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。
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 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')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)外键添加
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`)
