Make it clearer which fields are required when building a DynamoDB En…

…hanced Client WriteBatch. Currently, a NullPointerException is thrown if you forget to call the builder with mappedTableResource(MappedTableResource<T>)

.changes/next-release/bugfix-AmazonDynamoDBEnhancedClient-8e7d838.json

@@ -0,0 +1,6 @@
+{
+    "type": "bugfix",
+    "category": "Amazon DynamoDB Enhanced Client",
+    "contributor": "swar8080",
+    "description": "Make it clearer which fields are required when building a WriteBatch, which helps avoid NullPointerExceptions when adding a putItem or deleteItem to the batch"
+}

services-custom/dynamodb-enhanced/src/main/java/software/amazon/awssdk/enhanced/dynamodb/model/WriteBatch.java

@@ -53,15 +53,31 @@ private WriteBatch(BuilderImpl<?> builder) {
         this.writeRequests = getItemsFromSupplier(builder.itemSupplierList);
     }
 
+    /**
+     * Creates a newly initialized builder for a write batch.
+     *
+     * @param itemClass the class that items in this table map to
+     * @param mappedTableResource the mapped table resource (table) that the items in this write batch should come from
+     * @param <T> The type of the modelled object to be written in this batch
+     * @return a WriteBatch builder
+     */
+    public static <T> Builder<T> builder(Class<? extends T> itemClass, MappedTableResource<T> mappedTableResource) {
+        return new BuilderImpl<>(itemClass, mappedTableResource);
+    }
+
     /**
      * Creates a newly initialized builder for a write batch.
      *
      * @param itemClass the class that items in this table map to
      * @param <T> The type of the modelled object, corresponding to itemClass
      * @return a WriteBatch builder
+     *
+     * @deprecated Use {@link WriteBatch#builder(Class, MappedTableResource)} to ensure the {@link WriteBatch} is built
+     * with the required fields.
      */
+    @Deprecated
     public static <T> Builder<T> builder(Class<? extends T> itemClass) {
-        return new BuilderImpl<>(itemClass);
+        return builder(itemClass, null);
     }
 
     /**
@@ -192,8 +208,9 @@ private static final class BuilderImpl<T> implements Builder<T> {
         private List<Supplier<WriteRequest>> itemSupplierList = new ArrayList<>();
         private MappedTableResource<T> mappedTableResource;
 
-        private BuilderImpl(Class<? extends T> itemClass) {
+        private BuilderImpl(Class<? extends T> itemClass, MappedTableResource<T> mappedTableResource) {
             this.itemClass = itemClass;
+            this.mappedTableResource = mappedTableResource;
         }
 
         @Override

services-custom/dynamodb-enhanced/src/test/java/software/amazon/awssdk/enhanced/dynamodb/model/WriteBatchTest.java

@@ -55,6 +55,14 @@ public void setupMappedTables() {
 
     @Test
     public void builder_minimal() {
+        WriteBatch builtObject = WriteBatch.builder(FakeItem.class, fakeItemMappedTable).build();
+
+        assertThat(builtObject.tableName(), is(TABLE_NAME));
+        assertThat(builtObject.writeRequests(), is(nullValue()));
+    }
+
+    @Test
+    public void builder_minimal_deprecated() {
         WriteBatch builtObject = WriteBatch.builder(FakeItem.class).build();
 
         assertThat(builtObject.tableName(), is(nullValue()));
@@ -65,6 +73,22 @@ public void builder_minimal() {
     public void builder_maximal_consumer_style() {
         FakeItem fakeItem = createUniqueFakeItem();
 
+        WriteBatch builtObject = WriteBatch.builder(FakeItem.class, fakeItemMappedTable)
+                                           .addPutItem(r -> r.item(fakeItem))
+                                           .addDeleteItem(r -> r.key(k -> k.partitionValue(fakeItem.getId())))
+                                           .build();
+
+        Map<String, AttributeValue> fakeItemMap = FakeItem.getTableSchema().itemToMap(fakeItem,
+                                                                                      FakeItem.getTableMetadata().primaryKeys());
+
+        assertThat(builtObject.tableName(), is(TABLE_NAME));
+        assertThat(builtObject.writeRequests(), containsInAnyOrder(putRequest(fakeItemMap), deleteRequest(fakeItemMap)));
+    }
+
+    @Test
+    public void builder_maximal_consumer_style_deprecated() {
+        FakeItem fakeItem = createUniqueFakeItem();
+
         WriteBatch builtObject = WriteBatch.builder(FakeItem.class)
                                            .mappedTableResource(fakeItemMappedTable)
                                            .addPutItem(r -> r.item(fakeItem))
@@ -82,6 +106,27 @@ public void builder_maximal_consumer_style() {
     public void builder_maximal_builder_style() {
         FakeItem fakeItem = createUniqueFakeItem();
 
+        PutItemEnhancedRequest<FakeItem> putItem = PutItemEnhancedRequest.builder(FakeItem.class).item(fakeItem).build();
+        DeleteItemEnhancedRequest deleteItem = DeleteItemEnhancedRequest.builder()
+                                                                        .key(k -> k.partitionValue(fakeItem.getId()))
+                                                                        .build();
+
+        WriteBatch builtObject = WriteBatch.builder(FakeItem.class, fakeItemMappedTable)
+                                           .addPutItem(putItem)
+                                           .addDeleteItem(deleteItem)
+                                           .build();
+
+        Map<String, AttributeValue> fakeItemMap = FakeItem.getTableSchema().itemToMap(fakeItem,
+                                                                                      FakeItem.getTableMetadata().primaryKeys());
+
+        assertThat(builtObject.tableName(), is(TABLE_NAME));
+        assertThat(builtObject.writeRequests(), containsInAnyOrder(putRequest(fakeItemMap), deleteRequest(fakeItemMap)));
+    }
+
+    @Test
+    public void builder_maximal_builder_style_deprecated() {
+        FakeItem fakeItem = createUniqueFakeItem();
+
         PutItemEnhancedRequest<FakeItem> putItem = PutItemEnhancedRequest.builder(FakeItem.class).item(fakeItem).build();
         DeleteItemEnhancedRequest deleteItem = DeleteItemEnhancedRequest.builder()
                                                                         .key(k -> k.partitionValue(fakeItem.getId()))