Golang gorm manytomany many-to-many update, delete, replace

 

 

 

Delete removes only the data in the intermediate table and deletes the original

---

	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 first gets this table,

(2) Association then connects the third table of tags

(3) After that, the most critical thing is what operation to perform. Here is delete. Who should be deleted? What is deleted is the tag associated with the article.

	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 |
+-------------+---------+

 

 

Add using Append as above

---

	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

---

	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 []}]}