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开发建设网站免费建站有哪些

news 2025/7/27 15:32:11

开发建设网站,免费建站有哪些,安徽疫情最新消息今天封城了,今日深圳宝安区最新消息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 …

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`)