gorm将查询结果映射到自定义嵌套结构体，嵌套预加载

type Project struct {
	Id              int64     `form:"-"`
	Code            string    `orm:"null"`                                              //编号
	Title           string    `form:"title;text;title:",valid:"MinSize(1);MaxSize(20)"` //orm:"unique",
	Label           string    `orm:"null"`                                              //标签
	Principal       string    `orm:"null"`                                              //负责人id
	ParentId        int64     `orm:"null"`
	ParentIdPath    string    `orm:"null"`
	ParentTitlePath string    `orm:"null"`
	Grade           int       `orm:"null"`
	Created         time.Time `orm:"null","auto_now_add;type(datetime)"`
	Updated         time.Time `orm:"null","auto_now_add;type(datetime)"`
}

//用户-历史计算记录表
type UserHistory struct {
	gorm.Model
	// ID     int    `gorm:"primary_key"`
	UserID       int64 `json:"userid" gorm:"column:user_id;"`
	UserTempleID uint  `json:"tempid" gorm:"column:user_temple_id"`
	User         User  `gorm:"foreignkey:Id;references:UserID;"`
	UserTemple   UserTemple
	PdfUrl       string `json:"pdfurl"`
	FaceImgUrl   string `json:"faceimgurl"`
	Description  string `json:"description"`
}

type PassProject struct {
	gorm.Model
	UserHistoryID uint        `json:"historyid" gorm:"column:history_id;`
	ProjectId     int64       `json:"projectid" gorm:"column:project_id;`
	Userhistory   UserHistory `json:"userhistory" gorm:"foreignKey:ID;references:UserHistoryID;"` //ID是UserHistory结构中的，UserHistoryID是本表中的
}

// 专业——典型的一对多关联和自定义结构体
type UserProfession struct {
	// gorm.Model
	Id int64
	// ProjectId int64
	Title string `json:"profession_title"` //阶段名称
	// UserHistoryID uint
	PassProjects []PassProject `gorm:"foreignKey:ProjectId;references:Id;"` //ProjectId是PassProject数据结构中的，Id是本表中的
}

// 典型的将查询结果映射到自定义结构体，利用了预加载和一对多关联、嵌套预加载
func GetProjectMathHis(projectid int64) (userprofession []UserProfession, err error) {
	db := _db
	err = db.Table("project"). //Order("project.updated desc"). //Order("pass_projects.userhistory.updated_at desc").
					Preload("PassProjects").
					Preload("PassProjects.Userhistory"). //嵌套预加载
					Where("project.parent_id = ?", projectid).
					Find(&userprofession).Error
	return userprofession, err
}