Fix preload many2many problem when no search results, #688

join_table_handler.go

@@ -134,7 +134,6 @@ func (s JoinTableHandler) JoinWith(handler JoinTableHandlerInterface, db *DB, so
 	scope := db.NewScope(source)
 	modelType := scope.GetModelStruct().ModelType
 	var joinConditions []string
-	var queryConditions []string
 	var values []interface{}
 	if s.Source.ModelType == modelType {
 		destinationTableName := db.NewScope(reflect.New(s.Destination.ModelType).Interface()).QuotedTableName()
@@ -152,12 +151,15 @@ func (s JoinTableHandler) JoinWith(handler JoinTableHandlerInterface, db *DB, so
 
 		foreignFieldValues := scope.getColumnAsArray(foreignFieldNames)
 
-		condString := fmt.Sprintf("%v in (%v)", toQueryCondition(scope, foreignDBNames), toQueryMarks(foreignFieldValues))
+		var condString string
+		if len(foreignFieldValues) > 0 {
+			condString = fmt.Sprintf("%v IN (%v)", toQueryCondition(scope, foreignDBNames), toQueryMarks(foreignFieldValues))
 
-		keys := scope.getColumnAsArray(foreignFieldNames)
-		values = append(values, toQueryValues(keys))
-
-		queryConditions = append(queryConditions, condString)
+			keys := scope.getColumnAsArray(foreignFieldNames)
+			values = append(values, toQueryValues(keys))
+		} else {
+			condString = fmt.Sprintf("1 <> 1")
+		}
 
 		return db.Joins(fmt.Sprintf("INNER JOIN %v ON %v", quotedTable, strings.Join(joinConditions, " AND "))).
 			Where(condString, toQueryValues(foreignFieldValues)...)

preload.go

@@ -63,7 +63,7 @@ func Preload(scope *Scope) {
 				case "belongs_to":
 					currentScope.handleBelongsToPreload(field, conditions)
 				case "many_to_many":
-					currentScope.handleHasManyToManyPreload(field, conditions)
+					currentScope.handleManyToManyPreload(field, conditions)
 				default:
 					currentScope.Err(errors.New("not supported relation"))
 				}
@@ -191,9 +191,8 @@ func (scope *Scope) handleBelongsToPreload(field *Field, conditions []interface{
 	}
 }
 
-func (scope *Scope) handleHasManyToManyPreload(field *Field, conditions []interface{}) {
+func (scope *Scope) handleManyToManyPreload(field *Field, conditions []interface{}) {
 	relation := field.Relationship
-
 	joinTableHandler := relation.JoinTableHandler
 	destType := field.StructField.Struct.Type.Elem()
 	var isPtr bool
@@ -211,6 +210,7 @@ func (scope *Scope) handleHasManyToManyPreload(field *Field, conditions []interf
 
 	db := scope.NewDB().Table(scope.New(reflect.New(destType).Interface()).TableName()).Select("*")
 	preloadJoinDB := joinTableHandler.JoinWith(joinTableHandler, db, scope.Value)
+
 	if len(conditions) > 0 {
 		preloadJoinDB = preloadJoinDB.Where(conditions[0], conditions[1:]...)
 	}

preload_test.go

@@ -689,6 +689,10 @@ func TestManyToManyPreloadWithMultiPrimaryKeys(t *testing.T) {
 	if !reflect.DeepEqual(got4, []Level2{got, got2}) {
 		t.Errorf("got %s; want %s", toJSONString(got4), toJSONString([]Level2{got, got2}))
 	}
+
+	if err := DB.Preload("Level1s").Find(&got4, "value IN (?)", []string{"non-existing"}).Error; err != nil {
+		panic(err)
+	}
 }
 
 func TestManyToManyPreloadForPointer(t *testing.T) {