improve update error when no conent to be updated (#648)

session_update.go

@@ -330,6 +330,10 @@ func (session *Session) Update(bean interface{}, condiBean ...interface{}) (int6
 		}
 	}
 
+	if len(colNames) <= 0 {
+		return 0, errors.New("No content found to be updated")
+	}
+
 	sqlStr = fmt.Sprintf("UPDATE %v%v SET %v %v",
 		top,
 		session.Engine.Quote(session.Statement.TableName()),

session_update_test.go

@@ -1093,3 +1093,23 @@ func TestBool(t *testing.T) {
 		}
 	}
 }
+
+func TestNoUpdate(t *testing.T) {
+	assert.NoError(t, prepareEngine())
+
+	type NoUpdate struct {
+		Id      int64
+		Content string
+	}
+
+	assertSync(t, new(NoUpdate))
+
+	_, err := testEngine.Insert(&NoUpdate{
+		Content: "test",
+	})
+	assert.NoError(t, err)
+
+	_, err = testEngine.Id(1).Update(&NoUpdate{})
+	assert.Error(t, err)
+	assert.EqualValues(t, "No content found to be updated", err.Error())
+}