Perform hasDataLoaderRegistrations check at runtime

Closes gh-1020

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2021 the original author or authors.
+ * Copyright 2002-2024 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.
@@ -30,6 +30,17 @@ import org.dataloader.DataLoaderRegistry;
  */
 public interface DataLoaderRegistrar {
 
+
+	/**
+	 * Whether the registrar has any {@code DataLoader} registrations to make.
+	 * @since 1.2.8
+	 */
+	default boolean hasRegistrations() {
+		DataLoaderRegistry registry = DataLoaderRegistry.newRegistry().build();
+		registerDataLoaders(registry, GraphQLContext.newContext().build());
+		return !registry.getDataLoaders().isEmpty();
+	}
+
 	/**
 	 * Callback that provides access to the {@link DataLoaderRegistry} from the
 	 * the {@link graphql.ExecutionInput}.

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

@@ -90,6 +90,11 @@ public class DefaultBatchLoaderRegistry implements BatchLoaderRegistry {
 		return new DefaultRegistrationSpec<>(name);
 	}
 
+	@Override
+	public boolean hasRegistrations() {
+		return (!this.loaders.isEmpty() || !this.mappedLoaders.isEmpty());
+	}
+
 	@Override
 	public void registerDataLoaders(DataLoaderRegistry registry, GraphQLContext context) {
 		BatchLoaderContextProvider contextProvider = () -> context;

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

@@ -34,6 +34,7 @@ import org.springframework.graphql.ExecutionGraphQlRequest;
 import org.springframework.graphql.ExecutionGraphQlResponse;
 import org.springframework.graphql.ExecutionGraphQlService;
 import org.springframework.graphql.support.DefaultExecutionGraphQlResponse;
+import org.springframework.lang.Nullable;
 import org.springframework.util.ClassUtils;
 import org.springframework.util.ReflectionUtils;
 
@@ -57,7 +58,8 @@ public class DefaultExecutionGraphQlService implements ExecutionGraphQlService {
 
 	private final List<DataLoaderRegistrar> dataLoaderRegistrars = new ArrayList<>();
 
-	private boolean hasDataLoaderRegistrations;
+	@Nullable
+	private Boolean hasDataLoaderRegistrations;
 
 	private final boolean isDefaultExecutionIdProvider;
 
@@ -80,13 +82,6 @@ public class DefaultExecutionGraphQlService implements ExecutionGraphQlService {
 	 */
 	public void addDataLoaderRegistrar(DataLoaderRegistrar registrar) {
 		this.dataLoaderRegistrars.add(registrar);
-		this.hasDataLoaderRegistrations = (this.hasDataLoaderRegistrations || hasRegistrations(registrar));
-	}
-
-	private static boolean hasRegistrations(DataLoaderRegistrar registrar) {
-		DataLoaderRegistry registry = DataLoaderRegistry.newRegistry().build();
-		registrar.registerDataLoaders(registry, GraphQLContext.newContext().build());
-		return !registry.getDataLoaders().isEmpty();
 	}
 
 
@@ -104,28 +99,41 @@ public class DefaultExecutionGraphQlService implements ExecutionGraphQlService {
 			ContextSnapshotFactoryHelper.saveInstance(factory, graphQLContext);
 			factory.captureFrom(contextView).updateContext(graphQLContext);
 
-			ExecutionInput updatedExecutionInput =
-					(this.hasDataLoaderRegistrations ? registerDataLoaders(executionInput) : executionInput);
+			ExecutionInput executionInputToUse = registerDataLoaders(executionInput);
 
-			return Mono.fromFuture(this.graphQlSource.graphQl().executeAsync(updatedExecutionInput))
-					.map((result) -> new DefaultExecutionGraphQlResponse(updatedExecutionInput, result));
+			return Mono.fromFuture(this.graphQlSource.graphQl().executeAsync(executionInputToUse))
+					.map((result) -> new DefaultExecutionGraphQlResponse(executionInputToUse, result));
 		});
 	}
 
 	private ExecutionInput registerDataLoaders(ExecutionInput executionInput) {
-		GraphQLContext graphQLContext = executionInput.getGraphQLContext();
-		DataLoaderRegistry existingRegistry = executionInput.getDataLoaderRegistry();
-		if (existingRegistry == this.emptyDataLoaderRegistryInstance) {
-			DataLoaderRegistry newRegistry = DataLoaderRegistry.newRegistry().build();
-			applyDataLoaderRegistrars(newRegistry, graphQLContext);
-			executionInput = executionInput.transform((builder) -> builder.dataLoaderRegistry(newRegistry));
+		if (this.hasDataLoaderRegistrations == null) {
+			this.hasDataLoaderRegistrations = initHasDataLoaderRegistrations();
 		}
-		else {
-			applyDataLoaderRegistrars(existingRegistry, graphQLContext);
+		if (this.hasDataLoaderRegistrations) {
+			GraphQLContext graphQLContext = executionInput.getGraphQLContext();
+			DataLoaderRegistry existingRegistry = executionInput.getDataLoaderRegistry();
+			if (existingRegistry == this.emptyDataLoaderRegistryInstance) {
+				DataLoaderRegistry newRegistry = DataLoaderRegistry.newRegistry().build();
+				applyDataLoaderRegistrars(newRegistry, graphQLContext);
+				executionInput = executionInput.transform((builder) -> builder.dataLoaderRegistry(newRegistry));
+			}
+			else {
+				applyDataLoaderRegistrars(existingRegistry, graphQLContext);
+			}
 		}
 		return executionInput;
 	}
 
+	private boolean initHasDataLoaderRegistrations() {
+		for (DataLoaderRegistrar registrar : this.dataLoaderRegistrars) {
+			if (registrar.hasRegistrations()) {
+				return true;
+			}
+		}
+		return false;
+	}
+
 	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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2023 the original author or authors.
+ * Copyright 2002-2024 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.
@@ -41,26 +41,27 @@ 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();
 
+		BatchLoaderRegistry batchLoaderRegistry = new DefaultBatchLoaderRegistry();
 		DefaultExecutionGraphQlService graphQlService = new DefaultExecutionGraphQlService(graphQlSource);
 		graphQlService.addDataLoaderRegistrar(batchLoaderRegistry);
 
-		DataLoaderRegistry myRegistry = new DataLoaderRegistry();
+		// gh-1020: register loader after adding the registry to DefaultExecutionGraphQlService
+		batchLoaderRegistry.forTypePair(Book.class, Author.class)
+				.registerBatchLoader((books, batchLoaderEnvironment) -> Flux.empty());
+
+		DataLoaderRegistry dataLoaderRegistry = new DataLoaderRegistry();
 
 		ExecutionGraphQlRequest request = TestExecutionRequest.forDocument("{ greeting }");
-		request.configureExecutionInput((input, builder) -> builder.dataLoaderRegistry(myRegistry).build());
+		request.configureExecutionInput((input, builder) -> builder.dataLoaderRegistry(dataLoaderRegistry).build());
 
 		ExecutionGraphQlResponse response = graphQlService.execute(request).block();
 		Map<?, ?> data = response.getExecutionResult().getData();
 		assertThat(data).isEqualTo(Map.of("greeting", "hi"));
-		assertThat(myRegistry.getDataLoaders()).hasSize(1);
+		assertThat(dataLoaderRegistry.getDataLoaders()).hasSize(1);
 	}
 
 }