创建
创建记录
首先定义模型：
type User struct {
ID int64
Name string
Age int64
}
使用使用NewRecord()查询主键是否存在，主键为空使用Create()创建记录：
user := User{
Name: "zhurunhua", Age: 18}
db.NewRecord(user) // 主键为空返回`true`
db.Create(&user) // 创建user
db.NewRecord(user) // 创建`user`后返回`false`
默认值
可以通过 tag 定义字段的默认值，比如：
type User struct {
ID int64
Name string `gorm:"default:'zhurunhua'"`
Age int64
}
**注意：**通过tag定义字段的默认值，在创建记录时候生成的 SQL 语句会排除没有值或值为 零值 的字段。 在将记录插入到数据库后，Gorm会从数据库加载那些字段的默认值。
举个例子：
var user = User{
Name: "", Age: 99}
db.Create(&user)
上面代码实际执行的SQL语句是INSERT INTO users("age") values('99');，排除了零值字段Name，而在数据库中这一条数据会使用设置的默认值zhurunhua作为Name字段的值。
**注意：**所有字段的零值, 比如0, "",false或者其它零值，都不会保存到数据库内，但会使用他们的默认值。 如果你想避免这种情况，可以考虑使用指针或实现 Scanner/Valuer接口，比如：
使用指针方式实现零值存入数据库
// 使用指针
type User struct {
ID int64
Name *string `gorm:"default:'zhurunhua'"`
Age int64
}
user := User{
Name: new(string), Age: 18))}
db.Create(&user) // 此时数据库中该条记录name字段的值就是''
使用Scanner/Valuer接口方式实现零值存入数据库
// 使用 Scanner/Valuer
type User struct {
ID int64
Name sql.NullString `gorm:"default:'zhurunhua'"` // sql.NullString 实现了Scanner/Valuer接口
Age int64
}
user := User{
Name: sql.NullString{
"", true}, Age:18}
db.Create(&user) // 此时数据库中该条记录name字段的值就是''
扩展创建选项
例如PostgreSQL数据库中可以使用下面的方式实现合并插入, 有则更新, 无则插入。
// 为Instert语句添加扩展SQL选项
db.Set("gorm:insert_option", "ON CONFLICT").Create(&product)
// INSERT INTO products (name, code) VALUES ("name", "code") ON CONFLICT;
// 创建表时添加表后缀
db.Set("gorm:table_options", "ENGINE=InnoDB").AutoMigrate(&User{
})
钩子方法
钩子是在创建、查询、更新、删除等操作之前、之后调用的函数。
如果您已经为模型定义了指定的方法，它会在创建、更新、查询、删除时自动被调用。如果任何回调返回错误，GORM 将停止后续的操作并回滚事务。
func (s Student) BeforeCreate(tx *gorm.DB) (err error) {
if len(s.StudentNum) > 16 {
return errors.New("学号非法")
}
fmt.Println("学号校验通过")
return nil
}
func (s Student) AfterCreate(tx *gorm.DB) (err error) {
fmt.Printf("学员：【%s】档案已创建！", s.StudentName)
return
}
func (s Student) AfterSave(tx *gorm.DB) (err error) {
fmt.Printf("学员：【%s】档案已保存！", s.StudentName)
return
}
//如果要对查询出来的数据修改，使用指针类型
func (s *Student) AfterFind(tx *gorm.DB) (err error) {
if s.Gender == 1 {
s.GenderName = "男"
} else if s.Gender == 2 {
s.GenderName = "女"
}
return
}
Upsert 及冲突
GORM 为不同数据库提供了兼容的 Upsert 支持
student := &entity.Student{
StudentNum: "10001",
StudentName: "李逍遥",
Gender: 1,
Birthday: "1900-01-02",
//以下两种方式解决零值问题
//Address: new(string),
//Address: sql.NullString{"", true},
}
//忽略冲突，创建不成功，也不报错
db.Debug().Clauses(clause.OnConflict{
DoNothing: true}).Create(student)
/**
在student_num冲突时，将name列更新为新值
