gorm 一对多关系以及预加载的用法-阿里云开发者社区

gorm 一对多关系以及预加载的用法

2024-01-15 138

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简介： gorm 一对多关系以及预加载的用法

一对多关系的介绍

这里女神表里面有多个舔狗，就是一对多has many关系

并且舔狗表里面包含Info信息表，是has one关系

type GirlGOD struct {
  gorm.Model
  Name string
  Dog  []Dog
}
type Dog struct {
  gorm.Model
  Name      string
  GirlGodID uint
  Info      Info
}
type Info struct {
  gorm.Model
  Age   int
  Money int
  DogID uint
}
func main() {
  db, _ := gorm.Open(mysql.New(mysql.Config{DSN: "root:123456@tcp(127.0.0.1:3306)/gormDB?charset=utf8mb4&parseTime=True&loc=Local"}), &gorm.Config{})
  db.AutoMigrate(&GirlGOD{}, &Dog{}, &Info{})
  info1 := Info{
    Age:   1,
    Money: 1,
  }
  info2 := Info{
    Age:   2,
    Money: 2,
  }
  dog1 := Dog{
    Name: "dog1",
    Info: info1,
  }
  dog2 := Dog{
    Name: "dog2",
    Info: info2,
  }
  girl1 := GirlGOD{
    Name: "girl1",
    Dogs:  []Dog{dog1},
  }
  girl2 := GirlGOD{
    Name: "girl2",
    Dogs:  []Dog{dog2},
  }
  db.Debug().Create(&girl1)
  db.Debug().Create(&girl2)
}

预加载

Preload预加载

Preload 在一个单独查询中加载关联数据。

不使用预加载

查不出关联的舔狗的信息

func main() {
  db, _ := gorm.Open(mysql.New(mysql.Config{DSN: "root:123456@tcp(127.0.0.1:3306)/gormDB?charset=utf8mb4&parseTime=True&loc=Local"}), &gorm.Config{})
  db.AutoMigrate(&GirlGOD{}, &Dog{}, &Info{})
  var girls []GirlGOD
  db.Debug().Find(&girls)
  fmt.Println(girls)
  for _, v := range girls {
    for i := range v.Dogs {
      fmt.Println(v.Name, v.Dogs[i].Name, v.Dogs[i].Info.Money)
    }
  }
}

2022/05/15 22:53:29 C:/Users/68725/Desktop/leetcode/main.go:32
[42.024ms] [rows:2] SELECT * FROM `girl_gods` WHERE `girl_gods`.`deleted_at` IS NULL
[{{1 2022-05-15 22:43:14.714 +0800 CST 2022-05-15 22:43:14.714 +0800 CST {0001-01-01 00:00:00 +0000 UTC false}} girl1 []} {{2 2022-05-15 22:43:14.756 +0800 CST 2022-05-15 22:43:14.756 +0800 CST {0001-01-01 00:00:00 +0000 UTC false}} girl2 []}]

使用预加载

查出与girlgod关联的dog表的信息，但是与dog表关联的info表信息没有

func main() {
  db, _ := gorm.Open(mysql.New(mysql.Config{DSN: "root:123456@tcp(127.0.0.1:3306)/gormDB?charset=utf8mb4&parseTime=True&loc=Local"}), &gorm.Config{})
  db.AutoMigrate(&GirlGOD{}, &Dog{}, &Info{})
  var girls []GirlGOD
  db.Debug().Preload("Dogs").Find(&girls)
  fmt.Println(girls)
  for _, v := range girls {
    for i := range v.Dogs {
      fmt.Println(v.Name, v.Dogs[i].Name, v.Dogs[i].Info.Money)
    }
  }
}

