作用域允许你复用通用的逻辑，这种共享逻辑需要定义为类型func(*gorm.DB) *gorm.DB。

查询

Scope 查询示例：

  1. func AmountGreaterThan1000(db *gorm.DB) *gorm.DB {
  2.   return db.Where("amount > ?", 1000)
  3. }
  5. func PaidWithCreditCard(db *gorm.DB) *gorm.DB {
  6.   return db.Where("pay_mode_sign = ?", "C")
  7. }
  9. func PaidWithCod(db *gorm.DB) *gorm.DB {
  10.   return db.Where("pay_mode_sign = ?", "C")
  11. }
  13. func OrderStatus(status []string) func (db *gorm.DB) *gorm.DB {
  14.   return func (db *gorm.DB) *gorm.DB {
  15.     return db.Where("status IN (?)", status)
  16.   }
  17. }
  19. db.Scopes(AmountGreaterThan1000, PaidWithCreditCard).Find(&orders)
  20. // 查找所有金额大于 1000 的信用卡订单
  22. db.Scopes(AmountGreaterThan1000, PaidWithCod).Find(&orders)
  23. // 查找所有金额大于 1000 的 COD 订单
  25. db.Scopes(AmountGreaterThan1000, OrderStatus([]string{"paid", "shipped"})).Find(&orders)
  26. // 查找所有金额大于1000 的已付款或已发货订单

分页

  1. func Paginate(r *http.Request) func(db *gorm.DB) *gorm.DB {
  2.   return func (db *gorm.DB) *gorm.DB {
  3.     q := r.URL.Query()
  4.     page, _ := strconv.Atoi(q.Get("page"))
  5.     if page <= 0 {
  6.       page = 1
  7.     }
  9.     pageSize, _ := strconv.Atoi(q.Get("page_size"))
  10.     switch {
  11.     case pageSize > 100:
  12.       pageSize = 100
  13.     case pageSize <= 0:
  14.       pageSize = 10
  15.     }
  17.     offset := (page - 1) * pageSize
  18.     return db.Offset(offset).Limit(pageSize)
  19.   }
  20. }
  22. db.Scopes(Paginate(r)).Find(&users)
  23. db.Scopes(Paginate(r)).Find(&articles)

动态表

使用 Scopes 来动态指定查询的表

  1. func TableOfYear(user *User, year int) func(db *gorm.DB) *gorm.DB {
  2.   return func(db *gorm.DB) *gorm.DB {
  3.         tableName := user.TableName() + strconv.Itoa(year)
  4.         return db.Table(tableName)
  5.   }
  6. }
  8. DB.Scopes(TableOfYear(user, 2019)).Find(&users)
  9. // SELECT * FROM users_2019;
  11. DB.Scopes(TableOfYear(user, 2020)).Find(&users)
  12. // SELECT * FROM users_2020;
  14. // Table form different database
  15. func TableOfOrg(user *User, dbName string) func(db *gorm.DB) *gorm.DB {
  16.   return func(db *gorm.DB) *gorm.DB {
  17.         tableName := dbName + "." + user.TableName()
  18.         return db.Table(tableName)
  19.   }
  20. }
  22. DB.Scopes(TableOfOrg(user, "org1")).Find(&users)
  23. // SELECT * FROM org1.users;
  25. DB.Scopes(TableOfOrg(user, "org2")).Find(&users)
  26. // SELECT * FROM org2.users;

更新

Scope 更新、删除示例：

  1. func CurOrganization(r *http.Request) func(db *gorm.DB) *gorm.DB {
  2.   return func (db *gorm.DB) *gorm.DB {
  3.     org := r.Query("org")
  5.     if org != "" {
  6.       var organization Organization
  7.       if db.Session(&Session{}).First(&organization, "name = ?", org).Error == nil {
  8.         return db.Where("org_id = ?", organization.ID)
  9.       }
  10.     }
  12.     db.AddError("invalid organization")
  13.     return db
  14.   }
  15. }
  17. db.Model(&article).Scopes(CurOrganization(r)).Update("Name", "name 1")
  18. // UPDATE articles SET name = "name 1" WHERE org_id = 111
  19. db.Scopes(CurOrganization(r)).Delete(&Article{})
  20. // DELETE FROM articles WHERE org_id = 111