INSERT INTO `students` ( `student_num`, `name`, `gender`, `birthday`, `address`, `created_at`, `updated_at`, `deleted_at` )
VALUES
( '2', '李逍遥', 1, '1900-01-02', '蜀山', '2021-11-04 19:57:43.356', '2021-11-04 19:57:43.356', NULL )
ON DUPLICATE KEY UPDATE `name` =
VALUES
( `name` )
*/
db.Debug().Clauses(clause.OnConflict{
Columns: []clause.Column{
{
Name: "student_num"}},
DoUpdates: clause.AssignmentColumns([]string{
"name"}),
}).Create(getStudent())
查询
一般查询
// 根据主键查询第一条记录
db.First(&user)
SELECT * FROM users ORDER BY id LIMIT 1;
// 获取一条记录（不指定排序字段）
db.Take(&user)
SELECT * FROM users LIMIT 1;
// 根据主键查询最后一条记录
db.Last(&user)
SELECT * FROM users ORDER BY id DESC LIMIT 1;
// 查询所有的记录
db.Find(&users)
SELECT * FROM users;
// 查询指定的某条记录(仅当主键为整型时可用)
db.First(&user, 10)
SELECT * FROM users WHERE id = 10;
Where 条件
普通SQL查询
// Get first matched record
db.Where("name = ?", "lixiaoyao").First(&user)
SELECT * FROM users WHERE name = 'lixiaoyao' limit 1;
// Get all matched records
db.Where("name = ?", "lixiaoyao").Find(&users)
SELECT * FROM users WHERE name = 'lixiaoyao';
// <>
db.Where("name <> ?", "lixiaoyao").Find(&users)
SELECT * FROM users WHERE name <> 'lixiaoyao';
// IN
db.Where("name IN (?)", []string{
"lixiaoyao", "lixiaoyao 2"}).Find(&users)
SELECT * FROM users WHERE name in ('lixiaoyao','lixiaoyao 2');
// LIKE
db.Where("name LIKE ?", "%jin%").Find(&users)
SELECT * FROM users WHERE name LIKE '%jin%';
// AND
db.Where("name = ? AND age >= ?", "lixiaoyao", "22").Find(&users)
SELECT * FROM users WHERE name = 'lixiaoyao' AND age >= 22;
// Time
db.Where("updated_at > ?", lastWeek).Find(&users)
SELECT * FROM users WHERE updated_at > '2000-01-01 00:00:00';
// BETWEEN
db.Where("created_at BETWEEN ? AND ?", lastWeek, today).Find(&users)
SELECT * FROM users WHERE created_at BETWEEN '2000-01-01 00:00:00' AND '2000-01-08 00:00:00';
Struct & Map查询
// Struct
db.Where(&User{
Name: "lixiaoyao", Age: 20}).First(&user)
SELECT * FROM users WHERE name = "lixiaoyao" AND age = 20 LIMIT 1;
// Map
db.Where(map[string]interface{
}{
"name": "lixiaoyao", "age": 20}).Find(&users)
SELECT * FROM users WHERE name = "lixiaoyao" AND age = 20;
// 主键的切片
db.Where([]int64{
20, 21, 22}).Find(&users)
SELECT * FROM users WHERE id IN (20, 21, 22);
**提示：**当通过结构体进行查询时，GORM将会只通过非零值字段查询，这意味着如果你的字段值为0，''，false或者其他零值时，将不会被用于构建查询条件，例如：
db.Where(&User{
Name: "lixiaoyao", Age: 0}).Find(&users)
SELECT * FROM users WHERE name = "lixiaoyao";
你可以使用指针或实现 Scanner/Valuer 接口来避免这个问题.
