From cec55674cb343c1c7f3e96dd9c5fe7867a42f5b8 Mon Sep 17 00:00:00 2001
From: Anurag <anurag@dgraph.io>
Date: Wed, 30 Sep 2020 12:43:46 +0530
Subject: [PATCH] fix(GraphQL Query): Remove extra fields when querying
 interfaces (#6596)

---
 graphql/e2e/common/fragment.go | 41 ++++++++++++++++++++++++++++++++++
 graphql/resolve/resolver.go    |  9 ++++++++
 2 files changed, 50 insertions(+)

diff --git a/graphql/e2e/common/fragment.go b/graphql/e2e/common/fragment.go
index 5e54ecaa19a..f92e2086a6b 100644
--- a/graphql/e2e/common/fragment.go
+++ b/graphql/e2e/common/fragment.go
@@ -161,6 +161,27 @@ func fragmentInQueryOnInterface(t *testing.T) {
 					id
 				}
 			}
+			qcRep1: queryCharacter {
+				name
+				... on Human {
+					name
+					totalCredits
+				}
+				... on Droid {
+					name
+					primaryFunction
+				}
+			}
+			qcRep2: queryCharacter {
+				... on Human {
+					totalCredits
+				}
+				name
+				... on Droid {
+					primaryFunction
+					name
+				}
+			}
 			queryThing {
 				__typename
 				... on ThingOne {
@@ -269,6 +290,26 @@ func fragmentInQueryOnInterface(t *testing.T) {
 				"id": "%s"
 			}
 		],
+		"qcRep1": [
+            {
+				"name": "Han",
+                "totalCredits": 10
+            },
+            {
+                "name": "R2-D2",
+                "primaryFunction": "Robot"
+            }
+		],
+		"qcRep2": [
+            {
+                "totalCredits": 10,
+                "name": "Han"
+            },
+            {
+                "name": "R2-D2",
+                "primaryFunction": "Robot"
+            }
+		],
 		"queryThing":[
 			{
 				"__typename": "ThingOne",
diff --git a/graphql/resolve/resolver.go b/graphql/resolve/resolver.go
index b04c4bb6e1e..afbeed1a3e2 100644
--- a/graphql/resolve/resolver.go
+++ b/graphql/resolve/resolver.go
@@ -1268,6 +1268,10 @@ func completeObject(
 	var buf bytes.Buffer
 	comma := ""
 
+	// Below map keeps track of fields which have been seen as part of
+	// interface to avoid double entry in the resulting response
+	seenField := make(map[string]bool)
+
 	x.Check2(buf.WriteRune('{'))
 	dgraphTypes, ok := res["dgraph.type"].([]interface{})
 	for _, f := range fields {
@@ -1285,6 +1289,9 @@ func completeObject(
 		if len(dgraphTypes) > 0 {
 			includeField = f.IncludeInterfaceField(dgraphTypes)
 		}
+		if _, ok := seenField[f.ResponseName()]; ok {
+			includeField = false
+		}
 		if !includeField {
 			continue
 		}
@@ -1294,6 +1301,8 @@ func completeObject(
 		x.Check2(buf.WriteString(f.ResponseName()))
 		x.Check2(buf.WriteString(`": `))
 
+		seenField[f.ResponseName()] = true
+
 		val := res[f.DgraphAlias()]
 		if f.Name() == schema.Typename {
 			// From GraphQL spec: