【寒江雪】Gorm文档

GORM 使用笔记

  数据库:MySQL

  编程语言:GO

数据库操作

连接

db,err :=gorm.Open("mysql","root:ms126127@(193.112.126.44:3306)/test?charset=utf8&parseTime=True")
    defer db.Close()

数据迁移

  自动迁移模式将保持更新到最新。

  警告：自动迁移仅仅会创建表，增加缺少的列和缺少的索引，并且不会改变现有列的类型或删除未使用的列以保护数据。(只增不减)

db.AutoMigrate(&User{})

db.AutoMigrate(&User{}, &Product{}, &Order{})

// 创建表时添加表后缀    我写了一个支持utf8编码的写法。
db.Set("gorm:table_options", "ENGINE=InnoDB  DEFAULT CHARSET=utf8 AUTO_INCREMENT=1;").AutoMigrate(&User{})

检查表是否存在

// 检查模型`User`表是否存在
db.HasTable(&User{})

// 检查表`users`是否存在
db.HasTable("users")

创建表

db.CreateTable(&MyTable{})

db.Set("gorm:table_options", "ENGINE=InnoDB  DEFAULT CHARSET=utf8 AUTO_INCREMENT=1;").CreateTable(&MyTable{})

删除表

// 删除模型`User`的表
db.DropTable(&User{})

// 删除表`users`
db.DropTable("users")

// 删除模型`User`的表和表`products`
db.DropTableIfExists(&User{}, "products")

//测试代码
    //db.CreateTable(&Table1{})         table1 被创建
    //db.CreateTable(&Table2{})         table2 被创建
    //db.CreateTable(&Table3{})         table3 被创建
    //db.DropTable(&MyTable{})          my_table 被删除
    //db.DropTableIfExists(&Table1{})   table1 被删除
    //db.DropTableIfExists(&Table2{},&Table4{}) table2 被删除
    //db.CreateTable(&Table4{})         table4 被创建
    //db.DropTableIfExists(&Table3{},&Table4{}) table3 和 table4 一起被删除

修改列

// 修改模型`User`的description列的数据类型为`text`
db.Model(&User{}).ModifyColumn("description", "text")

删除列

// 删除模型`User`的description列
db.Model(&User{}).DropColumn("description")

添加外键

// 添加外键
// 1st param : 外键字段
// 2nd param : 外键表(字段)
// 3rd param : ONDELETE
// 4th param : ONUPDATE
db.Model(&User{}).AddForeignKey("city_id", "cities(id)", "RESTRICT", "RESTRICT")

添加索引

// 为`name`列添加索引`idx_user_name`
db.Model(&User{}).AddIndex("idx_user_name", "name")

// 为`name`, `age`列添加索引`idx_user_name_age`
db.Model(&User{}).AddIndex("idx_user_name_age", "name", "age")

// 添加唯一索引
db.Model(&User{}).AddUniqueIndex("idx_user_name", "name")

// 为多列添加唯一索引
db.Model(&User{}).AddUniqueIndex("idx_user_name_age", "name", "age")

// 删除索引
db.Model(&User{}).RemoveIndex("idx_user_name")

模型定义

约定

gorm.Model结构体

// 基本模型的定义
type Model struct {
  ID        uint `gorm:"primary_key"`
  CreatedAt time.Time
  UpdatedAt time.Time
  DeletedAt *time.Time
}

// 添加字段 `ID`, `CreatedAt`, `UpdatedAt`, `DeletedAt`
type User struct {
  gorm.Model
  Name string
}

// 只需要字段 `ID`, `CreatedAt`
type User struct {
  ID        uint
  CreatedAt time.Time
  Name      string
}

表名是结构体名称的复数形式

type User struct {} // 默认表名是`users`

// 设置User的表名为`profiles`
func (User) TableName() string {
  return "profiles"
}

func (u User) TableName() string {
    if u.Role == "admin" {
        return "admin_users"
    } else {
        return "users"
    }
}

// 全局禁用表名复数
db.SingularTable(true) // 如果设置为true,`User`的默认表名为`user`,使用`TableName`设置的表名不受影响

更改默认表名

gorm.DefaultTableNameHandler = func (db *gorm.DB, defaultTableName string) string  {
    return "prefix_" + defaultTableName;
}

列名是字段名的蛇形小写

type User struct {
  ID uint             // 列名为 `id`
  Name string         // 列名为 `name`
  Birthday time.Time  // 列名为 `birthday`
  CreatedAt time.Time // 列名为 `created_at`
}

// 重设列名
type Animal struct {
    AnimalId    int64     `gorm:"column:beast_id"`         // 设置列名为`beast_id`
    Birthday    time.Time `gorm:"column:day_of_the_beast"` // 设置列名为`day_of_the_beast`
    Age         int64     `gorm:"column:age_of_the_beast"` // 设置列名为`age_of_the_beast`
}

字段ID为主键

type User struct {
  ID   uint  // 字段`ID`为默认主键
  Name string
}

// 使用tag`primary_key`用来设置主键
type Animal struct {
  AnimalId int64 `gorm:"primary_key"` // 设置AnimalId为主键
  Name     string
  Age      int64
}

字段CreatedAt用于存储记录的创建时间

db.Create(&user) // 将会设置`CreatedAt`为当前时间

// 要更改它的值, 你需要使用`Update`
db.Model(&user).Update("CreatedAt", time.Now())

字段UpdatedAt用于存储记录的修改时间

db.Save(&user) // 将会设置`UpdatedAt`为当前时间
db.Model(&user).Update("name", "jinzhu") // 将会设置`UpdatedAt`为当前时间

字段DeletedAt用于存储记录的删除时间，如果字段存在

  删除具有DeletedAt字段的记录，它不会冲数据库中删除，但只将字段DeletedAt设置为当前时间，并在查询时无法找到记录.