// 使用指针
type User struct {
gorm.Model
Name string
Age *int
}
// 使用 Scanner/Valuer
type User struct {
gorm.Model
Name string
Age sql.NullInt64 // sql.NullInt64 实现了 Scanner/Valuer 接口
}
Not 条件
作用与 Where 类似的情形如下：
db.Not("name", "lixiaoyao").First(&user)
SELECT * FROM users WHERE name <> "lixiaoyao" LIMIT 1;
// Not In
db.Not("name", []string{
"lixiaoyao", "lixiaoyao 2"}).Find(&users)
SELECT * FROM users WHERE name NOT IN ("lixiaoyao", "lixiaoyao 2");
// Not In slice of primary keys
db.Not([]int64{
1,2,3}).First(&user)
SELECT * FROM users WHERE id NOT IN (1,2,3);
db.Not([]int64{
}).First(&user)
SELECT * FROM users;
// Plain SQL
db.Not("name = ?", "lixiaoyao").First(&user)
SELECT * FROM users WHERE NOT(name = "lixiaoyao");
// Struct
db.Not(User{
Name: "lixiaoyao"}).First(&user)
SELECT * FROM users WHERE name <> "lixiaoyao";
Or条件
db.Where("role = ?", "admin").Or("role = ?", "super_admin").Find(&users)
SELECT * FROM users WHERE role = 'admin' OR role = 'super_admin';
// Struct
db.Where("name = 'lixiaoyao'").Or(User{
Name: "lixiaoyao 2"}).Find(&users)
SELECT * FROM users WHERE name = 'lixiaoyao' OR name = 'lixiaoyao 2';
// Map
db.Where("name = 'lixiaoyao'").Or(map[string]interface{
}{
"name": "lixiaoyao 2"}).Find(&users)
SELECT * FROM users WHERE name = 'lixiaoyao' OR name = 'lixiaoyao 2';
内联条件
作用与Where查询类似，当内联条件与多个立即执行方法一起使用时, 内联条件不会传递给后面的立即执行方法。
// 根据主键获取记录 (只适用于整形主键)
db.First(&user, 23)
SELECT * FROM users WHERE id = 23 LIMIT 1;
// 根据主键获取记录, 如果它是一个非整形主键
db.First(&user, "id = ?", "string_primary_key")
SELECT * FROM users WHERE id = 'string_primary_key' LIMIT 1;
db.Find(&user, "name = ?", "lixiaoyao")
SELECT * FROM users WHERE name = "lixiaoyao";
db.Find(&users, "name <> ? AND age > ?", "lixiaoyao", 20)
SELECT * FROM users WHERE name <> "lixiaoyao" AND age > 20;
// Struct
db.Find(&users, User{
Age: 20})
SELECT * FROM users WHERE age = 20;
// Map
db.Find(&users, map[string]interface{
}{
"age": 20})
SELECT * FROM users WHERE age = 20;
额外查询选项
// 为查询 SQL 添加额外的 SQL 操作
db.Set("gorm:query_option", "FOR UPDATE").First(&user, 10)
SELECT * FROM users WHERE id = 10 FOR UPDATE;
FirstOrInit
获取匹配的第一条记录，否则根据给定的条件初始化一个新的对象 (仅支持 struct 和 map 条件)
// 未找到
db.FirstOrInit(&user, User{
Name: "non_existing"})
user -> User{Name: "non_existing"}
// 找到
db.Where(User{
Name: "lixiaoyao"}).FirstOrInit(&user)
user -> User{Id: 111, Name: "lixiaoyao", Age: 20}
db.FirstOrInit(&user, map[string]interface{
}{
"name": "lixiaoyao"})
user -> User{Id: 111, Name: "lixiaoyao", Age: 20}
Attrs
如果记录未找到，将使用参数初始化 struct.
// 未找到
db.Where(User{
Name: "non_existing"}).Attrs(User{
Age: 20}).FirstOrInit(&user)
SELECT * FROM USERS WHERE name = 'non_existing';
user -> User{Name: "non_existing", Age: 20}
db.Where(User{
Name: "non_existing"}).Attrs("age", 20).FirstOrInit(&user)
SELECT * FROM USERS WHERE name = 'non_existing';
user -> User{Name: "non_existing", Age: 20}
// 找到
db.Where(User{
Name: "lixiaoyao"}).Attrs(User{
Age: 30}).FirstOrInit(&user)
SELECT * FROM USERS WHERE name = lixiaoyao';
user -> User{Id: 111, Name: "lixiaoyao", Age: 20}
Assign
不管记录是否找到，都将参数赋值给 struct.
// 未找到
db.Where(User{
Name: "non_existing"}).Assign(User{
Age: 20}).FirstOrInit(&user)
user -> User{Name: "non_existing", Age: 20}
// 找到
db.Where(User{
Name: "lixiaoyao"}).Assign(User{
Age: 30}).FirstOrInit(&user)
SELECT * FROM USERS WHERE name = lixiaoyao';
user -> User{Id: 111, Name: "lixiaoyao", Age: 30}
FirstOrCreate
获取匹配的第一条记录, 否则根据给定的条件创建一个新的记录 (仅支持 struct 和 map 条件)
// 未找到
db.FirstOrCreate(&user, User{
Name: "non_existing"})
INSERT INTO "users" (name) VALUES ("non_existing");
user -> User{Id: 112, Name: "non_existing"}
// 找到
db.Where(User{
Name: "lixiaoyao"}).FirstOrCreate(&user)
user -> User{Id: 111, Name: "lixiaoyao"}
Attrs
如果记录未找到，将使用参数创建 struct 和记录.
