在官网的实体关联底部有一个表格，讲的是关联标签

标签 描述
foreignKey 指定当前模型的列作为连接表的外键
references 指定引用表的列名，其将被映射为连接表外键
polymorphic 指定多态类型，比如模型名
polymorphicValue 指定多态值、默认表名
many2many 指定连接表表名
joinForeignKey 指定连接表的外键列名，其将被映射到当前表
joinReferences 指定连接表的外键列名，其将被映射到引用表
constraint 关系约束，例如：OnUpdate、OnDelete

关联标签可以自定义创建关联的时候，使用哪些列作为外键之类的（

其中有几个已经讲过了，然后最后一个一般不用，剩下的 4 个再挑出来讲一讲

foreignKey 与 references

还是用老师学生举例

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package main

type Info struct {
	Id    int
	Score int

	StudentID int
}

type Student struct {
	Id   int
	Name string
	Info Info

	TeacherID int
}

type Teacher struct {
	Id   int
	Name string

	// has many
	Student []Student
}

func hasMany() {
	GLOBAL_DB.AutoMigrate(&Student{}, &Teacher{}, &Info{})

	student1 := Student{Name: "student1"}
	student2 := Student{Name: "student2"}

	teacher1 := Teacher{
		Name: "teacher1",
		Student: []Student{
			student1,
			student2,
		},
	}

	GLOBAL_DB.Create(&teacher1)

}

image-20221009233002262

这里是用 TeacherID 作为外键，使用 foreignKey 与 references 标签指定其他的列为外键

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type Student struct {
	Id   int
	Name string
	Info Info

	TeacherName string
}

type Teacher struct {
	Id   int
	Name string

	// has many
	Student []Student `gorm:"foreignKey:TeacherName;references:Name"`
}

这个标签的意思是说：在其他模型中使用 TeacherName 作为外键，其值是本模型中的 Name

image-20221009234059913

joinForeignKey 与 joinReferences

上面的例子是在 has many 中，而在 many to many 中，如果要重写外键，最好加上这两个标签

  • joinForeignKey 指定关联表字段
  • joinReferences 指定关联表引用

其实就是手动指定关联表中的列名

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package main

type Student struct {
   Id          int
   StudentName string `gorm:"index:,unique"`

   // many2many
   Teachers []Teacher `gorm:"many2many:student_teachers;foreignkey:StudentName;joinForeignKey:student_name;references:TeacherName;joinreferences:teacher_name"`
}

type Teacher struct {
   Id          int
   TeacherName string `gorm:"index:,unique"`

   // many2many
   Students []Student `gorm:"many2many:student_teachers;foreignkey:TeacherName;joinForeignKey:teacher_name;references:StudentName;joinreferences:student_name"`
}

func many2many() {
   GLOBAL_DB.AutoMigrate(&Student{}, &Teacher{})

   teacher1 := Teacher{TeacherName: "teacher1"}
   teacher2 := Teacher{TeacherName: "teacher2"}
   student1 := Student{
      StudentName: "student1",
      Teachers:    []Teacher{teacher1, teacher2},
   }
   GLOBAL_DB.Create(&student1)

   //var student = Student{Id: 1}
   //var result []Teacher
   //GLOBAL_DB.Model(&student).Preload("Students").Association("Teachers").Find(&result)
   //fmt.Println(result)
}

image-20221010091433814