有一个student表:

他与lesson表:

根据lessonstudent表关联：

他们仨的关联关系如图所示：

初始化表

//lesson.go
type Lesson struct {
	Id      int
	Name    string
	Student []Student `gorm:"many2many:lesson_student;"` //many-to-many
}

func (Lesson) TableName() string {
	return "lesson"
}

//lessonStudent.go
type LessonStudent struct {
	LessonId  int
	StudentId int
}

func (LessonStudent) TableName() string {
	return "lesson_student"
}
//student.go
type Student struct {
	Id       int
	Number   string
	Password string
	ClassId  int
	Name     string
	//Lesson   []Lesson `gorm:"many2many:lesson_student;"`
}

func (Student) TableName() string {
	return "student"
}


//controller.go
type StudentController struct {
	BaseController
}

1、查询student信息时获取lesson课信息

func (con StudentController) Index(c *gin.Context) {
	stuList := []models.Student{}
	//查询学生信息时获取学生选修课信息
	models.DB.Preload("Lesson").Find(&stuList)
	c.JSON(http.StatusOK, gin.H{
		"result": stuList,
	})
}

func (con StudentController) Detail(c *gin.Context) {
	//查询张三信息时获取张三选修课信息
	stuList := []models.Student{}
	models.DB.Preload("Lesson").Where("Name = ?", "张三").Find(&stuList)
	c.JSON(http.StatusOK, gin.H{
		"result": stuList,
	})
}

2、查询lesson被哪些student选修了

func (con StudentController) LessonByStu(c *gin.Context) {
	lessonList := []models.Lesson{}
	//查询课程被哪些学生选修了
	//models.DB.Preload("Student").Find(&lessonList)

	//查询课程被哪些学生选修了（id倒叙）
	models.DB.Preload("Student", func(db *gorm.DB) *gorm.DB { return db.Order("student.id desc") }).Find(&lessonList)
	c.JSON(http.StatusOK, gin.H{
		"result": lessonList,
	})
}

3、去掉某一个student信息的lesson

func (con StudentController) LessonExcept(c *gin.Context) {
	//张三被开除了，查询课程被哪些学生选修了（去掉张三）
	lessonList := []models.Lesson{}
	models.DB.Preload("Student", "id !=?", 1).Find(&lessonList)
	c.JSON(http.StatusOK, gin.H{
		"result": lessonList,
	})
}