sql - 如何在 gorm 中创建外键？

Question

所以我在应用程序中有两个表:users 和 posts。我想实现一个用户可以喜欢帖子的喜欢功能。为此，我创建了下表:

type Like struct {
    PostId    string    `json:"post_id"`
    UserId    string    `json:"user_id"`
    CreatedAt time.Time `json:"created_at"`
}

我的问题是当我AutoMigrate Like 模型时，我怎样才能自动设置外键？

我已经尝试在各自的位置使用 gorm:"foreignKey:Post" 和 gorm:"foreignKey:User" 结构标签但他们什么都不做。

我怎样才能让它发挥作用？谢谢!

Answer 1

由于您在命名时没有遵循约定(即 Id 而不是 ID，PostId 而不是 PostID)，您需要明确告诉 gorm 哪个是外键并引用哪个属性。

这是片段。 Github Link

引用:

1. Belongs To
2. Has Many

package storage2

import (
    "log"

    "gorm.io/driver/sqlite"
    "gorm.io/gorm"
    "gorm.io/gorm/logger"
)

type Post struct {
    Body   string `gorm:"type:text"`
    Id     string `gorm:"type:uuid;primary_key"`
    Likes  []Like `gorm:"foreignkey:PostId;references:Id"`
    User   User   `gorm:"foreignkey:UserId;references:Id"`
    UserId string
}

type Like struct {
    Id     string `gorm:"type:uuid;primary_key"`
    PostId string `gorm:"type:uuid;not null"`
    User   User   `gorm:"foreignkey:UserId;references:Id"`
    UserId string
}

type User struct {
    Id   string `gorm:"type:uuid;primary_key"`
    Name string
}

func GormTest() {
    db, err := gorm.Open(sqlite.Open("gorm.db"), &gorm.Config{
        Logger: logger.Default.LogMode(logger.Info),
    })
    if err != nil {
        log.Fatal("could not open database")
    }
    err = db.AutoMigrate(&User{}, &Post{}, &Like{})
    if err != nil {
        log.Fatal("could not migrate database")
    }
    createTestData(db)
    fetchData(db)
}

func createTestData(db *gorm.DB) {
    users := []User{
        {Id: "0b83313d-1f85-4093-8621-efd2f21419d3", Name: "Shahriar"},
        {Id: "bddd6566-bcd2-4ad1-8eb9-65a23f5a9856", Name: "John"},
        {Id: "663c1328-dce2-4527-aecb-7fc478c229c2", Name: "Durand"}}
    err := db.Create(&users).Error
    if err != nil {
        log.Println("failed to create user data")
    }
    like := Like{
        Id:     "45ba45fc-0900-4fcc-80dd-c394170b777b",
        UserId: users[0].Id,
    }
    post := Post{
        Id:     "4cebb4c7-d44e-4160-a2df-a06f43211d45",
        Body:   "Test Post",
        Likes:  []Like{like},
        UserId: users[1].Id,
    }
    err = db.Create(&post).Error
    if err != nil {
        log.Println("failed to crete post")
    }
}

func fetchData(db *gorm.DB) {
    post := Post{
        Id: "4cebb4c7-d44e-4160-a2df-a06f43211d45",
    }
    if err := db.Preload("Likes").First(&post).Error; err != nil {
        log.Println("failed to load post")
    }
    log.Println(post)
}