在GORM中组合2个或更多模型来生成 struct 结果的最佳方式是什么？
给定这些示例模型:
type Book struct {
gorm.Model
Title string
Description string
AuthorID uint
}
type Author struct {
gorm.Model
FirstName string
LastName string
Books []Book
}
我想创建一个按标题查找图书的查询
db.Where("title=?", "foo").Find(&books)
到目前为止没有问题，但我还想在结果中包括Author.FirstName和Author.LastName.这不适用于我try 过的任何方法，因为Book Struct不包括这些字段.期望的结果应该包括来自匹配图书的所有字段，以及来自与该图书相关的作者的所有字段.
try 使用Select()和Join()函数来指定所有所需的字段，这会生成正确的SQL语句，但生成的Book struct 仍然不包含任何Author字段.
I was able to accomplish your request in this way.
First, I added Author Author field to the Book struct. In this way, you can save the information of the author together with his books.
In the query, you've to use Preload("Auhtor") to let GORM load also the information from the authors table. This practice is called eager-loading. Below, you can find my working solution:
package main
import (
"fmt"
"gorm.io/driver/postgres"
"gorm.io/gorm"
)
type Book struct {
gorm.Model
Title string
Description string
AuthorID uint
Author Author
}
type Author struct {
gorm.Model
FirstName string
LastName string
Books []Book
}
func main() {
dsn := "host=localhost user=postgres password=postgres dbname=postgres port=5432 sslmode=disable"
db, err := gorm.Open(postgres.Open(dsn), &gorm.Config{})
if err != nil {
panic(err)
}
db.AutoMigrate(&Book{})
db.AutoMigrate(&Author{})
book1 := &Book{Title: "Go", Description: "Intro to Golang", AuthorID: 1}
book2 := &Book{Title: "GORM", Description: "Intro to GORM", AuthorID: 1}
author := &Author{FirstName: "John", LastName: "Doe", Books: []Book{*book1, *book2}}
db.Create(author)
var books []Book
db.Preload("Author").Where("title=?", "Go").Find(&books)
for _, v := range books {
fmt.Println("book 1:")
fmt.Printf("title: %q\n\n", v.Title)
fmt.Printf("author details:\n")
fmt.Printf("first name: %q\n", v.Author.FirstName)
fmt.Printf("last name: %q\n", v.Author.LastName)
}
}
希望这能帮助你理解.