Gorm 关联的使用

创建关联，进行关联操作，以及查询关联表数据

Go代码演示

数据类型定义

type User struct {
    Id int64
    Name string
    Address string
    Phone string
    Orders []*Order
}

type Order struct {
    Id int64
    Amount int64
    CreateAt int64
    Goods []*Good
    UserId int64
}

type Good struct {
    Id int64
    Name string
    Price int64
    OrderId int64
}

//go run main.go
package main

import (
    "gorm.io/driver/sqlite"
    "gorm.io/gorm"
    "gorm.io/gorm/clause"
    "log"
    "time"
)

//使用一对多模型创建关联
//一个用户有多个订单，一个订单有多个商品
//一个用户包含很多订单，一个订单包含很多商品
type User struct {
    Id int64
    Name string
    Address string
    Phone string
    Orders []*Order
}

type Order struct {
    Id int64
    Amount int64
    CreateAt int64
    Goods []*Good
    UserId int64
}

type Good struct {
    Id int64
    Name string
    Price int64
    OrderId int64
}

func main()  {
    //链接数据库
    db, err := gorm.Open(sqlite.Open("gorm.db"), &gorm.Config{})
    if err != nil {
        panic(err)
    }
    //迁移表
    err = db.AutoMigrate(&User{}, &Order{}, &Good{})
    if err != nil {
        panic(err)
    }
    //初始化关联数据
    user := new(User)
    user.Name = "guojinfei"
    user.Address = "北京64胡同12号"
    user.Phone = "15311119999"
    user.Orders = []*Order{
        &Order{
            Amount: 1664,
            CreateAt: time.Now().Unix(),
            Goods: []*Good{
                &Good{
                    Name:    "雪梨",
                    Price:   128,
                },
            },
        },
    }
    //创建数据，自动创建关联
    tx := db.Create(&user)
    tx = db.Save(&user)
    if tx.Error != nil {
        panic(err)
    }
    //查询关联订单数
    count := db.Model(&User{Id: 2}).Association("Orders").Count()
    log.Println("count:", count)
    //查询用户的订单所购买的商品
    var orders []Order
    var goods []Good
    err = db.Model(&User{Id: 2}).Association("Orders").Find(&orders)
    if err != nil {
        panic(err)
    }
    err = db.Model(&orders).Association("Goods").Find(&goods)
    if err != nil {
        panic(err)
    }
    log.Println("orders:", orders)
    log.Println("goods:", goods)
    //删除关联
    db.Select("Orders", "Goods").Delete(&User{Id: 6})
    db.Select(clause.Associations).Delete(&User{Id: 7})
}

//输出：
//count: 2
//orders: [{2 1664 1653532944 [] 2} {3 1664 1653533385 [] 2}]
//goods: [{2 雪梨 128 2} {3 雪梨 128 3}]

数据表展示

-- auto-generated definition
create table users
(
    id      integer
        primary key,
    name    text,
    address text,
    phone   text
);


-- auto-generated definition
create table orders
(
    id        integer
        primary key,
    amount    integer,
    create_at integer,
    user_id   integer
        constraint fk_users_orders
            references users
);


-- auto-generated definition
create table goods
(
    id       integer
        primary key,
    name     text,
    price    integer,
    order_id integer
        constraint fk_orders_goods
            references orders
);

Orm关联的设计提供了对关联模型的操作手段，对于关联模型的数据迁移和关联模型数据操作的一致性是需要用户去保证的

文档参考

Gorm关联 https://gorm.io/zh_CN/docs/belongs_to.html