Golang Gorm 一对多的添加

一对多的添加有两种情况：

一种是添加用户的时候同时创建文章
其次是创建文章关联已经存在的用户

添加用户的时候同时创建文章

package mainimport ("gorm.io/driver/mysql""gorm.io/gorm"
)// User 用户表 一个用户拥有多篇文章
type User struct {ID       int64Name     string    `gorm:"size:6"`Articles []Article //用户拥有的文章列表 has many
}type Article struct {ID     int64  `gorm:"size:4"`Title  string `gorm:"size:16"`UserID int64  //属于  belongs toUser   User   //属于  belongs to
}func (*User) TableName() string {return "user"
}func (*Article) TableName() string {return "article"
}func main() {dsn := "root:7PXjAkY!&nlR@tcp(192.168.11.128:3306)/test?charset=utf8mb4&parseTime=True&loc=Local"db, _ := gorm.Open(mysql.Open(dsn), &gorm.Config{})db.Debug().AutoMigrate(&User{}, &Article{})var u Usera1 := Article{Title: "redis",}u = User{Name: "yanzi",Articles: []Article{{Title: "golang",},{Title: "k8s",},a1,},}db.Debug().Create(&u)
}[8.981ms] [rows:3] INSERT INTO `article` (`title`,`user_id`) VALUES ('golang',2),('k8s',2),('redis',2) ON DUPLICATE KEY UPDATE `user_id`=VALUES(`user
_id`)
[14.812ms] [rows:1] INSERT INTO `user` (`name`) VALUES ('yanzi')

创建文章关联已经存在的用户

最后一种就是关联已有用户

	var articles []Articlearticles = []Article{{Title:  "cherry",UserID: 2,},{Title:  "marry",UserID: 2,},}db.Debug().Create(&articles)[11.754ms] [rows:2] INSERT INTO `article` (`title`,`user_id`) VALUES ('cherry',2),('marry',2)

创建用户文章并且关联

	db.Debug().Create(&Article{Title: "c",User: User{Name: "yanzi",},})

	var u Userdb.Debug().Take(&u, 2)db.Create(&Article{Title: "php",User:  u,})

model是声明映射关系的对象类型，通过这个对象类型，找到表名和字段。
Association 是关联某个一对多的字段
find是查找一对多关系 append是更新或者新增一对多关系

Association 关联的是字段，为字符串。后面的find和append是具体的结构体指针变量！！！

db.Model(&user).Association("CreditCard").Find(&user.CreditCard)db.Debug().Model(&u).Association("Articles").Append(&a)

外键添加现有文章关联已有用户

	var u Userdb.Debug().Take(&u, 3)var a Articledb.Debug().Take(&a, 7)u.Articles = []Article{a}db.Debug().Save(&u)[1.300ms] [rows:1] SELECT * FROM `user` WHERE `user`.`id` = 3 LIMIT 1[1.629ms] [rows:1] SELECT * FROM `article` WHERE `article`.`id` = 7 LIMIT 1[2.901ms] [rows:2] INSERT INTO `article` (`title`,`user_id`,`id`) VALUES ('marry',3,7) ON DUPLICATE KEY UPDATE `user_id`=VALUES(`user_id`)[6.363ms] [rows:0] UPDATE `user` SET `name`='test' WHERE `id` = 3[0.557ms] [rows:0] INSERT INTO `article` (`title`,`user_id`,`id`) VALUES ('marry',3,7) ON DUPLICATE KEY UPDATE `user_id`=VALUES(`user_id`)[3.713ms] [rows:0] INSERT INTO `user` (`name`,`id`) VALUES ('test',3) ON DUPLICATE KEY UPDATE `name`=VALUES(`name`)mysql> select * from user;
+----+-------+
| id | name  |
+----+-------+
|  1 | lucas |
|  2 | yanzi |
|  3 | test  |
+----+-------+
mysql> select * from article;
+----+--------+---------+
| id | title  | user_id |
+----+--------+---------+
|  1 | golang |       1 |
|  2 | k8s    |       1 |
|  3 | golang |       2 |
|  4 | k8s    |       2 |
|  5 | redis  |       2 |
|  6 | cherry |       2 |
|  7 | marry  |       3 |
+----+--------+---------+

	var u Userdb.Debug().Take(&u, 3)var a Articledb.Debug().Take(&a, 6)db.Debug().Model(&u).Association("Articles").Append(&a)[2.196ms] [rows:2] INSERT INTO `article` (`title`,`user_id`,`id`) VALUES ('cherry',3,6) ON DUPLICATE KEY UPDATE `user_id`=VALUES(`user_id`)

model是声明映射关系的对象类型，通过这个对象类型，找到表名和字段。

	var u Userdb.Debug().Take(&u, 3)var a Articledb.Debug().Take(&a, 5)db.Debug().Model(&u).Association("Articles").Append(&a)[1.409ms] [rows:1] SELECT * FROM `user` WHERE `user`.`id` = 3 LIMIT 1
[1.254ms] [rows:1] SELECT * FROM `article` WHERE `article`.`id` = 5 LIMIT 1
[2.285ms] [rows:2] INSERT INTO `article` (`title`,`user_id`,`id`) VALUES ('redis',3,5) ON DUPLICATE KEY UPDATE `user_id`=VALUES(`user_id`)