Return errors alongside result instead of just an error

queryer.go

@@ -93,16 +93,12 @@ type QueryerFunc func(*QueryInput) (interface{}, error)
 // Query invokes the provided function and writes the response to the receiver
 func (q QueryerFunc) Query(ctx context.Context, input *QueryInput, receiver interface{}) error {
 	// invoke the handler
-	response, err := q(input)
-	if err != nil {
-		return err
+	response, responseErr := q(input)
+	if response != nil {
+		// assume the mock is writing the same kind as the receiver
+		reflect.ValueOf(receiver).Elem().Set(reflect.ValueOf(response))
 	}
-
-	// assume the mock is writing the same kind as the receiver
-	reflect.ValueOf(receiver).Elem().Set(reflect.ValueOf(response))
-
-	// no errors
-	return nil
+	return responseErr // support partial success: always return the queryer error after setting the return data
 }
 
 type NetworkQueryer struct {

queryerMultiOp.go

@@ -73,11 +73,6 @@ func (q *MultiOpQueryer) Query(ctx context.Context, input *QueryInput, receiver
 	}
 
 	// format the result as needed
-	err = q.queryer.ExtractErrors(unmarshaled)
-	if err != nil {
-		return err
-	}
-
 	// assign the result under the data key to the receiver
 	decoder, err := mapstructure.NewDecoder(&mapstructure.DecoderConfig{
 		TagName: "json",
@@ -86,9 +81,11 @@ func (q *MultiOpQueryer) Query(ctx context.Context, input *QueryInput, receiver
 	if err != nil {
 		return err
 	}
+	if err := decoder.Decode(unmarshaled["data"]); err != nil {
+		return err
+	}
 
-	// the only way for things to go wrong now happen while decoding
-	return decoder.Decode(unmarshaled["data"])
+	return q.queryer.ExtractErrors(unmarshaled)
 }
 
 func (q *MultiOpQueryer) loadQuery(ctx context.Context, keys dataloader.Keys) []*dataloader.Result {

queryerNetwork.go

@@ -3,8 +3,9 @@ package graphql
 import (
 	"context"
 	"encoding/json"
-	"github.com/mitchellh/mapstructure"
 	"net/http"
+
+	"github.com/mitchellh/mapstructure"
 )
 
 // SingleRequestQueryer sends the query to a url and returns the response
@@ -80,11 +81,6 @@ func (q *SingleRequestQueryer) Query(ctx context.Context, input *QueryInput, rec
 		return err
 	}
 
-	// otherwise we have to copy the response onto the receiver
-	if err = q.queryer.ExtractErrors(result); err != nil {
-		return err
-	}
-
 	// assign the result under the data key to the receiver
 	decoder, err := mapstructure.NewDecoder(&mapstructure.DecoderConfig{
 		TagName: "json",
@@ -93,7 +89,10 @@ func (q *SingleRequestQueryer) Query(ctx context.Context, input *QueryInput, rec
 	if err != nil {
 		return err
 	}
+	if err = decoder.Decode(result["data"]); err != nil {
+		return err
+	}
 
-	// the only way for things to go wrong now happen while decoding
-	return decoder.Decode(result["data"])
+	// finally extract errors, if any, and return them
+	return q.queryer.ExtractErrors(result) // TODO add unit tests!
 }

queryer_test.go

@@ -368,9 +368,10 @@ func TestQueryerWithMiddlewares(t *testing.T) {
 	for _, row := range queryerTable {
 		t.Run(row.name, func(t *testing.T) {
 			t.Run("Middleware Failures", func(t *testing.T) {
+				someErr := errors.New("This One")
 				queryer := row.queryer.WithMiddlewares([]NetworkMiddleware{
 					func(r *http.Request) error {
-						return errors.New("This One")
+						return someErr
 					},
 				})
 
@@ -381,13 +382,7 @@ func TestQueryerWithMiddlewares(t *testing.T) {
 
 				// fire the query
 				err := queryer.Query(context.Background(), input, &map[string]interface{}{})
-				if err == nil {
-					t.Error("Did not enounter an error when we should have")
-					return
-				}
-				if err.Error() != "This One" {
-					t.Errorf("Did not encountered expected error message: Expected 'This One', found %v", err.Error())
-				}
+				assert.ErrorIs(t, err, someErr)
 			})
 
 			t.Run("Middlware success", func(t *testing.T) {