GORM 不会创建很多 2many 关联

Question

我有模型:

type Book struct {
gorm.Model
Title       string `json:"title"`
Author      string `json:"author"`
Description string `json:"description"`
Category    string `json:"Category"`
Publisher   string `json:"publisher"`
AuthorsCard []*AuthorsCard `gorm:"many2many:book_authorscard; "json:"authorscard"`
}
type AuthorsCard struct {
gorm.Model
Name        string `json:"name"`
Age         int    `json:"age"`
YearOfBirth int    `json:"year"`
Biography   string `json:"biography"`
}

db.AutoMigrate后(及模型。
我有一个创建函数:

func TestCreate() {
var testbook = models.Book{
Title:  "Test",
Author: "tst",
AuthorsCard: []*models.AuthorsCard{
{
Age:         23,
Name:        "test",
YearOfBirth: 1999,
Biography:   "23fdgsdddTEST",
},
},
Description: "something",
}
db.Preload("AuthorsCard").Find(&models.Book{})
db.Create(&testbook)
}

尽管AuthorsCard有一些数据在它，我收到这个作为响应:

{
"ID": 78,
"CreatedAt": "2022-06-23T13:10:58.01629+03:00",
"UpdatedAt": "2022-06-23T13:10:58.01629+03:00",
"DeletedAt": null,
"title": "Test",
"author": "tst",
"description": "something",
"Category": "",
"publisher": "",
"authorscard": null
}

可以看到"authorscard"是零。

如何保存"authorscard"到数据库?我使用Gorm + postgresql，也用邮差发送了一些请求，结果是一样的-作者卡是空的

Answer 1

当按正确顺序调用时，代码正在工作:

func TestCreate() {
db := getDB()
db.AutoMigrate(&Book{}, AuthorsCard{})
var testbook = Book{
Title:  "Test",
Author: "tst",
AuthorsCard: []*AuthorsCard{
{
Age:         23,
Name:        "test",
YearOfBirth: 1999,
Biography:   "23fdgsdddTEST",
},
},
Description: "something",
}
// 1. Create your testbook.
db.Create(&testbook)
// 2. Store it into a variable:
var b1 *Book
db.Preload("AuthorsCard").Find(&b1)

fmt.Println(b1.AuthorsCard[0].Age)
fmt.Println(b1.AuthorsCard[0].Name)
fmt.Println(b1.AuthorsCard[0].YearOfBirth)
fmt.Println(b1.AuthorsCard[0].Biography)
}

打印:

23测试199923 fdgsdddtest

你的JSON导出也可能失败，因为你传递了一个指向AuthorCard的指针，在这些情况下，编组并不总是正常工作。然而，GORM在这里做得很好。

静态检查也给了我一些提示:

type Book struct {
gorm.Model
Title       string         `json:"title"`
Author      string         `json:"author"`
Description string         `json:"description"`
Category    string         `json:"Category"`
Publisher   string         `json:"publisher"`
AuthorsCard []*AuthorsCard `gorm:"many2many:book_authorscard" json:"authorscard"` // wrong space
}