many-to-many relationship
Many-to-many relationship, need to use the third table to store the relationship between the two tables
For many-to-many, the many2many tag must be added. article_tags is used to specify the third table,
package main
import (
"gorm.io/driver/mysql"
"gorm.io/gorm"
)
type Tag struct {
ID uint
Name string
Articles []Article `gorm:"many2many:articles_tags;"`
}
type Article struct {
ID uint
Title string
Tags []Tag `gorm:"many2many:articles_tags;"`
}
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.AutoMigrate(&Article{}, &Tag{})
db.Create(&Article{
Title: "python基础",
Tags: []Tag{
{Name: "python"},
{Name: "后端"},
},
})
}
mysql> select * from articles;
+----+--------------+
| id | title |
+----+--------------+
| 2 | python?虹? |
+----+--------------+
mysql> select * from tags;
+----+--------+
| id | name |
+----+--------+
| 1 | python |
| 2 | ?.. |
+----+--------+
mysql> select * from articles_tags;
+--------+------------+
| tag_id | article_id |
+--------+------------+
| 1 | 2 |
| 2 | 2 |
+--------+------------+An article and two tags are created, and their dependencies are also created. The third table will create itself.
If you want to associate an existing article, you have to check it first.
var tags []Tag
db.Find(&tags, "name in ?", []string{"python"})
db.AutoMigrate(&Article{}, &Tag{})
db.Create(&Article{
Title: "golang",
Tags: tags,
})
mysql> select * from articles_tags;
+--------+------------+
| tag_id | article_id |
+--------+------------+
| 1 | 2 |
| 2 | 2 |
| 1 | 4 |
+--------+------------+
mysql> select * from tags;
+----+--------+
| id | name |
+----+--------+
| 1 | python |
| 2 | ?.. |
+----+--------+
mysql> select * from articles;
+----+--------------+
| id | title |
+----+--------------+
| 2 | python?虹? |
| 3 | golang |
| 4 | golang |
+----+--------------+
