指定`gorm:”unique”`会导致预加载属于关系的问题。

huangapple
go评论117阅读模式
英文:

Specifying `gorm:"unique"`, causing preload of belongs to relation a problem

问题

这是我的帖子和用户结构模型：

  1. type Post struct {
  2.     ID     string `gorm:"primaryKey"`
  3.     Title  string `gorm:"unique"`
  4.     UserID string
  5.     User   User
  6. }
  8. type User struct {
  9.     ID   string `gorm:"primaryKey"`
  10.     Name string
  11. }
  13. // 创建一个具有标题和用户输入的帖子的代码
  14. func CreatePost(title string, u User) (Post, error) {
  15.     b := Post{Title: title, User: u}
  16.     dbIns := GetDB()
  17.     if err := dbIns.Create(&b).Error; err != nil {
  18.         return Post{}, err
  19.     }
  20.     return b, nil
  21. }
  23. // 获取帖子的代码，同时预加载其用户字段
  24. func GetOnePost() (Post, error) {
  25.     var p Post
  26.     dbIns := GetDB()
  27.     if err := dbIns.Model(&Post{}).Preload("User").First(&p).Error; err != nil {
  28.         return Post{}, err
  29.     }
  30.     return p, nil
  31. }

这是从GetOnePost()获得的输出，正是我所期望的，Post.User不为空。

  1. 2022/11/27 15:42:48 帖子标题：John-Doe的标题，UUID：32158510-6dcc-4c26-bcb8-7d76a88bda72，作者UUID：73d020d3-eb8d-4bf7-9f57-e821c5deceed
  2. 2022/11/27 15:42:48 用户名：John-Doe，UUID：73d020d3-eb8d-4bf7-9f57-e821c5deceed

然而，当我将User.Name指定为唯一时（因为我希望每个用户具有不同的名称），GetOnePost()的输出发生了变化。请忽略UUID。

  1. 2022/11/27 15:57:49 帖子标题：John-Doe的标题，UUID：26355816-c376-497a-a250-be118c5933e2，作者UUID：e858cd72-56b9-4884-b6e6-94121c36719b
  2. 2022/11/27 15:57:49 用户名：，UUID：

问题在于，当我向User模型添加唯一约束时，返回的Post.User似乎为空。如果我从User模型中删除唯一约束，它就恢复正常（Post.User非空）。所以我认为问题出在gorm:"unique"这部分。

英文:

Here's my Post & User struct model :

  1. type Post struct {
  2.     ID     string `gorm:"primaryKey"`
  3.     Title  string `gorm:"unique"`
  4.     UserID string
  5.     User   User
  6. }
  9. type User struct {
  10.     ID   string `gorm:"primaryKey"`
  11.     Name string
  12. }
  14. // Code to create a Post with title & user input
  15. func CreatePost(title string, u User) (Post, error) {
  16. 	b := Post{Title: title, User: u}
  17. 	dbIns := GetDB()
  18. 	if err := dbIns.Create(&b).Error; err != nil {
  19. 		return Post{}, err
  20. 	}
  21. 	return b, nil
  22. }
  24. // Code to get a Post, also preload its User field
  25. func GetOnePost() (Post, error) {
  26. 	var p Post
  27. 	dbIns := GetDB()
  28. 	if err := dbIns.Model(&Post{}).Preload("User").First(&p).Error; err != nil {
  29. 		return Post{}, err
  30. 	}
  31. 	return p, nil
  32. }

Here's is an output of what I got from GetOnePost(), which is exactly what I expected, Post.User is not empty.

  1. 2022/11/27 15:42:48 Post title: John-Doe's Title, UUID: 32158510-6dcc-4c26-bcb8-7d76a88bda72, authorUUID: 73d020d3-eb8d-4bf7-9f57-e821c5deceed 
  2. 2022/11/27 15:42:48 User name: John-Doe, UUID: 73d020d3-eb8d-4bf7-9f57-e821c5deceed

However when I specified the User.Name to be unique (since I want each user to have different Name)<br/>
note : yes I did migrate into a new table.

