golang ：ORM之 QueryBuilder

使用ORM的時候我們可以採用QueryBuilder 去構造SQL
qb的接口

// QueryBuilder is the Query builder interface
type QueryBuilder interface {
	Select(fields ...string) QueryBuilder
	ForUpdate() QueryBuilder
	From(tables ...string) QueryBuilder
	InnerJoin(table string) QueryBuilder
	LeftJoin(table string) QueryBuilder
	RightJoin(table string) QueryBuilder
	On(cond string) QueryBuilder
	Where(cond string) QueryBuilder
	And(cond string) QueryBuilder
	Or(cond string) QueryBuilder
	In(vals ...string) QueryBuilder
	OrderBy(fields ...string) QueryBuilder
	Asc() QueryBuilder
	Desc() QueryBuilder
	Limit(limit int) QueryBuilder
	Offset(offset int) QueryBuilder
	GroupBy(fields ...string) QueryBuilder
	Having(cond string) QueryBuilder
	Update(tables ...string) QueryBuilder
	Set(kv ...string) QueryBuilder
	Delete(tables ...string) QueryBuilder
	InsertInto(table string, fields ...string) QueryBuilder
	Values(vals ...string) QueryBuilder
	Subquery(sub string, alias string) string
	String() string
}

通過上面的接口我們可以看到 QueryBuilder 返回值也是一個QueryBuilder ，所以我們可以像平時寫SQL構建自己的SQL解析語句

	orm.RegisterDataBase("default", "mysql", "root:123456@tcp(127.0.0.1:3306)/test?charset=utf8", 30)
	orm.RegisterModel(new(UserInfo))
	o := orm.NewOrm()

上面代碼 ，鏈接了數據庫，創建了RegisterModel ，創建了Orm對象
接着創建QueryBuilder

qb, _ := orm.NewQueryBuilder("mysql")

目前支持以下四種數據庫初始化

// NewQueryBuilder return the QueryBuilder
func NewQueryBuilder(driver string) (qb QueryBuilder, err error) {
	if driver == "mysql" {
		qb = new(MySQLQueryBuilder)
	} else if driver == "tidb" {
		qb = new(TiDBQueryBuilder)
	} else if driver == "postgres" {
		err = errors.New("postgres query builder is not supported yet")
	} else if driver == "sqlite" {
		err = errors.New("sqlite query builder is not supported yet")
	} else {
		err = errors.New("unknown driver for query builder")
	}
	return
}

構造sql語句

qb.Select("*").From("user_info")
sql := qb.String()

執行sql

o.Raw(sql).QueryRows(&user)