add more test for join find (go-xorm#922)

Author: lunny

error.go

@@ -26,10 +26,18 @@ var (
 	ErrNotImplemented = errors.New("Not implemented")
 	// ErrConditionType condition type unsupported
 	ErrConditionType = errors.New("Unsupported condition type")
-	// ErrFieldIsNotExist columns does not exist
-	ErrFieldIsNotExist = errors.New("Field does not exist")
 )
 
+// ErrFieldIsNotExist columns does not exist
+type ErrFieldIsNotExist struct {
+	FieldName string
+	TableName string
+}
+
+func (e ErrFieldIsNotExist) Error() string {
+	return fmt.Sprintf("field %s is not valid on table %s", e.FieldName, e.TableName)
+}
+
 // ErrFieldIsNotValid is not valid
 type ErrFieldIsNotValid struct {
 	FieldName string

session.go

@@ -281,7 +281,7 @@ func (session *Session) doPrepare(db *core.DB, sqlStr string) (stmt *core.Stmt,
 func (session *Session) getField(dataStruct *reflect.Value, key string, table *core.Table, idx int) (*reflect.Value, error) {
 	var col *core.Column
 	if col = table.GetColumnIdx(key, idx); col == nil {
-		return nil, ErrFieldIsNotExist
+		return nil, ErrFieldIsNotExist{key, table.Name}
 	}
 
 	fieldValue, err := col.ValueOfV(dataStruct)

session_find_test.go

@@ -770,7 +770,7 @@ func TestFindCacheLimit(t *testing.T) {
 
 func TestFindJoin(t *testing.T) {
 	type SceneItem struct {
-		Type int
+		Type     int
 		DeviceId int64
 	}
 
@@ -786,4 +786,9 @@ func TestFindJoin(t *testing.T) {
 	err := testEngine.Join("LEFT OUTER", "device_user_privrels", "device_user_privrels.device_id=scene_item.device_id").
 		Where("scene_item.type=?", 3).Or("device_user_privrels.user_id=?", 339).Find(&scenes)
 	assert.NoError(t, err)
+
+	scenes = make([]SceneItem, 0)
+	err = testEngine.Join("LEFT OUTER", new(DeviceUserPrivrels), "device_user_privrels.device_id=scene_item.device_id").
+		Where("scene_item.type=?", 3).Or("device_user_privrels.user_id=?", 339).Find(&scenes)
+	assert.NoError(t, err)
 }