Allow custom DataLoaderRegistry

Closes gh-836

spring-graphql/src/main/java/org/springframework/graphql/execution/DefaultExecutionGraphQlService.java

@@ -24,6 +24,7 @@
 import graphql.GraphQL;
 import graphql.GraphQLContext;
 import graphql.execution.ExecutionIdProvider;
+import graphql.execution.instrumentation.dataloader.DataLoaderDispatcherInstrumentationState;
 import io.micrometer.context.ContextSnapshot;
 import org.dataloader.DataLoaderRegistry;
 import reactor.core.publisher.Mono;
@@ -88,12 +89,21 @@ public final Mono<ExecutionGraphQlResponse> execute(ExecutionGraphQlRequest requ
 	private ExecutionInput registerDataLoaders(ExecutionInput executionInput) {
 		if (!this.dataLoaderRegistrars.isEmpty()) {
 			GraphQLContext graphQLContext = executionInput.getGraphQLContext();
-			DataLoaderRegistry previousRegistry = executionInput.getDataLoaderRegistry();
-			DataLoaderRegistry newRegistry = DataLoaderRegistry.newRegistry().registerAll(previousRegistry).build();
-			this.dataLoaderRegistrars.forEach(registrar -> registrar.registerDataLoaders(newRegistry, graphQLContext));
-			executionInput = executionInput.transform(builder -> builder.dataLoaderRegistry(newRegistry));
+			DataLoaderRegistry existingRegistry = executionInput.getDataLoaderRegistry();
+			if (existingRegistry == DataLoaderDispatcherInstrumentationState.EMPTY_DATALOADER_REGISTRY) {
+				DataLoaderRegistry newRegistry = DataLoaderRegistry.newRegistry().build();
+				applyDataLoaderRegistrars(newRegistry, graphQLContext);
+				executionInput = executionInput.transform(builder -> builder.dataLoaderRegistry(newRegistry));
+			}
+			else {
+				applyDataLoaderRegistrars(existingRegistry, graphQLContext);
+			}
 		}
 		return executionInput;
 	}
 
+	private void applyDataLoaderRegistrars(DataLoaderRegistry registry, GraphQLContext graphQLContext) {
+		this.dataLoaderRegistrars.forEach(registrar -> registrar.registerDataLoaders(registry, graphQLContext));
+	}
+
 }

spring-graphql/src/test/java/org/springframework/graphql/execution/DefaultExecutionGraphQlServiceTests.java

@@ -0,0 +1,66 @@
+/*
+ * Copyright 2002-2023 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.execution;
+
+import java.util.Map;
+
+import org.dataloader.DataLoaderRegistry;
+import org.junit.jupiter.api.Test;
+import reactor.core.publisher.Flux;
+
+import org.springframework.graphql.Author;
+import org.springframework.graphql.Book;
+import org.springframework.graphql.ExecutionGraphQlRequest;
+import org.springframework.graphql.ExecutionGraphQlResponse;
+import org.springframework.graphql.GraphQlSetup;
+import org.springframework.graphql.TestExecutionRequest;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Unit tests for {@link DefaultExecutionGraphQlService}.
+ *
+ * @author Rossen Stoyanchev
+ * @since 1.2.4
+ */
+public class DefaultExecutionGraphQlServiceTests {
+
+	@Test
+	void customDataLoaderRegistry() {
+		DefaultBatchLoaderRegistry batchLoaderRegistry = new DefaultBatchLoaderRegistry();
+		batchLoaderRegistry.forTypePair(Book.class, Author.class)
+				.registerBatchLoader((books, batchLoaderEnvironment) -> Flux.empty());
+
+		GraphQlSource graphQlSource = GraphQlSetup.schemaContent("type Query { greeting: String }")
+				.queryFetcher("greeting", (env) -> "hi")
+				.toGraphQlSource();
+
+		DefaultExecutionGraphQlService graphQlService = new DefaultExecutionGraphQlService(graphQlSource);
+		graphQlService.addDataLoaderRegistrar(batchLoaderRegistry);
+
+		DataLoaderRegistry myRegistry = new DataLoaderRegistry();
+
+		ExecutionGraphQlRequest request = TestExecutionRequest.forDocument("{ greeting }");
+		request.configureExecutionInput((input, builder) -> builder.dataLoaderRegistry(myRegistry).build());
+
+		ExecutionGraphQlResponse response = graphQlService.execute(request).block();
+		Map<?, ?> data = response.getExecutionResult().getData();
+		assertThat(data).isEqualTo(Map.of("greeting", "hi"));
+		assertThat(myRegistry.getDataLoaders()).hasSize(1);
+	}
+
+}