invalid field found for struct test/entity.UserEntity's - go

Question

I'm really new to go and I decided to create a RestAPI for skill practising. So now I'm trying to make a one to many relationship between my User and Book entities. But when I try to save my Book entity to database, it shows me such error:
invalid field found for struct test/entity.UserEntity's field Books: define a valid foreign key for relations or implement the Valuer
/Scanner interface
Here's my code:
UserEntity
type UserEntity struct {
gorm.Model
Username string `gorm:"unique;not null"`
Email string `gorm:"unique;not null"`
Password string `gorm:"not null"`
Books []BookEntity `gorm:"constraint:OnUpdate:CASCADE,OnDelete:SET NULL;"`
}
func (*UserEntity) TableName() string {
return "users"
}
BookEntity
type BookEntity struct {
gorm.Model
Name string `gorm:"not null"`
Isbn int `gorm:"unique;not null"`
AuthorID uint
}
func (*BookEntity) TableName() string {
return "books"
}
BookAddModel
type BookAddModel struct {
Name string `json:"name"`
Isbn int `json:"isbn"`
}
func (bookModel *BookAddModel) ToModel(ctx *gin.Context) {
ctx.Bind(&bookModel)
}
Here's the code where I add entities to database
func AddBook(bookModel models.BookAddModel, author *entity.UserEntity) entity.BookEntity {
var book entity.BookEntity
mapstructure.Decode(bookModel, &book)
config.DbSession.Create(&book) // <<<< here's error
author.Books = append(author.Books, book)
config.DbSession.Save(author)
return book
}
Config
var DbSession *gorm.DB
var PostgresData = "host=localhost user=postgres password=4122 dbname=gorm port=5432 sslmode=disable TimeZone=Asia/Shanghai"
So what can bee the problem? If you know, please tell me. I'd really appreciate it!

Answer 1

You should set foreignKey for UserEntity.Books:
type UserEntity struct {
...
Books []BookEntity `gorm:"foreignKey:AuthorID,..."`
}
Just don't forget to drop tables first and rerun AutoMigrations:
db.AutoMigrate(&UserEntity{})
db.AutoMigrate(&BookEntity{})