2022/05/15 22:54:22 C:/Users/68725/Desktop/leetcode/main.go:32
[0.651ms] [rows:2] SELECT * FROM `dogs` WHERE `dogs`.`girl_god_id` IN (1,2) AND `dogs`.`deleted_at` IS NULL
2022/05/15 22:54:22 C:/Users/68725/Desktop/leetcode/main.go:32
[49.459ms] [rows:2] SELECT * FROM `girl_gods` WHERE `girl_gods`.`deleted_at` IS NULL
[{{1 2022-05-15 22:43:14.714 +0800 CST 2022-05-15 22:43:14.714 +0800 CST {0001-01-01 00:00:00 +0000 UTC false}} girl1 [{{1 2022-05-15 22:43:14.752 +0800 CST 2022-05-15 22:43:14.752 +0800 CST {0001-01-01 00:00:00 +0000 UTC false}} dog1 1 {{0 0001-01-01 00:00:00 +0000 UTC 0001-01-01 00:00:00 +0000 UTC {0001-01-01 00:00:00 +0000 UTC false}} 0 0 0}}]} {{2 2022-05-15 22:43:14.756 +0800 CST 2022-05-15 22:43:14.756 +0800 CST {0001-01-01 00:00:00 +0000 UTC false}} girl2 [{{2 2022-05-15 22:43:14.757 +0800 CST 2022-05-15 22:43:14.757 +0800 CST {0001-01-01 00:00:00 +0000 UTC false}} dog2 2 {{0 0001-01-01 00:00:00 +0000 UTC 0001-01-01 00:00:00 +0000 UTC {0001-01-01 00:00:00 +0000 UTC false}} 0 0 0}}]}]
girl1 dog1 0
girl2 dog2 0

func main() {
  db, _ := gorm.Open(mysql.New(mysql.Config{DSN: "root:123456@tcp(127.0.0.1:3306)/gormDB?charset=utf8mb4&parseTime=True&loc=Local"}), &gorm.Config{})
  db.AutoMigrate(&GirlGOD{}, &Dog{}, &Info{})
  var girls []GirlGOD
  db.Debug().Preload("Dogs.Info").Preload("Dogs").Find(&girls)
  fmt.Println(girls)
  for _, v := range girls {
    for i := range v.Dogs {
      fmt.Println(v.Name, v.Dogs[i].Name, v.Dogs[i].Info.Money)
    }
  }
}

使用链式预加载

将与girlgod关联的dog表的信息，dog表与info表关联的信息都查出来

2022/05/15 22:55:26 C:/Users/68725/Desktop/leetcode/main.go:32
[0.000ms] [rows:2] SELECT * FROM `infos` WHERE `infos`.`dog_id` IN (1,2) AND `infos`.`deleted_at` IS NULL
2022/05/15 22:55:26 C:/Users/68725/Desktop/leetcode/main.go:32
[1.531ms] [rows:2] SELECT * FROM `dogs` WHERE `dogs`.`girl_god_id` IN (1,2) AND `dogs`.`deleted_at` IS NULL
2022/05/15 22:55:26 C:/Users/68725/Desktop/leetcode/main.go:32
[44.470ms] [rows:2] SELECT * FROM `girl_gods` WHERE `girl_gods`.`deleted_at` IS NULL
[{{1 2022-05-15 22:43:14.714 +0800 CST 2022-05-15 22:43:14.714 +0800 CST {0001-01-01 00:00:00 +0000 UTC false}} girl1 [{{1 2022-05-15 22:43:14.752 +0800 CST 2022-05-15 22:43:14.752 +0800 CST {0001-01-01 00:00:00 +0000 UTC false}} dog1 1 {{1 2022-05-15 22:43:14.753 +0800 CST 2022-05-15 22:43:14.753 +0800 CST {0001-01-01 00:00:00 +0000 UTC false}} 1 1 1}}]} {{2 2022-05-15 22:43:14.756 +0800 CST 2022-05-15 22:43:14.756 +0800 CST {0001-01-01 00:00:00 +0000 UTC false}} girl2 [{{2 2022-05-15 22:43:14.757 +0800 CST 2022-05-15 22:43:14.757 +0800 CST {0001-01-01 00:00:00 +0000 UTC false}} dog2 2 {{2 2022-05-15 22:43:14.757 +0800 CST 2022-05-15 22:43:14.757 +0800 CST {0001-01-01 00:00:00 +0000 UTC false}} 2 2 2}}]}]
girl1 dog1 1
girl2 dog2 2