  1. type User struct {
  2. 	ID   string `gorm:&quot;primaryKey&quot;`
  3. 	Name string `gorm:&quot;unique&quot;`
  4. }

The output from GetOnePost() changed to this : (please ignore the UUID)

  1. 2022/11/27 15:57:49 Post title: John-Doe&#39;s Title, UUID: 26355816-c376-497a-a250-be118c5933e2, authorUUID: e858cd72-56b9-4884-b6e6-94121c36719b 
  2. 2022/11/27 15:57:49 User name: , UUID:

A problem is that the returned Post.User seems to be empty, when I add unique constraint to User model.

If I remove the unique constraint from User model, it returns to normal (Post.User not-empty). So it seems to me that the problem is with the gorm:"unique" part.

答案1

得分: 1

老实说，我无法重现你的问题。不过，我添加了我尝试重现你的问题的代码，它按预期工作。首先让我展示代码，然后我会给你一个简要的解释：

  1. package main
  3. import (
  4. 	"fmt"
  6. 	"gorm.io/driver/postgres"
  7. 	"gorm.io/gorm"
  9. 	"github.com/google/uuid"
  10. 	_ "github.com/lib/pq"
  11. )
  13. type Post struct {
  14. 	ID     string `gorm:"primaryKey"`
  15. 	Title  string `gorm:"unique"`
  16. 	UserID string
  17. 	User   User
  18. }
  20. type User struct {
  21. 	ID   string `gorm:"primaryKey"`
  22. 	Name string `gorm:"unique"`
  23. }
  25. // 创建一个带有标题和用户输入的帖子的代码
  26. func CreatePost(db *gorm.DB, title string, u User) (Post, error) {
  27. 	id := uuid.NewString()
  28. 	b := Post{ID: id, Title: title, User: u}
  29. 	if err := db.Create(&b).Error; err != nil {
  30. 		return Post{}, err
  31. 	}
  32. 	return b, nil
  33. }
  35. // 获取一篇帖子的代码，同时预加载其User字段
  36. func GetOnePost(db *gorm.DB) (Post, error) {
  37. 	var p Post
  38. 	if err := db.Model(&Post{}).Preload("User").First(&p).Error; err != nil {
  39. 		return Post{}, err
  40. 	}
  41. 	return p, nil
  42. }
  44. func main() {
  45. 	dsn := "host=localhost user=postgres password=postgres dbname=postgres port=5432 sslmode=disable"
  46. 	db, err := gorm.Open(postgres.Open(dsn), &gorm.Config{})
  47. 	if err != nil {
  48. 		panic(err)
  49. 	}
  51. 	db.AutoMigrate(&User{})
  52. 	db.AutoMigrate(&Post{})
  54. 	defer db.Exec("DROP TABLE users")
  55. 	defer db.Exec("DROP TABLE posts")
  57. 	userId := uuid.NewString()
  59. 	_, err = CreatePost(db, "Learn Go", User{
  60. 		ID:   userId,
  61. 		Name: "John Doe",
  62. 	})
  63. 	if err != nil {
  64. 		panic(err)
  65. 	}
  67. 	post, err := GetOnePost(db)
  68. 	if err != nil {
  69. 		panic(err)
  70. 	}
  72. 	// 这会导致数据库中的重复错误 SQLSTATE 23505
  73. 	// if err := db.Create(&User{
  74. 	// 	ID:   uuid.NewString(),
  75. 	// 	Name: "John Doe",
  76. 	// }).Error; err != nil {
  77. 	// 	panic(err)
  78. 	// }
  80. 	fmt.Printf("帖子的详细信息：%v\n", post)
  81. }

代码基本上与你提供的代码相同。我添加了两个延迟函数调用，以便在每次运行代码后删除表。通过这样做，我们始终确保使用最新的表定义。然后，我在Postgres中检查了UNIQUE约束是否存在，并且我正确地找到了它。然而，当我尝试运行我的代码时，我成功地能够检索到User信息。如果你尝试取消注释以// this leads to a Duplicate error SQLSTATE 23505 in DB开头的代码块，你将会得到一个重复错误，因此约束在数据库端得到了执行。