// 未找到
db.Where(User{
Name: "non_existing"}).Attrs(User{
Age: 20}).FirstOrCreate(&user)
SELECT * FROM users WHERE name = 'non_existing';
INSERT INTO "users" (name, age) VALUES ("non_existing", 20);
user -> User{Id: 112, Name: "non_existing", Age: 20}
// 找到
db.Where(User{
Name: "lixiaoyao"}).Attrs(User{
Age: 30}).FirstOrCreate(&user)
SELECT * FROM users WHERE name = 'lixiaoyao';
user -> User{Id: 111, Name: "lixiaoyao", Age: 20}
Assign
不管记录是否找到，都将参数赋值给 struct 并保存至数据库.
// 未找到
db.Where(User{
Name: "non_existing"}).Assign(User{
Age: 20}).FirstOrCreate(&user)
SELECT * FROM users WHERE name = 'non_existing';
INSERT INTO "users" (name, age) VALUES ("non_existing", 20);
user -> User{Id: 112, Name: "non_existing", Age: 20}
// 找到
db.Where(User{
Name: "lixiaoyao"}).Assign(User{
Age: 30}).FirstOrCreate(&user)
SELECT * FROM users WHERE name = 'lixiaoyao';
UPDATE users SET age=30 WHERE id = 111;
user -> User{Id: 111, Name: "lixiaoyao", Age: 30}
高级查询
子查询
子查询可以嵌套在查询中，GORM 允许在使用 *gorm.DB 对象作为参数时生成子查询
db.Where("amount > ?", db.Table("orders").Select("AVG(amount)")).Find(&orders)
// SELECT * FROM "orders" WHERE amount > (SELECT AVG(amount) FROM "orders");
subQuery := db.Select("AVG(age)").Where("name LIKE ?", "name%").Table("users")
db.Select("AVG(age) as avgage").Group("name").Having("AVG(age) > (?)", subQuery).Find(&results)
// SELECT AVG(age) as avgage FROM `users` GROUP BY `name` HAVING AVG(age) > (SELECT AVG(age) FROM `users` WHERE name LIKE "name%")
选择字段
Select，指定你想从数据库中检索出的字段，默认会选择全部字段。
db.Select("name, age").Find(&users)
SELECT name, age FROM users;
db.Select([]string{
"name", "age"}).Find(&users)
SELECT name, age FROM users;
db.Table("users").Select("COALESCE(age,?)", 42).Rows()
SELECT COALESCE(age,'42') FROM users;
排序
Order，指定从数据库中检索出记录的顺序。设置第二个参数 reorder 为 true ，可以覆盖前面定义的排序条件。
db.Order("age desc, name").Find(&users)
SELECT * FROM users ORDER BY age desc, name;
// 多字段排序
db.Order("age desc").Order("name").Find(&users)
SELECT * FROM users ORDER BY age desc, name;
// 覆盖排序
db.Order("age desc").Find(&users1).Order("age", true).Find(&users2)
SELECT * FROM users ORDER BY age desc; (users1)
SELECT * FROM users ORDER BY age; (users2)
数量
Limit，指定从数据库检索出的最大记录数。
db.Limit(3).Find(&users)
SELECT * FROM users LIMIT 3;
// -1 取消 Limit 条件
db.Limit(10).Find(&users1).Limit(-1).Find(&users2)
SELECT * FROM users LIMIT 10; (users1)
SELECT * FROM users; (users2)
偏移
Offset，指定开始返回记录前要跳过的记录数。
db.Offset(3).Find(&users)
SELECT * FROM users OFFSET 3;
// -1 取消 Offset 条件
db.Offset(10).Find(&users1).Offset(-1).Find(&users2)
SELECT * FROM users OFFSET 10; (users1)
SELECT * FROM users; (users2)
总数
Count，该 model 能获取的记录总数。
db.Where("name = ?", "lixiaoyao").Or("name = ?", "lixiaoyao 2").Find(&users).Count(&count)
SELECT * from USERS WHERE name = 'lixiaoyao' OR name = 'lixiaoyao 2'; (users)
SELECT count(*) FROM users WHERE name = 'lixiaoyao' OR name = 'lixiaoyao 2'; (count)
db.Model(&User{
}).Where("name = ?", "lixiaoyao").Count(&count)
SELECT count(*) FROM users WHERE name = 'lixiaoyao'; (count)
db.Table("deleted_users").Count(&count)
SELECT count(*) FROM deleted_users;
db.Table("deleted_users").Select("count(distinct(name))").Count(&count)
SELECT count( distinct(name) ) FROM deleted_users; (count)
注意 Count 必须是链式查询的最后一个操作 ，因为它会覆盖前面的 SELECT，但如果里面使用了 count 时不会覆盖
Group & Having
rows, err := db.Table("orders").Select("date(created_at) as date, sum(amount) as total").Group("date(created_at)").Rows()
for rows.Next() {
...
