Bugfix: Set found to false to avoid deleting index edge when value do…

…esn't match. (#3843)

Return found as false to avoid deleting index corresponding to a uid when the value doesn't match. For scalar values, after fingerprinting found is always true as values get fingerprinted to math.MaxUint64. Hence we return found as false from this second check. Fixes #3803.

dgraph/cmd/alpha/run_test.go

@@ -1294,14 +1294,15 @@ func TestDeleteAllSP2(t *testing.T) {
 }
 
 func TestDeleteScalarValue(t *testing.T) {
-	var s = `name: string .`
+	var s = `name: string @index(exact) .`
 	require.NoError(t, schema.ParseBytes([]byte(""), 1))
 	require.NoError(t, alterSchemaWithRetry(s))
 
 	var m = `
 	{
 	  set {
-	    <0x12345> <name> "xxx" .
+		<0x12345> <name> "xxx" .
+		<0x12346> <name> "xxx" .
 	  }
 	}
 	`
@@ -1342,6 +1343,17 @@ func TestDeleteScalarValue(t *testing.T) {
 	require.NoError(t, err)
 	require.JSONEq(t, `{"data": {"me":[{"name":"xxx"}]}}`, output)
 
+	indexQuery := `
+	{
+		me(func: eq(name, "xxx")) {
+			name
+		}
+	}
+	`
+	output, err = runGraphqlQuery(indexQuery)
+	require.NoError(t, err)
+	require.JSONEq(t, `{"data": {"me":[{"name":"xxx"}, {"name":"xxx"}]}}`, output)
+
 	var d2 = `
 	{
       delete {
@@ -1356,6 +1368,11 @@ func TestDeleteScalarValue(t *testing.T) {
 	output, err = runGraphqlQuery(q)
 	require.NoError(t, err)
 	require.JSONEq(t, `{"data": {"me":[]}}`, output)
+
+	// Verify index was also updated this time and one of the triples got deleted.
+	output, err = runGraphqlQuery(indexQuery)
+	require.NoError(t, err)
+	require.JSONEq(t, `{"data": {"me":[{"name": "xxx"}]}}`, output)
 }
 
 func TestDeleteValueLang(t *testing.T) {

posting/index.go

@@ -329,9 +329,15 @@ func (txn *Txn) addMutationHelper(ctx context.Context, l *List, doUpdateIndex bo
 			return val, found, emptyCountParams, err
 		}
 
+		// This is a scalar value of non-list type and a delete edge mutation, so if the value
+		// given by the user doesn't match the value we have, we return found to be false, to avoid
+		// deleting the uid from index posting list.
+		// This second check is required because we fingerprint the scalar values as math.MaxUint64,
+		// so even though they might be different the check in the doUpdateIndex block above would
+		// return found to be true.
 		if pFound && !(bytes.Equal(currPost.Value, newPost.Value) &&
 			types.TypeID(currPost.ValType) == types.TypeID(newPost.ValType)) {
-			return val, found, emptyCountParams, err
+			return val, false, emptyCountParams, nil
 		}
 	}