GORM不会创建多对多关联。

huangapple
go评论105阅读模式
英文:

GORM don't create many2many associations

问题

我有一个模型：

  1. type Book struct {
  2. 	gorm.Model
  3. 	Title       string `json:"title"`
  4. 	Author      string `json:"author"`
  5. 	Description string `json:"description"`
  6. 	Category    string `json:"Category"`
  7. 	Publisher   string `json:"publisher"`
  8. 	AuthorsCard []*AuthorsCard `gorm:"many2many:book_authorscard;" json:"authorscard"`
  9. }
  11. type AuthorsCard struct {
  12. 	gorm.Model
  13. 	Name        string `json:"name"`
  14. 	Age         int    `json:"age"`
  15. 	YearOfBirth int    `json:"year"`
  16. 	Biography   string `json:"biography"`
  17. }

在执行 db.AutoMigrate(&models.Book{}, &models.AuthorsCard{}) 后，我有一个创建函数：

  1. func TestCreate() {
  2. 	var testbook = models.Book{
  3. 		Title:  "Test",
  4. 		Author: "tst",
  5. 		AuthorsCard: []*models.AuthorsCard{
  6. 			{
  7. 				Age:         23,
  8. 				Name:        "test",
  9. 				YearOfBirth: 1999,
  10. 				Biography:   "23fdgsdddTEST",
  11. 			},
  12. 		},
  13. 		Description: "something",
  14. 	}
  15. 	db.Preload("AuthorsCard").Find(&models.Book{})
  17. 	db.Create(&testbook)
  19. }

尽管 AuthorsCard 中有一些数据，但我收到的响应是：

  1. {
  2.         "ID": 78,
  3.         "CreatedAt": "2022-06-23T13:10:58.01629+03:00",
  4.         "UpdatedAt": "2022-06-23T13:10:58.01629+03:00",
  5.         "DeletedAt": null,
  6.         "title": "Test",
  7.         "author": "tst",
  8.         "description": "something",
  9.         "Category": "",
  10.         "publisher": "",
  11.         "authorscard": null
  12.     }

如你所见，"authorscard" 是 null。

我该如何将 "authorscard" 保存到数据库中？
我使用的是 Gorm + PostgreSQL，我还用 Postman 发送了一些请求，结果都是一样的 - Authors card 是 null。

英文:

I have model:

  1. type Book struct {
  2. 	gorm.Model
  3. 	Title       string `json:"title"`
  4. 	Author      string `json:"author"`
  5. 	Description string `json:"description"`
  6. 	Category    string `json:"Category"`
  7. 	Publisher   string `json:"publisher"`
  8. 	AuthorsCard []*AuthorsCard `gorm:"many2many:book_authorscard; "json:"authorscard"`
  9. }
  11. type AuthorsCard struct {
  12. 	gorm.Model
  13. 	Name        string `json:"name"`
  14. 	Age         int    `json:"age"`
  15. 	YearOfBirth int    `json:"year"`
  16. 	Biography   string `json:"biography"`
  17. }

After db.AutoMigrate(&models.Book{}, &models.AuthorsCard{})
I have a creation function:

  1. func TestCreate() {
  2. 	var testbook = models.Book{
  3. 		Title:  "Test",
  4. 		Author: "tst",
  5. 		AuthorsCard: []*models.AuthorsCard{
  6. 			{
  7. 				Age:         23,
  8. 				Name:        "test",
  9. 				YearOfBirth: 1999,
  10. 				Biography:   "23fdgsdddTEST",
  11. 			},
  12. 		},
  13. 		Description: "something",
  14. 	}
  15. 	db.Preload("AuthorsCard").Find(&models.Book{})
  17. 	db.Create(&testbook)
  19. }

despite That AuthorsCard has some data in it, I receive this as a response:

  1. {
  2.         "ID": 78,
  3.         "CreatedAt": "2022-06-23T13:10:58.01629+03:00",
  4.         "UpdatedAt": "2022-06-23T13:10:58.01629+03:00",
  5.         "DeletedAt": null,
  6.         "title": "Test",
  7.         "author": "tst",
  8.         "description": "something",
  9.         "Category": "",
  10.         "publisher": "",
  11.         "authorscard": null
  12.     }

As you can see "authorscard" is null.

