Support DataFetchingFieldSelectionSet as an argument

spring-graphql-docs/src/docs/asciidoc/index.adoc

@@ -553,6 +553,10 @@ See <<controllers-schema-mapping-data-loader>>.
 | For access to the context from the `DataFetchingEnvironment`.
 See <<controllers-schema-mapping-graphql-context>>.
 
+| `DataFetchingFieldSelectionSet`
+| For access to the selection set for the query through the `DataFetchingEnvironment`.
+See <<controllers-schema-mapping-selection-set>>.
+
 | `DataFetchingEnvironment`
 | For direct access to the underlying `DataFetchingEnvironment`.
 See <<controllers-schema-mapping-environment>>.
@@ -682,6 +686,14 @@ To access the `GraphQLContext` from the `DataFetchingEnvironment`, declare a met
 parameter of the same type.
 
 
+[[controllers-schema-mapping-selection-set]]
+==== `DataFetchingFieldSelectionSet`
+
+To access the `DataFetchingFieldSelectionSet` from the `DataFetchingEnvironment`, declare
+a method parameter of the same type. This is useful to peek ahead at the fields that need
+to be fetched.
+
+
 [[controllers-schema-mapping-environment]]
 ==== `DataFetchingEnvironment`
 

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

@@ -17,12 +17,14 @@ package org.springframework.graphql.data.method.annotation.support;
 
 import graphql.GraphQLContext;
 import graphql.schema.DataFetchingEnvironment;
+import graphql.schema.DataFetchingFieldSelectionSet;
 
 import org.springframework.core.MethodParameter;
 import org.springframework.graphql.data.method.HandlerMethodArgumentResolver;
 
 /**
- * Resolver for {@link DataFetchingEnvironment} or {@link GraphQLContext} arguments.
+ * Resolver for {@link DataFetchingEnvironment} as well as arguments of type
+ * {@link GraphQLContext} or {@link DataFetchingFieldSelectionSet}.
  *
  * @author Rossen Stoyanchev
  * @since 1.0.0
@@ -32,7 +34,8 @@ public class DataFetchingEnvironmentMethodArgumentResolver implements HandlerMet
 	@Override
 	public boolean supportsParameter(MethodParameter parameter) {
 		Class<?> type = parameter.getParameterType();
-		return (type.equals(DataFetchingEnvironment.class) || type.equals(GraphQLContext.class));
+		return (type.equals(DataFetchingEnvironment.class) || type.equals(GraphQLContext.class) ||
+				type.equals(DataFetchingFieldSelectionSet.class));
 	}
 
 	@Override
@@ -41,9 +44,15 @@ public class DataFetchingEnvironmentMethodArgumentResolver implements HandlerMet
 		if (type.equals(GraphQLContext.class)) {
 			return environment.getGraphQlContext();
 		}
-		else {
+		else if (type.equals(DataFetchingFieldSelectionSet.class)) {
+			return environment.getSelectionSet();
+		}
+		else if (type.equals(DataFetchingEnvironment.class)) {
 			return environment;
 		}
+		else {
+			throw new IllegalStateException("Unexpected method parameter type: " + parameter);
+		}
 	}
 
 }