• 判断某个记录是否存在可以使用Exist, 相比Get，Exist性能更好。

  package main
  
  import (
    "fmt"
    _ "github.com/go-sql-driver/mysql"
    "github.com/go-xorm/xorm"
    "log"
    "time"
  )
  
  var engine *xorm.Engine
  
  type User struct {
    Name      string    `xorm:"varchar(25) 'name'"`
    Id        int       `xorm:"pk 'id' autoincr"`
    CreatedAt time.Time `xorm:"created"`
  }
  
  func main() {
    var err error
    engine, err = xorm.NewEngine("mysql", "root:123456@/test")
    if err != nil {
        log.Fatal(err)
        return
    }
  
    err = engine.CreateTables(User{})
    if err != nil {
        log.Fatal(err)
        return
    }
  
    u := make([]User, 5)
    u[0].Name = "abcd"
    u[1].Name = "acbd"
    u[2].Name = "dbac"
    u[3].Name = "cbda"
    u[4].Name = "bdca"
  
    _, err = engine.Insert(u)
    if err != nil {
        log.Fatal(err)
        return
    }
    /*
        has, err := testEngine.Exist(new(RecordExist))
        // SELECT * FROM record_exist LIMIT 1、
    */
    uu := new(User)
    uu.Name = "abcd"
    has, err := engine.Exist(uu)
    if err != nil {
        log.Fatal(err)
        return
    }
    if has {
        fmt.Println("uu ",uu.Name, uu.Id, uu.CreatedAt)
    }
  
    /*
        has, err = testEngine.Exist(&RecordExist{
            Name: "test1",
        })
        // SELECT * FROM record_exist WHERE name = ? LIMIT 1
    */
    uu0 := &User{Name: "abcd"}
    has, err = engine.Exist(uu0)
    if err != nil {
        log.Fatal(err)
        return
    }
    if has {
        fmt.Println("uu0 ",uu0.Name, uu0.Id, uu0.CreatedAt)
    }
  
    /*
        has, err = testEngine.Where("name = ?", "test1").Exist(&RecordExist{})
        // SELECT * FROM record_exist WHERE name = ? LIMIT 1
    */
    uu1 := &User{Name: "abcd"}
    has, err = engine.Where("id =?", 1).Exist(uu1)
    if err != nil {
        log.Fatal(err)
        return
    }
    if has {
        fmt.Println("uu1 ",uu1.Name, uu1.Id, uu1.CreatedAt)
    }
  
    /*
        has, err = testEngine.SQL("select * from record_exist where name = ?", "test1").Exist()
        // select * from record_exist where name = ?
  
    */
  
    uu2 := new(User)
    has, err = engine.SQL("select * from user where id =?", 2).Exist(uu2)
    if err != nil {
        log.Fatal(err)
        return
    }
    if has {
        fmt.Println("uu2 ",uu2.Name, uu2.Id, uu2.CreatedAt)
    }
  
    /*
        has, err = testEngine.Table("record_exist").Exist()
        // SELECT * FROM record_exist LIMIT 1
    */
  
    uu3 := new(User)
    has, err = engine.Table(User{}).Exist(uu3)
    if err != nil {
        log.Fatal(err)
        return
    }
    if has {
        fmt.Println("uu3 ",uu3.Name, uu3.Id, uu3.CreatedAt)
    }
  
    /*
        has, err = testEngine.Table("record_exist").Where("name = ?", "test1").Exist()
        // SELECT * FROM record_exist WHERE name = ? LIMIT 1
    */
    uu4 := new(User)
    has, err = engine.Table(User{}).Where("name =?", "abcd").Exist(uu4)
    if err != nil {
        log.Fatal(err)
        return
    }
    if has {
        fmt.Println("uu4 ",uu4.Name, uu4.Id, uu4.CreatedAt)
    }
  
  }
  
  /*
  输出：
  uu  abcd 0 0001-01-01 00:00:00 +0000 UTC
  uu0  abcd 0 0001-01-01 00:00:00 +0000 UTC
  uu1  abcd 0 0001-01-01 00:00:00 +0000 UTC
  uu2   0 0001-01-01 00:00:00 +0000 UTC
  uu3   0 0001-01-01 00:00:00 +0000 UTC
  uu4   0 0001-01-01 00:00:00 +0000 UTC
  可以发现体存在的情况下，Exist方法不会将查到的实体赋值给参数
  */
  

• 与Get的区别

  • Get与Exist方法返回值都为bool和error，如果查询到实体存在，则Get方法会将查到的实体赋值给参数

    user := &User{Id:1}
    has,err := testEngine.Get(user) 
    // 执行结束后，user会被赋值为数据库中Id为1的实体
    has,err = testEn