}
// 使用Scan将多条结果扫描进事先准备好的结构体切片中
type Result struct {
Date time.Time
Total int
}
var rets []Result
db.Table("users").Select("date(created_at) as date, sum(age) as total").Group("date(created_at)").Scan(&rets)
rows, err := db.Table("orders").Select("date(created_at) as date, sum(amount) as total").Group("date(created_at)").Having("sum(amount) > ?", 100).Rows()
for rows.Next() {
...
}
type Result struct {
Date time.Time
Total int64
}
db.Table("orders").Select("date(created_at) as date, sum(amount) as total").Group("date(created_at)").Having("sum(amount) > ?", 100).Scan(&results)
连接
Joins，指定连接条件
rows, err := db.Table("users").Select("users.name, emails.email").Joins("left join emails on emails.user_id = users.id").Rows()
for rows.Next() {
...
}
db.Table("users").Select("users.name, emails.email").Joins("left join emails on emails.user_id = users.id").Scan(&results)
// 多连接及参数
db.Joins("JOIN emails ON emails.user_id = users.id AND emails.email = ?", "[email protected]").Joins("JOIN credit_cards ON credit_cards.user_id = users.id").Where("credit_cards.number = ?", "411111111111").Find(&user)
Pluck
Pluck，查询 model 中的一个列作为切片，如果想要查询多个列，应该使用Scan或者Find
var ages []int64
db.Find(&users).Pluck("age", &ages)
var names []string
db.Model(&User{
}).Pluck("name", &names)
db.Table("deleted_users").Pluck("name", &names)
// 想查询多个字段？ 这样做：
db.Select("name, age").Find(&users)
扫描
Scan，扫描结果至一个 struct，用法类似Find
type Result struct {
Name string
Age int
}
var result Result
db.Table("users").Select("name, age").Where("name = ?", "Antonio").Scan(&result)
var results []Result
db.Table("users").Select("name, age").Where("id > ?", 0).Scan(&results)
// 原生 SQL
db.Raw("SELECT name, age FROM users WHERE name = ?", "Antonio").Scan(&result)
Scopes
Scopes，Scope是建立在链式操作的基础之上的。
基于它，你可以抽取一些通用逻辑，写出更多可重用的函数库。
func AmountGreaterThan1000(db *gorm.DB) *gorm.DB {
return db.Where("amount > ?", 1000)
}
func PaidWithCreditCard(db *gorm.DB) *gorm.DB {
return db.Where("pay_mode_sign = ?", "C")
}
func PaidWithCod(db *gorm.DB) *gorm.DB {
return db.Where("pay_mode_sign = ?", "C")
}
func OrderStatus(status []string) func (db *gorm.DB) *gorm.DB {
return func (db *gorm.DB) *gorm.DB {
return db.Scopes(AmountGreaterThan1000).Where("status IN (?)", status)
}
}
db.Scopes(AmountGreaterThan1000, PaidWithCreditCard).Find(&orders)
// 查找所有金额大于 1000 的信用卡订单
db.Scopes(AmountGreaterThan1000, PaidWithCod).Find(&orders)
// 查找所有金额大于 1000 的 COD 订单
db.Scopes(AmountGreaterThan1000, OrderStatus([]string{
"paid", "shipped"})).Find(&orders)
// 查找所有金额大于 1000 且已付款或者已发货的订单
分页
func Paginate(r *http.Request) func(db *gorm.DB) *gorm.DB {
return func (db *gorm.DB) *gorm.DB {
page, _ := strconv.Atoi(r.Query("page"))
if page == 0 {
page = 1
}
pageSize, _ := strconv.Atoi(r.Query("page_size"))
switch {
case pageSize > 100:
pageSize = 100
case pageSize <= 0:
pageSize = 10
}
offset := (page - 1) * perPasge
return db.Offset(offset).Limit(pageSize)
}
}
db.Scopes(Paginate(r)).Find(&users)
