Flexible creation of graphql.relay.Connection

Closes gh-1343

Author: rstoyanchev

spring-graphql/src/main/java/org/springframework/graphql/data/pagination/CompositeConnectionAdapter.java

@@ -24,17 +24,17 @@
 import org.springframework.util.Assert;
 
 /**
- * {@link ConnectionAdapter} that contains a list of others adapter, looks for
- * the first one that supports a given Object container type, and delegates to it.
+ * {@link ConnectionAdapter} that wraps a list of other adapters, and delegates
+ * to the one that supports a given type of Object container.
  *
  * @author Rossen Stoyanchev
  */
-final class CompositeConnectionAdapter implements ConnectionAdapter {
+public class CompositeConnectionAdapter implements ConnectionAdapter {
 
 	private final List<ConnectionAdapter> adapters;
 
 
-	CompositeConnectionAdapter(List<ConnectionAdapter> adapters) {
+	public CompositeConnectionAdapter(List<ConnectionAdapter> adapters) {
 		Assert.notEmpty(adapters, "ConnectionAdapter's are required");
 		this.adapters = adapters;
 	}

spring-graphql/src/main/java/org/springframework/graphql/data/pagination/ConnectionAdapter.java

@@ -19,8 +19,12 @@
 import java.util.Collection;
 import java.util.List;
 
+import graphql.relay.DefaultConnection;
+import graphql.relay.Edge;
+import graphql.relay.PageInfo;
+
 /**
- * Contract to adapt a container object for a window of elements from a larger
+ * Contract to adapt any representation of a subset of elements from a larger
  * result set to {@link graphql.relay.Connection}.
  *
  * @author Rossen Stoyanchev
@@ -60,6 +64,22 @@ public interface ConnectionAdapter {
 	 */
 	String cursorAt(Object container, int index);
 
+	/**
+	 * Create the {@link graphql.relay.Connection}.
+	 * <p>The relay spec says that a Connection may have additional fields
+	 * related to the connection, and this method allows adapter
+	 * implementations to create such an extended Connection.
+	 * <p>By default, {@link DefaultConnection} is created.
+	 * @param container the underlying container of elements
+	 * @param edges the adapted edges to use
+	 * @param pageInfo the page info for the connection
+	 * @param <T> the type edge node
+	 * @since 2.0
+	 */
+	default <T> Object createConnection(Object container, List<Edge<T>> edges, PageInfo pageInfo) {
+		return new DefaultConnection<>(edges, pageInfo);
+	}
+
 
 	/**
 	 * Create a composite {@link ConnectionAdapter} that checks which adapter

spring-graphql/src/main/java/org/springframework/graphql/data/pagination/ConnectionFieldTypeVisitor.java

@@ -182,7 +182,18 @@ private static boolean isConnectionField(GraphQLFieldDefinition field) {
 	 */
 	public static ConnectionFieldTypeVisitor create(List<ConnectionAdapter> adapters) {
 		Assert.notEmpty(adapters, "Expected at least one ConnectionAdapter");
-		return new ConnectionFieldTypeVisitor(ConnectionAdapter.from(adapters));
+		return create(ConnectionAdapter.from(adapters));
+	}
+
+	/**
+	 * Variant of {@link #create(List)} with a single adapter. This may be used
+	 * with a custom {@link CompositeConnectionAdapter}.
+	 * @param adapter the adapter to use
+	 * @return the type visitor
+	 * @since 2.0
+	 */
+	public static ConnectionFieldTypeVisitor create(ConnectionAdapter adapter) {
+		return new ConnectionFieldTypeVisitor(adapter);
 	}
 
 
@@ -266,7 +277,7 @@ private Object adaptDataFetcherResult(Object value) {
 					edges.get(0).getCursor(), edges.get(edges.size() - 1).getCursor(),
 					this.adapter.hasPrevious(container), this.adapter.hasNext(container));
 
-			return new DefaultConnection<>(edges, pageInfo);
+			return this.adapter.createConnection(container, edges, pageInfo);
 		}
 
 		private boolean isConnectionTypeNullable() {