如果你使用我的解决方案，让我知道你的代码是否也能正常工作！

英文:

Honestly, I was not able to repro your issue. Anyway, I added my attempt to repro your issue that works as expected. Let me show the code first and then I'll provide you with a brief explanation:

  1. package main
  3. import (
  4. 	&quot;fmt&quot;
  6. 	&quot;gorm.io/driver/postgres&quot;
  7. 	&quot;gorm.io/gorm&quot;
  9. 	&quot;github.com/google/uuid&quot;
  10. 	_ &quot;github.com/lib/pq&quot;
  11. )
  13. type Post struct {
  14. 	ID     string `gorm:&quot;primaryKey&quot;`
  15. 	Title  string `gorm:&quot;unique&quot;`
  16. 	UserID string
  17. 	User   User
  18. }
  20. type User struct {
  21. 	ID   string `gorm:&quot;primaryKey&quot;`
  22. 	Name string `gorm:&quot;unique&quot;`
  23. }
  25. // Code to create a Post with title &amp; user input
  26. func CreatePost(db *gorm.DB, title string, u User) (Post, error) {
  27. 	id := uuid.NewString()
  28. 	b := Post{ID: id, Title: title, User: u}
  29. 	if err := db.Create(&amp;b).Error; err != nil {
  30. 		return Post{}, err
  31. 	}
  32. 	return b, nil
  33. }
  35. // Code to get a Post, also preload its User field
  36. func GetOnePost(db *gorm.DB) (Post, error) {
  37. 	var p Post
  38. 	if err := db.Model(&amp;Post{}).Preload(&quot;User&quot;).First(&amp;p).Error; err != nil {
  39. 		return Post{}, err
  40. 	}
  41. 	return p, nil
  42. }
  44. func main() {
  45. 	dsn := &quot;host=localhost user=postgres password=postgres dbname=postgres port=5432 sslmode=disable&quot;
  46. 	db, err := gorm.Open(postgres.Open(dsn), &amp;gorm.Config{})
  47. 	if err != nil {
  48. 		panic(err)
  49. 	}
  51. 	db.AutoMigrate(&amp;User{})
  52. 	db.AutoMigrate(&amp;Post{})
  54. 	defer db.Exec(&quot;DROP TABLE users&quot;)
  55. 	defer db.Exec(&quot;DROP TABLE posts&quot;)
  57. 	userId := uuid.NewString()
  59. 	_, err = CreatePost(db, &quot;Learn Go&quot;, User{
  60. 		ID:   userId,
  61. 		Name: &quot;John Doe&quot;,
  62. 	})
  63. 	if err != nil {
  64. 		panic(err)
  65. 	}
  67. 	post, err := GetOnePost(db)
  68. 	if err != nil {
  69. 		panic(err)
  70. 	}
  72. 	// this leads to a Duplicate error SQLSTATE 23505 in DB
  73. 	// if err := db.Create(&amp;User{
  74. 	// 	ID:   uuid.NewString(),
  75. 	// 	Name: &quot;John Doe&quot;,
  76. 	// }).Error; err != nil {
  77. 	// 	panic(err)
  78. 	// }
  80. 	fmt.Printf(&quot;post&#39;s details: %v\n&quot;, post)
  81. }

More or less the code is the same as you provided. I added two deferred function calls to delete the tables after every run of the code. Thanks to this we're always sure to work with the latest table definition provided. Then, I check in Postgres if the UNIQUE constraint was present and I correctly found it. However, when I try to run my code I was successfully able to retrieve also the User information. If you try to uncomment the code block starting with this comment // this leads to a Duplicate error SQLSTATE 23505 in DB you'll get a duplicate error so the constraint is enforced on the database side.

Let me know if by using my solution your code works too!

huangapple
  • 本文由 发表于 2022年11月27日 11:06:58
  • 转载请务必保留本文链接：https://go.coder-hub.com/74587204.html
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  • go
  • go-gorm
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