Gorm入门，带你实现简单的增删改查|青训营

3、改[Update]

更新指定记录

//-----------------------------保存所有字段-------------------------
db.First(&user)
user.Name = "jinzhu 2"
user.Age = 100
db.Save(&user)
// UPDATE users SET name='jinzhu 2', age=100, birthday='2016-01-01', updated_at = '2013-11-17 21:34:10' WHERE id=111;

//-----------------------------更新单个列-------------------------
// 条件更新
db.Model(&User{}).Where("active = ?", true).Update("name", "hello")
// UPDATE users SET name='hello', updated_at='2013-11-17 21:34:10' WHERE active=true;

// User 的 ID 是 `111`
db.Model(&user).Update("name", "hello")
// UPDATE users SET name='hello', updated_at='2013-11-17 21:34:10' WHERE id=111;

// 根据条件和 model 的值进行更新
db.Model(&user).Where("active = ?", true).Update("name", "hello")
// UPDATE users SET name='hello', updated_at='2013-11-17 21:34:10' WHERE id=111 AND active=true;

//-----------------------------更新多列-------------------------
// 根据 `struct` 更新属性，只会更新非零值的字段
db.Model(&user).Updates(User{Name: "hello", Age: 18, Active: false})
// UPDATE users SET name='hello', age=18, updated_at = '2013-11-17 21:34:10' WHERE id = 111;

// 根据 `map` 更新属性
db.Model(&user).Updates(map[string]interface{}{"name": "hello", "age": 18, "active": false})
// UPDATE users SET name='hello', age=18, active=false, updated_at='2013-11-17 21:34:10' WHERE id=111;

//-----------------------------更新选定字段-------------------------
// 使用 Map 进行 Select
// User's ID is `111`:
db.Model(&user).Select("name").Updates(map[string]interface{}{"name": "hello", "age": 18, "active": false})
// UPDATE users SET name='hello' WHERE id=111;

db.Model(&user).Omit("name").Updates(map[string]interface{}{"name": "hello", "age": 18, "active": false})
// UPDATE users SET age=18, active=false, updated_at='2013-11-17 21:34:10' WHERE id=111;

// 使用 Struct 进行 Select（会 select 零值的字段）
db.Model(&user).Select("Name", "Age").Updates(User{Name: "new_name", Age: 0})
// UPDATE users SET name='new_name', age=0 WHERE id=111;

// Select 所有字段（查询包括零值字段的所有字段）
db.Model(&user).Select("*").Update(User{Name: "jinzhu", Role: "admin", Age: 0})

// Select 除 Role 外的所有字段（包括零值字段的所有字段）
db.Model(&user).Select("*").Omit("Role").Update(User{Name: "jinzhu", Role: "admin", Age: 0})

更新批量记录

//-----------------------------批量更新-------------------------
// 根据 struct 更新
db.Model(User{}).Where("role = ?", "admin").Updates(User{Name: "hello", Age: 18})
// UPDATE users SET name='hello', age=18 WHERE role = 'admin';

// 根据 map 更新
db.Table("users").Where("id IN ?", []int{10, 11}).Updates(map[string]interface{}{"name": "hello", "age": 18})
// UPDATE users SET name='hello', age=18 WHERE id IN (10, 11);

//-----------------------------禁止全局更新-------------------------
//如果在没有任何条件的情况下执行批量更新，默认情况下，GORM 不会执行该操作，并返回 ErrMissingWhereClause 错误。对此，必须加一些条件，或者使用原生 SQL，或者启用 AllowGlobalUpdate 模式
db.Model(&User{}).Update("name", "jinzhu").Error // gorm.ErrMissingWhereClause

db.Model(&User{}).Where("1 = 1").Update("name", "jinzhu")
// UPDATE users SET `name` = "jinzhu" WHERE 1=1

db.Exec("UPDATE users SET name = ?", "jinzhu")
// UPDATE users SET name = "jinzhu"

db.Session(&gorm.Session{AllowGlobalUpdate: true}).Model(&User{}).Update("name", "jinzhu")
// UPDATE users SET `name` = "jinzhu"

//-----------------------------更新记录数-------------------------
// 通过 `RowsAffected` 得到更新的记录数
result := db.Model(User{}).Where("role = ?", "admin").Updates(User{Name: "hello", Age: 18})
// UPDATE users SET name='hello', age=18 WHERE role = 'admin';

result.RowsAffected // 更新的记录数
result.Error        // 更新的错误

更新hook【更新钩子】

//-----------------------------更新 Hook-------------------------
//GORM 支持 BeforeSave、BeforeUpdate、AfterSave、AfterUpdate 钩子，这些方法将在更新记录时被调用
func (u *User) BeforeUpdate(tx *gorm.DB) (err error) {
    if u.Role == "admin" {
        return errors.New("admin user not allowed to update")
    }
    return
}

4、删[Delete]

删除指定记录

//-----------------------------删除一条记录-------------------------
//删除一条记录时，删除对象需要指定主键，否则会触发 批量 Delete
// Email 的 ID 是 `10`
db.Delete(&email)
// DELETE from emails where id = 10;

// 带额外条件的删除
db.Where("name = ?", "jinzhu").Delete(&email)
// DELETE from emails where id = 10 AND name = "jinzhu";