db.Scopes(Paginate(r)).Find(&articles)
更新
更新所有字段
Save()默认会更新该对象的所有字段，即使你没有赋值。
db.First(&user)
user.Name = "七米"
user.Age = 99
db.Save(&user)
UPDATE `users` SET `created_at` = '2020-02-16 12:52:20', `updated_at` = '2020-02-16 12:54:55', `deleted_at` = NULL, `name` = '七米', `age` = 99, `active` = true WHERE `users`.`deleted_at` IS NULL AND `users`.`id` = 1
更新修改字段
如果你只希望更新指定字段，可以使用Update或者Updates
// 更新单个属性，如果它有变化
db.Model(&user).Update("name", "hello")
UPDATE users SET name='hello', updated_at='2013-11-17 21:34:10' WHERE id=111;
// 根据给定的条件更新单个属性
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;
// 使用 map 更新多个属性，只会更新其中有变化的属性
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;
// 使用 struct 更新多个属性，只会更新其中有变化且为非零值的字段
db.Model(&user).Updates(User{
Name: "hello", Age: 18})
UPDATE users SET name='hello', age=18, updated_at = '2013-11-17 21:34:10' WHERE id = 111;
// 警告：当使用 struct 更新时，GORM只会更新那些非零值的字段
// 对于下面的操作，不会发生任何更新，"", 0, false 都是其类型的零值
db.Model(&user).Updates(User{
Name: "", Age: 0, Active: false})
更新选定字段
如果你想更新或忽略某些字段，你可以使用 Select，Omit
db.Model(&user).Select("name").Updates(map[string]interface{
}{
"name": "hello", "age": 18, "active": false})
UPDATE users SET name='hello', updated_at='2013-11-17 21:34:10' 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;
无Hooks更新
上面的更新操作会自动运行 model 的 BeforeUpdate, AfterUpdate 方法，更新 UpdatedAt 时间戳, 在更新时保存其 Associations, 如果你不想调用这些方法，你可以使用 UpdateColumn， UpdateColumns
// 更新单个属性，类似于 `Update`
db.Model(&user).UpdateColumn("name", "hello")
UPDATE users SET name='hello' WHERE id = 111;
// 更新多个属性，类似于 `Updates`
db.Model(&user).UpdateColumns(User{
Name: "hello", Age: 18})
UPDATE users SET name='hello', age=18 WHERE id = 111;
批量更新
批量更新时Hooks（钩子函数）不会运行。
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);
// 使用 struct 更新时，只会更新非零值字段，若想更新所有字段，请使用map[string]interface{}
db.Model(User{
}).Updates(User{
Name: "hello", Age: 18})
UPDATE users SET name='hello', age=18;
// 使用 `RowsAffected` 获取更新记录总数
db.Model(User{
}).Updates(User{
Name: "hello", Age: 18}).RowsAffected
使用SQL表达式更新
先查询表中的第一条数据保存至user变量。
var user User
db.First(&user)
db.Model(&user).Update("age", gorm.Expr("age * ? + ?", 2, 100))
UPDATE `users` SET `age` = age * 2 + 100, `updated_at` = '2020-02-16 13:10:20' WHERE `users`.`id` = 1;
db.Model(&user).Updates(map[string]interface{
}{
"age": gorm.Expr("age * ? + ?", 2, 100)})
UPDATE "users" SET "age" = age * '2' + '100', "updated_at" = '2020-02-16 13:05:51' WHERE `users`.`id` = 1;
db.Model(&user).UpdateColumn("age", gorm.Expr("age - ?", 1))
UPDATE "users" SET "age" = age - 1 WHERE "id" = '1';
db.Model(&user).Where("age > 10").UpdateColumn("age", gorm.Expr("age - ?", 1))
UPDATE "users" SET "age" = age - 1 WHERE "id" = '1' AND quantity > 10;
修改Hooks中的值
如果你想修改 BeforeUpdate, BeforeSave 等 Hooks 中更新的值，你可以使用 scope.SetColumn, 例如：
func (user *User) BeforeSave(scope *gorm.Scope) (err error) {
if pw, err := bcrypt.GenerateFromPassword(user.Password, 0); err == nil {
scope.SetColumn("EncryptedPassword", pw)
