Merge pull request #2330 from xwjdsh/bugfix/return-empty-slice-many2many

Return empty slice for many2many if no asscociation was found

callback_query_preload.go

@@ -391,14 +391,20 @@ func (scope *Scope) handleManyToManyPreload(field *Field, conditions []interface
 		key := toString(getValueFromFields(indirectScopeValue, foreignFieldNames))
 		fieldsSourceMap[key] = append(fieldsSourceMap[key], indirectScopeValue.FieldByName(field.Name))
 	}
-	for source, link := range linkHash {
-		for i, field := range fieldsSourceMap[source] {
+
+	for source, fields := range fieldsSourceMap {
+		for _, f := range fields {
 			//If not 0 this means Value is a pointer and we already added preloaded models to it
-			if fieldsSourceMap[source][i].Len() != 0 {
+			if f.Len() != 0 {
 				continue
 			}
-			field.Set(reflect.Append(fieldsSourceMap[source][i], link...))
-		}
 
+			v := reflect.MakeSlice(f.Type(), 0, 0)
+			if len(linkHash[source]) > 0 {
+				v = reflect.Append(f, linkHash[source]...)
+			}
+
+			f.Set(v)
+		}
 	}
 }

preload_test.go

@@ -771,6 +771,7 @@ func TestNestedPreload11(t *testing.T) {
 	levelB3 := &LevelB3{
 		Value:     "bar",
 		LevelB1ID: sql.NullInt64{Valid: true, Int64: int64(levelB1.ID)},
+		LevelB2s:  []*LevelB2{},
 	}
 	if err := DB.Create(levelB3).Error; err != nil {
 		t.Error(err)