ORM框架Gorm-Has One

has one 与另一个模型建立一对一的关联，但它和一对一关系有些许不同。 这种关联表明一个模型的每个实例都包含或拥有另一个模型的一个实例。

type Cat struct {
	gorm.Model
	Name string
	Toy  Toy `gorm:"polymorphic:Owner"`
}

type Dog struct {
	gorm.Model
	Name string
	Toy  Toy `gorm:"polymorphic:Owner"`
}

type Toy struct {
	gorm.Model
	Name     string
	OwnerID  int
	OwerType string
}

var db *gorm.DB

func init() {
	dsn := "root:root@tcp(127.0.0.1:3306)/go_orm?charset=utf8mb4&parseTime=True&loc=Local"
	d, err := gorm.Open(mysql.Open(dsn), &gorm.Config{})
	if err != nil {
		log.Fatal(err)
	}
	db = d
	db.AutoMigrate(&Cat{}, &Dog{}, &Toy{})
}

func CreateTestData() {
	db.Create(&Dog{Name: "dog1", Toy: Toy{Name: "dog1-toy1"}})
	db.Create(&Dog{Name: "dog2", Toy: Toy{Name: "dog2-toy2"}})
	db.Create(&Dog{Name: "dog3"})
	db.Create(&Cat{Name: "cat1", Toy: Toy{Name: "cat1-toy1"}})
}

func testSelect4() {
	var dogs []Dog
	db.Preload("Toy").Find(&dogs)
	for _, dog := range dogs {
		fmt.Printf("dog.Name: %vn", dog.Name)
		fmt.Printf("dog.Toy.Name: %vn", dog.Toy.Name)
	}
	fmt.Println("----------------------------------------------------------")
	var cats []Cat
	db.Preload("Toy").Find(&cats)
	for _, cat := range cats {
		fmt.Printf("cat.Name: %vn", cat.Name)
		fmt.Printf("cat.Toy.Name: %vn", cat.Toy.Name)
	}
}

运行结果如下

查找1,3的数据，因为1有关联3没有关联

func findAssociation(id uint) {
	var dog1 Dog
	db.Model(&Dog{}).Where("id", id).Find(&dog1)
	fmt.Printf("dog1.Name: %vn", dog1.Name)
	var toy11 Toy
	db.Model(&dog1).Association("Toy").Find(&toy11)
	fmt.Printf("toy11.Name: %vn", toy11.Name)
	fmt.Println("----------------------------------------------------------")
}
findAssociation(1)
findAssociation(3)

运行结果如下

给id为3添加一个关联

func addAssociation() {
	var dog3 Dog
	db.Model(&Dog{}).Where("id", 3).Find(&dog3)
	db.Model(&dog3).Association("Toy").Append(&Toy{Name: "dog3-add-toy"})
}

运行结果

把dog的id为1的玩具替换为新的玩具

func replaceAssociation() {
	var dog1 Dog
	db.Model(&Dog{}).Where("id", 1).Find(&dog1)
	db.Model(&dog1).Association("Toy").Replace(&Toy{Name: "dog1--new-toy1"})
}

运行结果

查询dogi的id为1的玩具个数，因为是一对一所有个数是1或者0,0是没有添加对应的玩具

func countAssociation() {
	var dog1 Dog
	db.Model(&Dog{}).Where("id", 1).Find(&dog1)
	i := db.Model(&dog1).Association("Toy").Count()
	fmt.Printf("i: %vn", i)
}

运行结果

删除dog的id为2的玩具对应玩具表id也是2，之前创建时候刚好对应上

func deleteAssociation() {
	var dog2 Dog
	db.Model(&Dog{}).Where("id", 2).Find(&dog2)
	var toy Toy
	db.Model(&Toy{}).Where("id", 2).Find(&toy)
	db.Model(&dog2).Association("Toy").Delete([]Toy{toy})
}

运行结果

func clearAssociation() {
	var dog1 Dog
	db.Model(&Dog{}).Where("id", 1).Find(&dog1)
	db.Model(&dog1).Association("Toy").Clear()
}

运行结果