}
}
其它更新选项
// 为 update SQL 添加其它的 SQL
db.Model(&user).Set("gorm:update_option", "OPTION (OPTIMIZE FOR UNKNOWN)").Update("name", "hello")
UPDATE users SET name='hello', updated_at = '2013-11-17 21:34:10' WHERE id=111 OPTION (OPTIMIZE FOR UNKNOWN);
删除
删除记录
警告 删除记录时，请确保主键字段有值，GORM 会通过主键去删除记录，如果主键为空，GORM 会删除该 model 的所有记录。
// 删除现有记录
db.Delete(&email)
DELETE from emails where id=10;
// 为删除 SQL 添加额外的 SQL 操作
db.Set("gorm:delete_option", "OPTION (OPTIMIZE FOR UNKNOWN)").Delete(&email)
DELETE from emails where id=10 OPTION (OPTIMIZE FOR UNKNOWN);
批量删除
删除全部匹配的记录
db.Where("email LIKE ?", "%lixiaoyao%").Delete(Email{
})
DELETE from emails where email LIKE "%lixiaoyao%";
db.Delete(Email{
}, "email LIKE ?", "%lixiaoyao%")
DELETE from emails where email LIKE "%lixiaoyao%";
阻止全局删除
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
可以使用添加条件、原生SQL、允许AllowGlobalUpdate等方式来操作
db.Delete(&User{
}).Error // gorm.ErrMissingWhereClause
db.Where("1 = 1").Delete(&User{
})
// DELETE `users` WHERE 1=1
db.Exec("DELETE FROM users")
// DELETE FROM users
db.Session(&gorm.Session{
AllowGlobalUpdate: true}).Delete(&User{
})
// DELETE FROM users
返回删除数据
该功能需要数据库支持
// 返回所有列
var users []User
DB.Clauses(clause.Returning{
}).Where("role = ?", "admin").Delete(&users)
// DELETE FROM `users` WHERE role = "admin" RETURNING *
// users => []User{
{ID: 1, Name: "jinzhu", Role: "admin", Salary: 100}, {ID: 2, Name: "jinzhu.2", Role: "admin", Salary: 1000}}
// 返回指定列
DB.Clauses(clause.Returning{
Columns: []clause.Column{
{
Name: "name"}, {
Name: "salary"}}}).Where("role = ?", "admin").Delete(&users)
// DELETE FROM `users` WHERE role = "admin" RETURNING `name`, `salary`
// users => []User{
{ID: 0, Name: "jinzhu", Role: "", Salary: 100}, {ID: 0, Name: "jinzhu.2", Role: "", Salary: 1000}}
软删除
如果一个 model 有 DeletedAt 字段，他将自动获得软删除的功能！ 当调用 Delete 方法时， 记录不会真正的从数据库中被删除， 只会将DeletedAt 字段的值会被设置为当前时间
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;
// 查询记录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;
// Unscoped 方法可以查询被软删除的记录
db.Unscoped().Where("age = 20").Find(&users)
SELECT * FROM users WHERE age = 20;
Soft Delete
import "gorm.io/plugin/soft_delete"
type User struct {
ID uint
Name string
DeletedAt soft_delete.DeletedAt
}
// Query
SELECT * FROM users WHERE deleted_at = 0;
// Delete
UPDATE users SET deleted_at = /* current unix second */ WHERE ID = 1;
指定时间精度
deleted_at字段支持毫秒、纳秒级的时间戳精度，通过设置标签：gorm:“softDelete:milli”、gorm:“softDelete:nano”
type User struct {
ID uint
Name string
DeletedAt soft_delete.DeletedAt `gorm:"softDelete:milli"`
// DeletedAt soft_delete.DeletedAt `gorm:"softDelete:nano"`
}
// Query
SELECT * FROM users WHERE deleted_at = 0;
// Delete
UPDATE users SET deleted_at = /* current unix milli second or nano second */ WHERE ID = 1;
Flag模式
flag模式将使用 0, 1 来标记数据是否为删除, 1 标识已删除
type User struct {
ID uint
Name string
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;
混合模式
混合模式使用 0, 1 来标记数据是否为删除, 1 标识已删除，并且存储删除时间
type User struct {
