fix(GraphQL):This PR allows to use fragments on interfaces while querying other interface.

graphql/e2e/common/fragment.go

@@ -169,6 +169,20 @@ func fragmentInQueryOnInterface(t *testing.T) {
 					n: name
 				}
 			}
+			qc3: queryCharacter {
+				... on Droid{
+					__typename
+					primaryFunction
+				}
+				... on Employee {
+					__typename
+					ename
+				}
+				... on Human {
+					__typename
+					name
+				}
+			}
 			qcRep1: queryCharacter {
 				name
 				... on Human {
@@ -316,6 +330,17 @@ func fragmentInQueryOnInterface(t *testing.T) {
 			{
 			}
 		],
+		"qc3":[
+			{
+				"__typename":"Human",
+				"ename":"Han_employee",
+				"name":"Han"
+			},
+			{
+				"__typename":"Droid",
+				"primaryFunction":"Robot"
+			}
+		],
 		"qcRep1": [
             {
 				"name": "Han",

graphql/resolve/query_test.yaml

@@ -1935,6 +1935,32 @@
       }
     }
 
+-
+  name: "queryCharacter with fragment on interface and type"
+  gqlquery: |
+    query {
+      queryCharacter {
+        id
+        name
+        ... on Employee {
+            ename
+        }
+        ... on Human {
+            female
+        }
+      }
+    }
+  dgquery: |-
+    query {
+      queryCharacter(func: type(Character)) {
+        dgraph.type
+        id : uid
+        name : Character.name
+        ename : Employee.ename
+        female : Human.female
+      }
+    }
+
 -
   name: "Filter with id uses uid func at root."
   gqlquery: |

graphql/schema/request.go

@@ -275,28 +275,20 @@ func recursivelyExpandFragmentSelections(field *ast.Field, op *operation) {
 	satisfies := []string{typeName, ""}
 	var additionalTypes map[string]bool
 	switch typeKind {
-	case ast.Interface:
-		// expand fragments on types which implement this interface
+	case ast.Interface, ast.Union:
+		// expand fragments on types which implement this interface (for interface case)
+		// expand fragments on member types of this union (for Union case)
 		additionalTypes = getTypeNamesAsMap(op.inSchema.schema.PossibleTypes[typeName])
-		// if there is any fragment in the selection set of this field, need to store a mapping from
-		// fields in that fragment to the fragment's type condition, to be used later in completion.
-		for _, f := range field.SelectionSet {
-			addSelectionToInterfaceImplFragFields(typeName, f, additionalTypes, op)
-		}
-	case ast.Union:
-		// expand fragments on member types of this union
-		additionalTypes = getTypeNamesAsMap(op.inSchema.schema.PossibleTypes[typeName])
-		// also, expand fragments on interfaces which are implemented by the member types of this
-		// union
+		// also, expand fragments on interfaces which are implemented by the member types of this union
+		// And also on additional interfaces which also implement the same type
 		var interfaceFragsToExpand []*ast.Definition
-		for memberType := range additionalTypes {
+		for Type := range additionalTypes {
 			interfaceFragsToExpand = append(interfaceFragsToExpand,
-				op.inSchema.schema.Implements[memberType]...)
+				op.inSchema.schema.Implements[Type]...)
 		}
 		additionalInterfaces := getTypeNamesAsMap(interfaceFragsToExpand)
-		// for fragments in the selection set of this union field, need to store a mapping from
-		// fields in that fragment to the fragment's type condition, for each of the additional
-		// interfaces, to be used later in completion.
+		// if there is any fragment in the selection set of this field, need to store a mapping from
+		// fields in that fragment to the fragment's type condition, to be used later in completion.
 		for interfaceName := range additionalInterfaces {
 			additionalTypes[interfaceName] = true
 			for _, f := range field.SelectionSet {