add CondIf interface (#53)

* add CondIf interface * fix comment

Author: lunny

cond_if.go

@@ -0,0 +1,46 @@
+// Copyright 2019 The Xorm Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package builder
+
+type condIf struct {
+condition bool
+condTrue Cond
+condFalse Cond
+}
+
+var _ Cond = condIf{}
+
+// If returns Cond via condition
+func If(condition bool, condTrue Cond, condFalse ...Cond) Cond {
+var c = condIf{
+condition: condition,
+condTrue: condTrue,
+}
+if len(condFalse) > 0 {
+c.condFalse = condFalse[0]
+}
+return c
+}
+
+func (condIf condIf) WriteTo(w Writer) error {
+if condIf.condition {
+return condIf.condTrue.WriteTo(w)
+} else if condIf.condFalse != nil {
+return condIf.condFalse.WriteTo(w)
+}
+return nil
+}
+
+func (condIf condIf) And(conds ...Cond) Cond {
+return And(condIf, And(conds...))
+}
+
+func (condIf condIf) Or(conds ...Cond) Cond {
+return Or(condIf, Or(conds...))
+}
+
+func (condIf condIf) IsValid() bool {
+return condIf.condTrue != nil
+}

cond_if_test.go

@@ -0,0 +1,28 @@
+// Copyright 2019 The Xorm Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package builder
+
+import (
+"testing"
+
+"github.com/stretchr/testify/assert"
+)
+
+func TestCond_If(t *testing.T) {
+var cond = If(1 > 0, Eq{"a": 1}, Eq{"b": 1})
+sql, err := ToBoundSQL(cond)
+assert.NoError(t, err)
+assert.EqualValues(t, "a=1", sql)
+
+cond = If(1 < 0, Eq{"a": 1}, Eq{"b": 1})
+sql, err = ToBoundSQL(cond)
+assert.NoError(t, err)
+assert.EqualValues(t, "b=1", sql)
+
+cond = If(1 > 0, cond, Eq{"c": 1})
+sql, err = ToBoundSQL(cond)
+assert.NoError(t, err)
+assert.EqualValues(t, "b=1", sql)
+}