条件预加载

func main() {
  db, _ := gorm.Open(mysql.New(mysql.Config{DSN: "root:123456@tcp(127.0.0.1:3306)/gormDB?charset=utf8mb4&parseTime=True&loc=Local"}), &gorm.Config{})
  db.AutoMigrate(&GirlGOD{}, &Dog{}, &Info{})
  var girls []GirlGOD
  db.Debug().Preload("Dogs.Info", "money>0").Preload("Dogs", "name=?", "dog2").Find(&girls)
  fmt.Println(girls)
  for _, v := range girls {
    for i := range v.Dogs {
      fmt.Println(v.Name, v.Dogs[i].Name, v.Dogs[i].Info.Money)
    }
  }
}

2022/05/15 22:56:47 C:/Users/68725/Desktop/leetcode/main.go:32
[1.509ms] [rows:1] SELECT * FROM `infos` WHERE `infos`.`dog_id` = 2 AND money>0 AND `infos`.`deleted_at` IS NULL
2022/05/15 22:56:47 C:/Users/68725/Desktop/leetcode/main.go:32
[1.509ms] [rows:1] SELECT * FROM `dogs` WHERE `dogs`.`girl_god_id` IN (1,2) AND name='dog2' AND `dogs`.`deleted_at` IS NULL
2022/05/15 22:56:47 C:/Users/68725/Desktop/leetcode/main.go:32
[42.171ms] [rows:2] SELECT * FROM `girl_gods` WHERE `girl_gods`.`deleted_at` IS NULL
[{{1 2022-05-15 22:43:14.714 +0800 CST 2022-05-15 22:43:14.714 +0800 CST {0001-01-01 00:00:00 +0000 UTC false}} girl1 []} {{2 2022-05-15 22:43:14.756 +0800 CST 2022-05-15 22:43:14.756 +0800 CST {0001-01-01 00:00:00 +0000 UTC false}} girl2 [{{2 2022-05-15 22:43:14.757 +0800 CST 2022-05-15 22:43:14.757 +0800 CST {0001-01-01 00:00:00 +0000 UTC false}} dog2 2 {{2 2022-05-15 22:43:14.757 +0800 CST 2022-05-15 22:43:14.757 +0800 CST {0001-01-01 00:00:00 +0000 UTC false}} 2 2 2}}]}]
girl2 dog2 2

Joins 预加载

Join Preload 会使用 inner join 加载关联数据

注意 Join Preload 适用于一对一的关系，例如： has one, belongs to

func main() {
  db, _ := gorm.Open(mysql.New(mysql.Config{DSN: "root:123456@tcp(127.0.0.1:3306)/gormDB?charset=utf8mb4&parseTime=True&loc=Local"}), &gorm.Config{})
  db.AutoMigrate(&GirlGOD{}, &Dog{}, &Info{})
  var girls []GirlGOD
  db.Debug().Preload("Dogs", func(db *gorm.DB) *gorm.DB {
    return db.Joins("Info").Where("money>1")
  }).Find(&girls)
  fmt.Println(girls)
}

SELECT `dogs`.`id`,
       `dogs`.`created_at`,
       `dogs`.`updated_at`,
       `dogs`.`deleted_at`,
       `dogs`.`name`,
       `dogs`.`girl_god_id`,
       `Info`.`id`         AS `Info__id`,
       `Info`.`created_at` AS `Info__created_at`,
       `Info`.`updated_at` AS `Info__updated_at`,
       `Info`.`deleted_at` AS `Info__deleted_at`,
       `Info`.`age`        AS `Info__age`,
       `Info`.`money`      AS `Info__money`,
       `Info`.`dog_id`     AS `Info__dog_id`
FROM `dogs`
         LEFT JOIN `infos` `Info` ON `dogs`.`id` = `Info`.`dog_id` AND `Info`.`deleted_at` IS NULL
WHERE money > 1
  AND `dogs`.`girl_god_id` IN (1, 2)
  AND `dogs`.`deleted_at` IS NULL

gorm 一对多关系以及预加载的用法

一对多关系的介绍

预加载

Preload预加载

不使用预加载

使用预加载

使用链式预加载

条件预加载

Joins 预加载

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gorm 一对多关系 以及预加载的用法

一对多关系的介绍

预加载

Preload预加载

不使用预加载

使用预加载

使用链式预加载

条件预加载

Joins 预加载

热门文章

最新文章

相关电子书

相关实验场景

gorm 一对多关系以及预加载的用法