Support for @BatchMapping methods

See gh-130

Author: rstoyanchev

spring-graphql/src/main/java/org/springframework/graphql/data/method/BatchLoadHandlerMethod.java

@@ -0,0 +1,108 @@
+/*
+ * Copyright 2002-2021 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.springframework.graphql.data.method;
+
+import java.util.Collection;
+import java.util.Map;
+
+import org.dataloader.BatchLoaderEnvironment;
+import reactor.core.publisher.Flux;
+import reactor.core.publisher.Mono;
+
+import org.springframework.core.CollectionFactory;
+import org.springframework.core.MethodParameter;
+import org.springframework.lang.Nullable;
+import org.springframework.util.Assert;
+
+/**
+ * An extension of {@link HandlerMethod} for annotated handler methods adapted
+ * to a batch loader function with a list of values and {@link BatchLoaderEnvironment}
+ * as their input.
+ *
+ * @author Rossen Stoyanchev
+ * @since 1.0.0
+ */
+public class BatchLoadHandlerMethod extends InvocableHandlerMethodSupport {
+
+
+	public BatchLoadHandlerMethod(HandlerMethod handlerMethod) {
+		super(handlerMethod);
+	}
+
+
+	/**
+	 * Invoke the underlying batch loading method, resolving its arguments from
+	 * the given keys for batch loading and the {@link BatchLoaderEnvironment}.
+	 *
+	 * @param keys the batch loading keys
+	 * @param environment the environment available to batch loaders
+	 * @return a {@code Flux} of values or a {@code Mono} with map of key-value pairs.
+	 */
+	@Nullable
+	public <K> Object invoke(Collection<K> keys, BatchLoaderEnvironment environment) {
+
+		MethodParameter[] parameters = getMethodParameters();
+		Assert.notEmpty(parameters, "Batch loading methods should have at least " +
+				"one argument with the List of parent objects: " + getBridgedMethod().toGenericString());
+
+		Object[] args = new Object[parameters.length];
+		for (int i = 0; i < parameters.length; i++) {
+			args[i] = resolveArgument(parameters[i], keys, environment);
+		}
+
+		Object result;
+		try {
+			result = doInvoke(args);
+		}
+		catch (Exception ex) {
+			throw new IllegalStateException("...", ex);
+		}
+
+		if (result != null) {
+			if (result instanceof Collection) {
+				return Flux.fromIterable((Collection<?>) result);
+			}
+			else if (result instanceof Map) {
+				return Mono.just(result);
+			}
+		}
+
+		return result;
+	}
+
+	public <K> Object resolveArgument(
+			MethodParameter parameter, Collection<K> keys, BatchLoaderEnvironment environment) {
+
+		Class<?> parameterType = parameter.getParameterType();
+
+		if (Collection.class.isAssignableFrom(parameterType)) {
+			if (parameterType.isInstance(keys)) {
+				return keys;
+			}
+			Class<?> elementType = parameter.nested().getNestedParameterType();
+			Collection<K> collection = CollectionFactory.createCollection(parameterType, elementType, keys.size());
+			collection.addAll(keys);
+			return collection;
+		}
+
+		if (parameterType.isInstance(environment)) {
+			return environment;
+		}
+
+		throw new IllegalStateException(formatArgumentError(parameter, "Unexpected argument type."));
+	}
+
+}

spring-graphql/src/main/java/org/springframework/graphql/data/method/DataFetcherHandlerMethod.java

@@ -61,7 +61,7 @@ public HandlerMethodArgumentResolverComposite getResolvers() {
 
 	/**
 	 * Invoke the method after resolving its argument values in the context of
-	 * the given environment.
+	 * the given {@link DataFetchingEnvironment}.
 	 * <p>Argument values are commonly resolved through
 	 * {@link HandlerMethodArgumentResolver HandlerMethodArgumentResolvers}.
 	 * The {@code providedArgs} parameter however may supply argument values to

spring-graphql/src/main/java/org/springframework/graphql/data/method/annotation/BatchMapping.java

@@ -0,0 +1,91 @@
+/*
+ * Copyright 2002-2021 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.springframework.graphql.data.method.annotation;
+
+import java.lang.annotation.Documented;
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+
+import org.springframework.core.annotation.AliasFor;
+
+/**
+ * Annotation for handler methods that batch load field values, given a list
+ * of source/parent values. For example:
+ *
+ * <pre class="code">
+ * &#064;BatchMapping
+ * public Flux&lt;Author&gt; author(List&lt;Book&gt; books) {
+ *     // ...
+ * }
+ * </pre>
+ *
+ * <p>The annotated method is registered as a batch loading function and along
+ * with it, a {@link graphql.schema.DataFetcher} for the field is registered
+ * transparently that looks up the field through the registered
+ * {@code DataLoader}.
+ *
+ * <p>Effectively, a shortcut for:
+ *
+ * <pre class="code">
+ * &#064;Controller
+ * public class BookController {
+ *
+ *     public BookController(BatchLoaderRegistry registry) {
+ *         registry.forTypePair(Long.class, Author.class).registerBatchLoader((ids, env) -> ...);
+ *     }
+ *
+ *     &#064;SchemaMapping
+ *     public Author author(Book book, DataLoader&lt;Long, Author&gt; dataLoader) {
+ *         return dataLoader.load(book.getAuthorId());
+ *     }
+ *
+ * }
+ * </pre>
+ *
+ * @author Rossen Stoyanchev
+ * @since 1.0.0
+ */
+@Target({ElementType.TYPE, ElementType.METHOD})
+@Retention(RetentionPolicy.RUNTIME)
+@Documented
+public @interface BatchMapping {
+
+	/**
+	 * Customize the name of the GraphQL field to bind to.
+	 * <p>By default, if not specified, this is initialized from the method name.
+	 */
+	@AliasFor("value")
+	String field() default "";
+
+	/**
+	 * Effectively an alias for {@link #field()}.
+	 */
+	@AliasFor("field")
+	String value() default "";
+
+	/**
+	 * Customizes the name of the parent/container type for the GraphQL field.
+	 * <p>By default, if not specified, it is derived from the class name of the
+	 * List of source/parent values injected into the handler method.
+	 * <p>This value for this attribute can be initialized from a class-level
+	 * {@link SchemaMapping @SchemaMapping}. When used on both levels, the one
+	 * on the method level overrides the one at the class level.
+	 */
+	String typeName() default "";
+
+}