gorm的related理解和实例

package main

import (
	"fmt"

	_ "github.com/go-sql-driver/mysql"
	"github.com/jinzhu/gorm"
)

var (
	dev_db   = "aplum:plum2016@tcp(localhost:3306)/aplum?charset=utf8"
	local_db = "root:123456@tcp(localhost:3306)/test?charset=utf8"
)

type MyUser struct {
	ID   int `gorm:"TYPE:int(11);NOT NULL;PRIMARY_KEY;INDEX"`
	Name string
}

type MyProfile struct {
	ID        int `gorm:"TYPE:int(11);NOT NULL;PRIMARY_KEY;INDEX"`
	Name      string
	User      MyUser `gorm:"foreignkey:UserRefer"`
	UserRefer uint
}

func main() {
	db, err := gorm.Open("mysql", local_db)
	db.LogMode(true)

	if err != nil {
		panic(err)
	}
	defer db.Close()
	related(db)
}

func setData(db *gorm.DB) {
	db.Debug().AutoMigrate(&MyUser{})
	db.Debug().AutoMigrate(&MyProfile{})
	db.Debug().Create(&MyUser{ID: 1, Name: "uname1"})
	db.Debug().Create(&MyUser{ID: 2, Name: "uname2"})
	db.Debug().Create(&MyProfile{ID: 11, Name: "pname2", UserRefer: 1})
	db.Debug().Create(&MyProfile{ID: 22, Name: "pname2", UserRefer: 2})
}

func related(db *gorm.DB) {
	var profile MyProfile
	db.Debug().First(&profile)
	fmt.Println(fmt.Sprintf("%+v", profile))
	db.Model(&profile).Related(&profile.User, "UserRefer")
	fmt.Println(fmt.Sprintf("%+v", profile))
}

gorm的tag foreignkey就是图中的 foreignkey，
tag ASSOCIATION_FOREIGNKEY 就是图中的references。

定义外健约束的2个关键字，翻译到gorm的用法就是gorm:"FOREIGNKEY:UserId;ASSOCIATION_FOREIGNKEY:ID"。

有如下结构:

type User struct {
    gorm.Model
    Name string
    Company []Company
}

type Company struct {
    gorm.Model
    Job    string
    User   User
    UserID int
}


    var user User
    var company []Company

    user.ID = 1

    db.Model(&user).Related(&company)
    db.Model(&user).Association("company").Find(&company)

使用Related和Association都可以查询出来关联的company的数据.那他们的差异是什么呢?### 题目描述

二者区别在于谁主谁从
下述代码中user表是源，company关联源中的字段名，简而言之通过先查user-->commpany 最终的主表记录从user出发

    db.Model(&user).Association("company").Find(&company)

而Related方法其内的company表是要查主表源，主查company表user实例只是条件填充对象

db.Model(&user).Related(&company)
//// SELECT * FROM company WHERE user_id = 1; // 1 is user's primary key

开启sql打印一目了然

// 启用Logger，显示详细日志
db.LogMode(true)