关联

属于

// `User`属于`Profile`, `ProfileID`为外键
type User struct {
  gorm.Model
  Profile   Profile
  ProfileID int
}

type Profile struct {
  gorm.Model
  Name string
}

db.Model(&user).Related(&profile)
//// SELECT * FROM profiles WHERE id = 111; // 111是user的外键ProfileID

指定外键

type Profile struct {
    gorm.Model
    Name string
}

type User struct {
    gorm.Model
    Profile      Profile `gorm:"ForeignKey:ProfileRefer"` // 使用ProfileRefer作为外键
    ProfileRefer int
}

指定外键和关联外键

type Profile struct {
    gorm.Model
    Refer string
    Name  string
}

type User struct {
    gorm.Model
    Profile   Profile `gorm:"ForeignKey:ProfileID;AssociationForeignKey:Refer"`
    ProfileID int
}

包含一个

// User 包含一个 CreditCard, UserID 为外键
type User struct {
    gorm.Model
    CreditCard   CreditCard
}

type CreditCard struct {
    gorm.Model
    UserID   uint
    Number   string
}

var card CreditCard
db.Model(&user).Related(&card, "CreditCard")
//// SELECT * FROM credit_cards WHERE user_id = 123; // 123 is user's primary key
// CreditCard是user的字段名称，这意味着获得user的CreditCard关系并将其填充到变量
// 如果字段名与变量的类型名相同，如上例所示，可以省略，如：
db.Model(&user).Related(&card)

包含多个

// User 包含多个 emails, UserID 为外键
type User struct {
    gorm.Model
    Emails   []Email
}

type Email struct {
    gorm.Model
    Email   string
    UserID  uint
}

db.Model(&user).Related(&emails)
//// SELECT * FROM emails WHERE user_id = 111; // 111 是 user 的主键

多对多

// User 包含并属于多个 languages, 使用 `user_languages` 表连接
type User struct {
    gorm.Model
    Languages         []Language `gorm:"many2many:user_languages;"`
}

type Language struct {
    gorm.Model
    Name string
}

db.Model(&user).Related(&languages, "Languages")
//// SELECT * FROM "languages" INNER JOIN "user_languages" ON "user_languages"."language_id" = "languages"."id" WHERE "user_languages"."user_id" = 111

多种包含

支持多种的包含一个和包含多个的关联

type Cat struct {
    Id    int
    Name  string
    Toy   Toy `gorm:"polymorphic:Owner;"`
}

type Dog struct {
    Id   int
    Name string
    Toy  Toy `gorm:"polymorphic:Owner;"`
}

type Toy struct {
    Id        int
    Name      string
    OwnerId   int
    OwnerType string
}

关联模式

// 开始关联模式
var user User
db.Model(&user).Association("Languages")
// `user`是源，它需要是一个有效的记录（包含主键）
// `Languages`是关系中源的字段名。
// 如果这些条件不匹配，将返回一个错误，检查它：
// db.Model(&user).Association("Languages").Error


// Query - 查找所有相关关联
db.Model(&user).Association("Languages").Find(&languages)


// Append - 添加新的many2many, has_many关联, 会替换掉当前 has_one, belongs_to关联
db.Model(&user).Association("Languages").Append([]Language{languageZH, languageEN})
db.Model(&user).Association("Languages").Append(Language{Name: "DE"})


// Delete - 删除源和传递的参数之间的关系，不会删除这些参数
db.Model(&user).Association("Languages").Delete([]Language{languageZH, languageEN})
db.Model(&user).Association("Languages").Delete(languageZH, languageEN)


// Replace - 使用新的关联替换当前关联
db.Model(&user).Association("Languages").Replace([]Language{languageZH, languageEN})
db.Model(&user).Association("Languages").Replace(Language{Name: "DE"}, languageEN)


// Count - 返回当前关联的计数
db.Model(&user).Association("Languages").Count()


// Clear - 删除源和当前关联之间的关系，不会删除这些关联
db.Model(&user).Association("Languages").Clear()

读写数据

创建

创建数据

user := User{Name: "Jinzhu", Age: 18, Birthday: time.Now()}

db.NewRecord(user) // => 主键为空返回`true`   

db.Create(&user)

db.NewRecord(user) // => 创建`user`后返回`false`

//  NewRecord只检查主键，不创建记录

默认值

type Animal struct {
    ID   int64
    Name string `gorm:"default:'galeone'"`
    Age  int64
}

var animal = Animal{Age: 99, Name: ""}
db.Create(&animal)
// INSERT INTO animals("age") values('99');
// SELECT name from animals WHERE ID=111; // 返回主键为 111
// animal.Name => 'galeone'

