恐慌：反射：在 GORM .Create() 上调用 reflect.Value.Interface 的零值。

huangapple
go评论122阅读模式
英文:

panic: reflect: call of reflect.Value.Interface on zero Value on GORM .Create()

问题

我是你的中文翻译助手，以下是你要翻译的内容：

我刚开始学习Go和后端开发，我正在尝试在表之间建立多对多的关系。我使用了这个仓库来创建模型：https://github.com/harranali/gorm-relationships-examples/tree/main/many-to-many
我使用的是GORM和PostgreSQL。
我的模型如下：

  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. }

在连接到数据库并进行自动迁移后：

  1. func init() {
  2. 	config.Connect()
  3. 	db = config.GetDB()
  4. 	db.AutoMigrate(&models.Book{}, &models.AuthorsCard{})
  5. }

我创建了一个函数来查看这个关系是如何工作的：

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

但是出现了以下错误：
panic: reflect: call of reflect.Value.Interface on zero Value [recovered]
panic: reflect: call of reflect.Value.Interface on zero Value

我该如何处理这个"Null"问题并建立正确的关系？

**更新：**问题的第一部分与GORM的版本有关。在将旧版本(github.com/jinzhu/gorm v1.9.16)更改为新版本(gorm.io/gorm v1.23.6)后，reflect错误的问题消失了。但是现在，当我想创建新的书籍时，出现了以下错误：

/go/pkg/mod/gorm.io/driver/postgres@v1.3.7/migrator.go:119 ERROR: there is no unique constraint matching given keys for referenced table "authors_cards" (SQLSTATE 42830)
[28.440ms] [rows:0] CREATE TABLE "book_authorscard" ("book_id" bigint,"authors_card_id" bigint,PRIMARY KEY ("book_id","authors_card_id"),CONSTRAINT "fk_book_authorscard_authors_card" FOREIGN KEY ("authors_card_id") REFERENCES "authors_cards"("id"),CONSTRAINT "fk_book_authorscard_book" FOREIGN KEY ("book_id") REFERENCES "books"("id"))
[GIN-debug] [WARNING] Creating an Engine instance with the Logger and Recovery middleware already attached.

**更新2：**我决定使用Migrator().DropTable()来删除表，这样做有点奏效，所有的错误都消失了。但是我仍然得到"authorscard": null作为响应。

英文:

I'm new to go and Backend and I'm Trying to make many-to-many relation between tables. I used this repo to make model:https://github.com/harranali/gorm-relationships-examples/tree/main/many-to-many
I Used GORM with postgresql.
My 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:"many-to-many: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 connecting to database and AutoMigrating:

  1. func init() {
  2. 	config.Connect()
  3. 	db = config.GetDB()
  4. 	db.AutoMigrate(&models.Book{}, &models.AuthorsCard{})
  5. }

I've created Function to see how that relation works:

  1. func TestCreate() {
  3. var AuthorsCard = []models.AuthorsCard{
  4. 		{
  5. 			Age:         23,
  6. 			Name:        "test",
  7. 			YearOfBirth: 1999,
  8. 			Biography:   "23fdgsdddTEST",
  9. 		},
  10. 	}
  11. 	db.Create(&AuthorsCard)
  12. 	var testbook = models.Book{
  13. 		Title:       "Test",
  14. 		Author:      "tst",
  15. 		Description: "something",
  16. 	}
  17. 	db.Create(&testbook)
  19. 	db.Model(&testbook).Association("AuthorsCard").Append(&AuthorsCard)
  20. }

But got This Error:
panic: reflect: call of reflect.Value.Interface on zero Value [recovered]
panic: reflect: call of reflect.Value.Interface on zero Value

How can I deal with this "Null" problem and make proper relation?

UPD: The First part of a problem was connected to a version of GORM, After I changed old version(github.com/jinzhu/gorm v1.9.16) to new version (gorm.io/gorm v1.23.6) the problem with reflect Error gone.
but now, when I want to create new book, I get this Error:

/go/pkg/mod/gorm.io/driver/postgres@v1.3.7/migrator.go:119 ERROR: there is no unique constraint matching given keys for referenced table "authors_cards" (SQLSTATE 42830)
[28.440ms] [rows:0] CREATE TABLE "book_authorscard" ("book_id" bigint,"authors_card_id" bigint,PRIMARY KEY ("book_id","authors_card_id"),CONSTRAINT "fk_book_authorscard_authors_card" FOREIGN KEY ("authors_card_id") REFERENCES "authors_cards"("id"),CONSTRAINT "fk_book_authorscard_book" FOREIGN KEY ("book_id") REFERENCES "books"("id"))
[GIN-debug] [WARNING] Creating an Engine instance with the Logger and Recovery middleware already attached.

UPD 2:
I decided to make a Migrator().DropTable(). That's kinda worked, and all Errors have gone. But still I get "authorscard": null as a response.

答案1

得分: 1

通过阅读 Gorm v2 的发布说明（https://gorm.io/docs/v2_release_note.html），我认为你正在尝试使用一个旧版本（<v2）的 Gorm 来使用 v2 的功能。请尝试使用 Gorm 的最新版本。

英文:

By reading the release note of Gorm v2 (https://gorm.io/docs/v2_release_note.html), I think that you are trying to use v2 feature with an old version (<v2). Try to use Gorm latest version.

huangapple
  • 本文由 发表于 2022年6月23日 18:39:00
  • 转载请务必保留本文链接：https://go.coder-hub.com/72728791.html
  • go
  • go-gorm
  • postgresql
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