//-----------------------------根据主键删除-------------------------
db.Delete(&User{}, 10)
// DELETE FROM users WHERE id = 10;

db.Delete(&User{}, "10")
// DELETE FROM users WHERE id = 10;

db.Delete(&users, []int{1,2,3})
// DELETE FROM users WHERE id IN (1,2,3);

删除批量记录

//-----------------------------批量删除-------------------------
db.Where("email LIKE ?", "%jinzhu%").Delete(&Email{})
// DELETE from emails where email LIKE "%jinzhu%";

db.Delete(&Email{}, "email LIKE ?", "%jinzhu%")
// DELETE from emails where email LIKE "%jinzhu%";

//-----------------------------禁止全局删除-------------------------
//如果在没有任何条件的情况下执行批量删除，GORM 不会执行该操作，并返回 ErrMissingWhereClause 错误。对此，你必须加一些条件，或者使用原生 SQL，或者启用 AllowGlobalUpdate 模式
db.Delete(&User{}).Error // gorm.ErrMissingWhereClause

db.Where("1 = 1").Delete(&User{})
// DELETE FROM `users` WHERE 1=1

db.Exec("DELETE FROM users")
// DELETE FROM users

db.Session(&gorm.Session{AllowGlobalUpdate: true}).Delete(&User{})
// DELETE FROM users

软删除【重点】

如果model包含gorm.deleted_at 字段（gorm.Model 已经包含了该字段)，它将自动获得软删除的能力！拥有软删除能力的模型调用 Delete 时，记录不会从数据库中被真正删除。GORM 会将 DeletedAt 置为当前时间，并且不能再通过普通的查询方法找到该记录。

//-----------------------------软删除-------------------------
//By default, gorm.Model uses *time.Time as the value for the DeletedAt field, and it provides other data formats support with plugin gorm.io/plugin/soft_delete
import "gorm.io/plugin/soft_delete"
type User struct {
  ID        uint
  Name      string                `gorm:"uniqueIndex:udx_name"`
  DeletedAt soft_delete.DeletedAt `gorm:"uniqueIndex:udx_name"`
  // DeletedAt soft_delete.DeletedAt `gorm:"softDelete:nano"`
  //IsDel soft_delete.DeletedAt `gorm:"softDelete:flag"`
}

// Query
SELECT * FROM users WHERE is_del = 0;

// Delete
UPDATE users SET is_del = 1 WHERE ID = 1;

// user 的 ID 是 `111`
db.Delete(&user)
// UPDATE users SET deleted_at="2013-10-29 10:23" WHERE id = 111;

// 批量删除
db.Where("age = ?", 20).Delete(&User{})
// UPDATE users SET deleted_at="2013-10-29 10:23" WHERE age = 20;

// 在查询时会忽略被软删除的记录
db.Where("age = 20").Find(&user)
// SELECT * FROM users WHERE age = 20 AND deleted_at IS NULL;

//-----------------------------查找被软删除的记录-------------------------
db.Unscoped().Where("age = 20").Find(&users)
// SELECT * FROM users WHERE age = 20;

//-----------------------------永久删除-------------------------
db.Unscoped().Delete(&order)
// DELETE FROM orders WHERE id=10;

删除hook【删除钩子】

//-----------------------------删除 Hook-------------------------
func (u *User) BeforeDelete(tx *gorm.DB) (err error) {
    if u.Role == "admin" {
        return errors.New("admin user not allowed to delete")
    }
    return
}

原生sql

如果你非常熟悉sql语句，并且需要灵活度较高的sql操作，可以使用Gorm支持的原生sql操作来对数据库进行操作

//-----------------------------原生查询 SQL 和 Scan-------------------------
type Result struct {
  ID   int
  Name string
  Age  int
}

var result Result
db.Raw("SELECT id, name, age FROM users WHERE name = ?", 3).Scan(&result)

db.Raw("SELECT id, name, age FROM users WHERE name = ?", 3).Scan(&result)

var age int
db.Raw("SELECT SUM(age) FROM users WHERE role = ?", "admin").Scan(&age)

var users []User
db.Raw("UPDATE users SET name = ? WHERE age = ? RETURNING id, name", "jinzhu", 20).Scan(&users)

原生 Exec SQL

//-----------------------------Exec 原生 SQL-------------------------
db.Exec("DROP TABLE users")
db.Exec("UPDATE orders SET shipped_at = ? WHERE id IN ?", time.Now(), []int64{1, 2, 3})

// Exec with SQL Expression
db.Exec("UPDATE users SET money = ? WHERE name = ?", gorm.Expr("money * ? + ?", 10000, 1), "jinzhu")

Row和Rows

//获取 *sql.Row 结果
// 使用 GORM API 构建 SQL
row := db.Table("users").Where("name = ?", "jinzhu").Select("name", "age").Row()
row.Scan(&name, &age)

// 使用原生 SQL
row := db.Raw("select name, age, email from users where name = ?", "jinzhu").Row()
row.Scan(&name, &age, &email)

// 原生 SQL
rows, err := db.Raw("select name, age, email from users where name = ?", "jinzhu").Rows()
defer rows.Close()
for rows.Next() {
  rows.Scan(&name, &age, &email)
  // 业务逻辑...
}

rows, err := db.Model(&User{}).Where("name = ?", "jinzhu").Select("name, age, email").Rows() // (*sql.Rows, error)
defer rows.Close()

var user User
for rows.Next() {
  // ScanRows 将一行扫描至 user
  db.ScanRows(rows, &user)
  // 业务逻辑...
}