ID uint
Name string
DeletedAt uint
IsDel soft_delete.DeletedAt `gorm:"softDelete:flag,DeletedAtField:DeletedAt"`
}
// Query
SELECT * FROM users WHERE is_del = 0;
// Delete
UPDATE users SET is_del = 1, deleted_at = /* current unix second */ WHERE ID = 1;
物理删除
// Unscoped 方法可以物理删除记录
db.Unscoped().Delete(&order)
DELETE FROM orders WHERE id=10;
SQL构造器
原生SQL
原生SQL查询
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)
执行原生 SQL
db.Exec("DROP TABLE users")
db.Exec("UPDATE orders SET shipped_at=? WHERE id IN ?", time.Now(), []int64{
1,2,3})
// SQL 表达式
DB.Exec("update users set money=? where name = ?", gorm.Expr("money * ? + ?", 10000, 1), "jinzhu")
命名参数
GORM 支持 sql.NamedArg 或 map[string]interface{}{} 命名参数，例如：
DB.Where("name1 = @name OR name2 = @name", sql.Named("name", "jinzhu")).Find(&user)
// SELECT * FROM `users` WHERE name1 = "jinzhu" OR name2 = "jinzhu"
DB.Where("name1 = @name OR name2 = @name", map[string]interface{
}{
"name": "jinzhu2"}).First(&result3)
// SELECT * FROM `users` WHERE name1 = "jinzhu2" OR name2 = "jinzhu2" ORDER BY `users`.`id` LIMIT 1
DB.Raw("SELECT * FROM users WHERE name1 = @name OR name2 = @name2 OR name3 = @name", sql.Named("name", "jinzhu1"), sql.Named("name2", "jinzhu2")).Find(&user)
// SELECT * FROM users WHERE name1 = "jinzhu1" OR name2 = "jinzhu2" OR name3 = "jinzhu1"
DB.Exec("UPDATE users SET name1 = @name, name2 = @name2, name3 = @name", sql.Named("name", "jinzhunew"), sql.Named("name2", "jinzhunew2"))
// UPDATE users SET name1 = "jinzhunew", name2 = "jinzhunew2", name3 = "jinzhunew"
DB.Raw("SELECT * FROM users WHERE (name1 = @name AND name3 = @name) AND name2 = @name2", map[string]interface{
}{
"name": "jinzhu", "name2": "jinzhu2"}).Find(&user)
// SELECT * FROM users WHERE (name1 = "jinzhu" AND name3 = "jinzhu") AND name2 = "jinzhu2"
DryRun 模式
在不执行的情况下生成 SQL ，可以用于准备或测试生成的 SQL (需要开启支持)
stmt := DB.Session(&Session{
DryRun: true}).First(&user, 1).Statement
stmt.SQL.String() //=> SELECT * FROM `users` WHERE `id` = $1 ORDER BY `id`
stmt.Vars //=> []interface{}{1}
分句(Clauses)
GORM 内部使用 SQL builder 生成 SQL。对于每个操作，GORM 都会创建一个 *gorm.Statement 对象，所有的 GORM API 都是在为 statement 添加/修改 Clause，最后，GORM 会根据这些 Clause 生成 SQL
例如，当通过 First 进行查询时，它会在 Statement 中添加以下 Clause
clause.Select{
Columns: "*"}
clause.From{
Tables: clause.CurrentTable}
clause.Limit{
Limit: 1}
clause.OrderByColumn{
Column: clause.Column{
Table: clause.CurrentTable, Name: clause.PrimaryKey},
}
然后 GORM 在回调中构建最终的查询 SQL，像这样：
Statement.Build("SELECT", "FROM", "WHERE", "GROUP BY", "ORDER BY", "LIMIT", "FOR")
生成 SQL：
SELECT * FROM `users` ORDER BY `users`.`id` LIMIT 1
Clause 构建器
不同的数据库, Clause 可能会生成不同的 SQL，例如：
db.Offset(10).Limit(5).Find(&users)
// SQL Server 会生成
// SELECT * FROM "users" OFFSET 10 ROW FETCH NEXT 5 ROWS ONLY
// MySQL 会生成
// SELECT * FROM `users` LIMIT 5 OFFSET 10
之所以支持 Clause，是因为 GORM 允许数据库驱动程序通过注册 Clause Builder 来取代默认值，这儿有一个 Limit 的示例
参考：
https://gorm.io/docs/index.html
https://www.liwenzhou.com/posts/Go/gorm/