gorm relationship one to one, one to many, many to many query

To achieve the function.
Article belongs to a category.
Articles have multiple labels

Four related tables Table in a database created in advance. No foreign key relationships

• article Table
• tag table.
• article_tag 表
• category table

//文章表
type Article struct {
  Id int `json:"id"`
  Title string `json:"title"`
  CategoryId int `json:"category_id"`
  Category Category `json:"category";gorm:"foreignkey:CategoryID"`//指定关联外键
  Tag []Tag `gorm:"many2many:article_tag" json:"tag"`//多对多关系.
  //article_tag表默认article_id字段对应article表id.tag_id字段对应tag表id
  //可以把对应sql日志打印出来,便于调试
}

//文章_标签中间表
type ArticleTag struct {
   Id int `json:"id" `
  ArticleId string `json:"article_id"`
  TagId string `json:"tag_id"`
  CreatedAt string `json:"created_at"`
  UpdatedAt string `json:"updated_at"`
}

//标签表
type Tag struct {
   Id int `json:"id" `
  TagName string `json:"tag_name"`
}

//分类表
type Category struct {
   ID int `json:"id"`
  CategoryName string `json:"category_name"`
  Status int `json:"status"`
  CreatedAt time.Time `json:"created_at"`
  UpdatedAt time.Time `json:"updated_at"`
}

//远程一对多.一对一
func (a *Article) ListArticle(title string) (Article, error) {
   query := database.GormPool
  var article Article
  query.Where("title like ?", "%"+title+"%").First(&article)
   fmt.Println(article)
   err := query.Model(&article).
      Related(&article.Category).
      Related(&article.Tag, "tag").
      Find(&article).Error
  if err != nil && err != gorm.ErrRecordNotFound {
      return article, nil
  }
   return article, err
}

The results are shown: a classification, a plurality of tags
used Related methods require good Article first query,
and then to find the definition of Category Article according to the CategoryID specified,
find a tag, label directly received Tag sections defined: Then write table corresponding to the gorm relationship: "many2many: article_tag"

func (a *Article) ListArticle(title string) (articles []Article, err error) {
	query := database.GormPool
	err = query.Model(articles).
		Where("title like ?", "%"+title+"%").
		Preload("Category").
		Preload("Tag").Find(&articles).Error
	if err != nil && err != gorm.ErrRecordNotFound {
		return
	}
	return
}

Preload method using direct mode as above will be able to find, as a result of the check out

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