {
+        Self,
+        scope: { fieldName },
+        addArgDataGenerator,
+      } = context;
+
+      if (!(Self.name === "Query" && fieldName === "allToys")) {
+        return args;
+      }
+
+      addArgDataGenerator(({ distinct }) => {
+        return {
+          pgQuery: queryBuilder => {
+            distinct?.map(field => {
+              const id = sql.fragment`${queryBuilder.getTableAlias()}.${sql.identifier(
+                field
+              )}`;
+
+              queryBuilder.distinctOn(id);
+            });
+          },
+        };
+      });
+
+      return build.extend(
+        args,
+        {
+          distinct: {
+            type: new GraphQLList(GraphQLString),
+          },
+        },
+        "test"
+      );
+    }
+  );
+};

packages/postgraphile-core/__tests__/kitchen-sink-data.sql

@@ -276,6 +276,13 @@ insert into named_query_builder.toy_categories(toy_id, category_id, approved) va
   (4, 2, true),
   (1, 3, false);
 
+
+insert into distinct_query_builder.toys (id, name, color) values
+  (1, 'Rex', 'green'),
+  (2, 'Toy Soldiers', 'green'),
+  (3, 'Dino-Rocket Launcher', 'red'),
+  (4, 'History of Dinosaurs book', 'red');
+
 --------------------------------------------------------------------------------
 alter sequence enum_tables.letter_descriptions_id_seq restart with 101;
 insert into enum_tables.letter_descriptions(letter, letter_via_view, description) values

packages/postgraphile-core/__tests__/kitchen-sink-schema.sql

@@ -13,6 +13,7 @@ drop schema if exists
   large_bigint,
   network_types,
   named_query_builder,
+  distinct_query_builder,
   enum_tables,
   geometry
 cascade;
@@ -1140,6 +1141,16 @@ create table named_query_builder.toy_categories (
 
 --------------------------------------------------------------------------------
 
+create schema distinct_query_builder;
+
+create table distinct_query_builder.toys (
+  id serial primary key,
+  name text not null,
+  color text not null
+);
+
+--------------------------------------------------------------------------------
+
 create schema enum_tables;
 create table enum_tables.abcd (letter text primary key, description text);
 comment on column enum_tables.abcd.description is E'@enumDescription';

packages/postgraphile-core/__tests__/queries/base/distinct_query_builder.toys.json5

@@ -0,0 +1,46 @@
+{
+  t1: {
+    nodes: [
+      {
+        name: "Rex",
+        color: "green",
+      },
+      {
+        name: "Dino-Rocket Launcher",
+        color: "red",
+      },
+    ],
+  },
+  t2: {
+    nodes: [
+      {
+        name: "Rex",
+      },
+      {
+        name: "Toy Soldiers",
+      },
+      {
+        name: "Dino-Rocket Launcher",
+      },
+      {
+        name: "History of Dinosaurs book",
+      },
+    ],
+  },
+  t3: {
+    nodes: [
+      {
+        name: "Rex",
+      },
+      {
+        name: "Toy Soldiers",
+      },
+      {
+        name: "Dino-Rocket Launcher",
+      },
+      {
+        name: "History of Dinosaurs book",
+      },
+    ],
+  },
+}

packages/postgraphile-core/__tests__/queries/base/distinct_query_builder.toys.sql

@@ -0,0 +1,102 @@
+with __local_0__ as (
+  select to_json(
+    (
+      json_build_object(
+        '__identifiers'::text,
+        json_build_array(__local_1__."id"),
+        'name'::text,
+        (__local_1__."name"),
+        'color'::text,
+        (__local_1__."color")
+      )
+    )
+  ) as "@nodes"
+  from (
+    select distinct on (__local_1__."color") __local_1__.*
+    from "distinct_query_builder"."toys" as __local_1__
+    where (TRUE) and (TRUE)
+    order by __local_1__."color" ASC,
+    __local_1__."id" ASC
+  ) __local_1__
+),
+__local_2__ as (
+  select json_agg(
+    to_json(__local_0__)
+  ) as data
+  from __local_0__
+)
+select coalesce(
+  (
+    select __local_2__.data
+    from __local_2__
+  ),
+  '[]'::json
+) as "data"
+
+with __local_0__ as (
+  select to_json(
+    (
+      json_build_object(
+        '__identifiers'::text,
+        json_build_array(__local_1__."id"),
+        'name'::text,
+        (__local_1__."name")
+      )
+    )
+  ) as "@nodes"
+  from (
+    select distinct on (
+      __local_1__."id",
+      __local_1__."name"
+    ) __local_1__.*
+    from "distinct_query_builder"."toys" as __local_1__
+    where (TRUE) and (TRUE)
+    order by __local_1__."id" ASC,
+    __local_1__."name" ASC
+  ) __local_1__
+),
+__local_2__ as (
+  select json_agg(
+    to_json(__local_0__)
+  ) as data
+  from __local_0__
+)
+select coalesce(
+  (
+    select __local_2__.data
+    from __local_2__
+  ),
+  '[]'::json
+) as "data"
+
+with __local_0__ as (
+  select to_json(
+    (
+      json_build_object(
+        '__identifiers'::text,
+        json_build_array(__local_1__."id"),
+        'name'::text,
+        (__local_1__."name")
+      )
+    )
+  ) as "@nodes"
+  from (
+    select __local_1__.*
+    from "distinct_query_builder"."toys" as __local_1__
+    where (TRUE) and (TRUE)
+    order by __local_1__."id" ASC
+  ) __local_1__
+),
+__local_2__ as (
+  select json_agg(
+    to_json(__local_0__)
+  ) as data
+  from __local_0__
+)
+select coalesce(
+  (
+    select __local_2__.data
+    from __local_2__
+  ),
+  '[]'::json
+) as "data"

packages/postgraphile-core/__tests__/queries/base/distinct_query_builder.toys.test.graphql

@@ -0,0 +1,22 @@
+## expect(errors).toBeFalsy();
+#> schema: ["distinct_query_builder"]
+#> subscriptions: true
+#> DistinctOnPlugin: true
+{
+  t1: allToys(distinct: ["color"]) {
+    nodes {
+      name
+      color
+    }
+  }
+  t2: allToys(distinct: ["id", "name"]) {
+    nodes {
+      name
+    }
+  }
+  t3: allToys {
+    nodes {
+      name
+    }
+  }
+}