fix(GraphQL): Fix case where Dgraph type was not generated for GraphQ…

…L interface (#5738)

* Generate type in Dgraph for interface using other interface

* Add test

graphql/schema/dgraph_schemagen_test.yml

@@ -243,6 +243,49 @@ schemas:
       }
       C.dob: dateTime .
 
+  -
+    name: "interface using other interface generate type in dgraph"
+    input: |
+      interface A {
+        id: ID!
+        data: [D]
+      }
+      type C implements A {
+          lname: String
+      }
+      interface B {
+          name: String! @id
+          fname: String!
+      }
+      type D implements B {
+        link: A 
+        correct: Boolean!
+      }
+    output: |
+      type A {
+        A.data
+      }
+      A.data: [uid] .
+      type C {
+        A.data
+        C.lname
+      }
+      C.lname: string .
+      type B {
+        B.name
+        B.fname
+      }
+      B.name: string @index(hash) @upsert .
+      B.fname: string .
+      type D {
+        B.name
+        B.fname
+        D.link
+        D.correct
+      }
+      D.link: uid .
+      D.correct: bool .
+
   -
     name: "Schema with @dgraph directive."
     input: |

graphql/schema/schemagen.go

@@ -416,7 +416,7 @@ func genDgSchema(gqlSch *ast.Schema, definitions []string) string {
 
 				var typStr string
 				switch gqlSch.Types[f.Type.Name()].Kind {
-				case ast.Object:
+				case ast.Object,ast.Interface:
 					typStr = fmt.Sprintf("%suid%s", prefix, suffix)
 
 					if parentInt == nil {