How can I save "authorscard" to the database?
I used Gorm + postgresql and also I sent a few request with postman, results are the same - Authors card is null

答案1

得分: 2

代码在正确的顺序下调用时是有效的：

  1. func TestCreate() {
  2.     db := getDB()
  3.     db.AutoMigrate(&Book{}, AuthorsCard{})
  5.     var testbook = Book{
  6.         Title:  "Test",
  7.         Author: "tst",
  8.         AuthorsCard: []*AuthorsCard{
  9.             {
  10.                 Age:         23,
  11.                 Name:        "test",
  12.                 YearOfBirth: 1999,
  13.                 Biography:   "23fdgsdddTEST",
  14.             },
  15.         },
  16.         Description: "something",
  17.     }
  19.     // 1. 创建 testbook。
  20.     db.Create(&testbook)
  22.     // 2. 将其存储到变量中：
  23.     var b1 *Book
  24.     db.Preload("AuthorsCard").Find(&b1)
  26.     fmt.Println(b1.AuthorsCard[0].Age)
  27.     fmt.Println(b1.AuthorsCard[0].Name)
  28.     fmt.Println(b1.AuthorsCard[0].YearOfBirth)
  29.     fmt.Println(b1.AuthorsCard[0].Biography)
  30. }

输出结果：

  1. > 23
  2. > test
  3. 1999
  4. 23fdgsdddTEST

此外，由于你传递了一个 AuthorsCard 的指针，并且在这些情况下编组不总是正常工作，所以你的 JSON 导出可能会失败。然而，GORM 在这里做得很好。

静态检查还给了我一些提示：

  1. type Book struct {
  2.     gorm.Model
  3.     Title       string         `json:"title"`
  4.     Author      string         `json:"author"`
  5.     Description string         `json:"description"`
  6.     Category    string         `json:"category"`
  7.     Publisher   string         `json:"publisher"`
  8.     AuthorsCard []*AuthorsCard `gorm:"many2many:book_authorscard" json:"authorscard"` // 错误的空格
  9. }
英文:

The code is working when it's called in the correct order:

  1. func TestCreate() {
  2. 	db := getDB()
  3. 	db.AutoMigrate(&Book{}, AuthorsCard{})
  5. 	var testbook = Book{
  6. 		Title:  "Test",
  7. 		Author: "tst",
  8. 		AuthorsCard: []*AuthorsCard{
  9. 			{
  10. 				Age:         23,
  11. 				Name:        "test",
  12. 				YearOfBirth: 1999,
  13. 				Biography:   "23fdgsdddTEST",
  14. 			},
  15. 		},
  16. 		Description: "something",
  17. 	}
  19.     // 1. Create your testbook.
  20. 	db.Create(&testbook)
  22.     // 2. Store it into a variable:
  23. 	var b1 *Book
  24. 	db.Preload("AuthorsCard").Find(&b1)
  25.     
  26. 	fmt.Println(b1.AuthorsCard[0].Age)
  27. 	fmt.Println(b1.AuthorsCard[0].Name)
  28. 	fmt.Println(b1.AuthorsCard[0].YearOfBirth)
  29. 	fmt.Println(b1.AuthorsCard[0].Biography)
  31. }

prints:

> 23
> test
1999
23fdgsdddTEST

Also your JSON export might fail since you pass a pointer to AuthorCard and the marshalling not always works properly in those cases. However, GORM does the right job here.

Static check also gave me some hints here:

  1. type Book struct {
  2. 	gorm.Model
  3. 	Title       string         `json:"title"`
  4. 	Author      string         `json:"author"`
  5. 	Description string         `json:"description"`
  6. 	Category    string         `json:"Category"`
  7. 	Publisher   string         `json:"publisher"`
  8. 	AuthorsCard []*AuthorsCard `gorm:"many2many:book_authorscard" json:"authorscard"` // wrong space
  9. }

huangapple
  • 本文由 发表于 2022年6月24日 17:02:08
  • 转载请务必保留本文链接：https://go.coder-hub.com/72741544.html
  • go
  • go-gorm
  • postgresql
  • postman
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