Golang gorm manytomany 多对多 更新、删除、替换

Golang gorm manytomany 多对多 更新、删除、替换_第1张图片

 

 

 

Delete 移除 只删除中间表的数据   删除原有的


	var a Article1
	db.Preload("Tag1s").Take(&a, 1)
	fmt.Printf("%v", a)
{1 k8s [{1 cloud []} {2 linux []}]}

mysql> select * from article1;
+----+--------+
| id | title  |
+----+--------+
|  1 | k8s    |
|  2 | golang |
+----+--------+

mysql> select * from tag1;
+----+-------+
| id | name  |
+----+-------+
|  1 | cloud |
|  2 | linux |
+----+-------+

mysql> select * from article_tags;
+-------------+---------+
| article1_id | tag1_id |
+-------------+---------+
|           1 |       1 |
|           1 |       2 |
|           2 |       2 |
+-------------+---------+

(1)model 先拿到这张表,

(2)Association然后去连接tags第三张表

(3)之后就是最关键的要去执行什么操作,这里是delete,删除谁呢?删除的就是article关联的tag。

	var a Article1
	db.Preload("Tag1s").Take(&a, 1)
	db.Model(&a).Association("Tag1s").Delete(a.Tag1s)
	fmt.Printf("%v", a)

{1 k8s []}


mysql> select * from tag1;
+----+-------+
| id | name  |
+----+-------+
|  1 | cloud |
|  2 | linux |
+----+-------+

mysql> select * from article1;
+----+--------+
| id | title  |
+----+--------+
|  1 | k8s    |
|  2 | golang |
+----+--------+

mysql> select * from article_tags;
+-------------+---------+
| article1_id | tag1_id |
+-------------+---------+
|           2 |       2 |
+-------------+---------+

 

 

添加 和上面一样使用Append


	var t []Tag1
	db.Find(&t)

	var a Article1
	db.Preload("Tag1s").Take(&a, 1)
	db.Model(&a).Association("Tag1s").Append(&t)
	fmt.Printf("%v", a)

{1 k8s [{1 cloud []} {2 linux []}]}


mysql> select * from article1;
+----+--------+
| id | title  |
+----+--------+
|  1 | k8s    |
|  2 | golang |
+----+--------+

mysql> select * from tag1;
+----+-------+
| id | name  |
+----+-------+
|  1 | cloud |
|  2 | linux |
+----+-------+

mysql> select * from article_tags;
+-------------+---------+
| article1_id | tag1_id |
+-------------+---------+
|           1 |       1 |
|           1 |       2 |
|           2 |       2 |
+-------------+---------+

 

Replace  替换


	var t Tag1
	db.Take(&t, 1)

	var a Article1
	db.Preload("Tag1s").Take(&a, 2)
	db.Model(&a).Association("Tag1s").Replace(&t)
	fmt.Printf("%v", a)

{2 golang [{1 cloud []}]}

 

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