在Callbacks中设置主键

func (user *User) BeforeCreate(scope *gorm.Scope) error {
  scope.SetColumn("ID", uuid.New())
  return nil
}

扩展创建选项

// 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;

查询

// 获取第一条记录，按主键排序
db.First(&user)
//// SELECT * FROM users ORDER BY id LIMIT 1;

// 获取最后一条记录，按主键排序
db.Last(&user)
//// SELECT * FROM users ORDER BY id DESC LIMIT 1;

// 获取所有记录
db.Find(&users)
//// SELECT * FROM users;

// 使用主键获取记录
db.First(&user, 10)
//// SELECT * FROM users WHERE id = 10;

Where条件查询(简单SQL)

注意：当使用struct查询时，GORM将只查询那些具有值的字段

// Struct
db.Where(&User{Name: "jinzhu", Age: 20}).First(&user)
//// SELECT * FROM users WHERE name = "jinzhu" AND age = 20 LIMIT 1;

// Map
db.Where(map[string]interface{}{"name": "jinzhu", "age": 20}).Find(&users)
//// SELECT * FROM users WHERE name = "jinzhu" AND age = 20;

// 主键的Slice
db.Where([]int64{20, 21, 22}).Find(&users)
//// SELECT * FROM users WHERE id IN (20, 21, 22);

Not条件查询

db.Not("name", "jinzhu").First(&user)
//// SELECT * FROM users WHERE name <> "jinzhu" LIMIT 1;

// Not In
db.Not("name", []string{"jinzhu", "jinzhu 2"}).Find(&users)
//// SELECT * FROM users WHERE name NOT IN ("jinzhu", "jinzhu 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 = ?", "jinzhu").First(&user)
//// SELECT * FROM users WHERE NOT(name = "jinzhu");

// Struct
db.Not(User{Name: "jinzhu"}).First(&user)
//// SELECT * FROM users WHERE name <> "jinzhu";

带内联条件的查询

注意：使用主键查询时，应仔细检查所传递的值是否为有效主键，以避免SQL注入

// 按主键获取
db.First(&user, 23)
//// SELECT * FROM users WHERE id = 23 LIMIT 1;

// 简单SQL
db.Find(&user, "name = ?", "jinzhu")
//// SELECT * FROM users WHERE name = "jinzhu";

db.Find(&users, "name <> ? AND age > ?", "jinzhu", 20)
//// SELECT * FROM users WHERE name <> "jinzhu" 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;

Or条件查询

db.Where("role = ?", "admin").Or("role = ?", "super_admin").Find(&users)
//// SELECT * FROM users WHERE role = 'admin' OR role = 'super_admin';

// Struct
db.Where("name = 'jinzhu'").Or(User{Name: "jinzhu 2"}).Find(&users)
//// SELECT * FROM users WHERE name = 'jinzhu' OR name = 'jinzhu 2';

// Map
db.Where("name = 'jinzhu'").Or(map[string]interface{}{"name": "jinzhu 2"}).Find(&users)

查询链

Gorm有一个可链接的API，你可以这样使用它

db.Where("name <> ?","jinzhu").Where("age >= ? and role <> ?",20,"admin").Find(&users)
//// SELECT * FROM users WHERE name <> 'jinzhu' AND age >= 20 AND role <> 'admin';

db.Where("role = ?", "admin").Or("role = ?", "super_admin").Not("name = ?", "jinzhu").Find(&users)

扩展查询选项

// 为Select语句添加扩展SQL选项
db.Set("gorm:query_option", "FOR UPDATE").First(&user, 10)
//// SELECT * FROM users WHERE id = 10 FOR UPDATE;

FirstOrInit

获取第一个匹配的记录，或者使用给定的条件初始化一个新的记录（仅适用于struct，map条件）

// Unfound
db.FirstOrInit(&user, User{Name: "non_existing"})
//// user -> User{Name: "non_existing"}

// Found
db.Where(User{Name: "Jinzhu"}).FirstOrInit(&user)
//// user -> User{Id: 111, Name: "Jinzhu", Age: 20}
db.FirstOrInit(&user, map[string]interface{}{"name": "jinzhu"})
//// user -> User{Id: 111, Name: "Jinzhu", Age: 20}

Attrs

如果未找到记录，则使用参数初始化结构

// Unfound
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}

// Found
db.Where(User{Name: "Jinzhu"}).Attrs(User{Age: 30}).FirstOrInit(&user)
//// SELECT * FROM USERS WHERE name = jinzhu';
//// user -> User{Id: 111, Name: "Jinzhu", Age: 20}

Assign

将参数分配给结果，不管它是否被找到

// Unfound
db.Where(User{Name: "non_existing"}).Assign(User{Age: 20}).FirstOrInit(&user)
//// user -> User{Name: "non_existing", Age: 20}

// Found
db.Where(User{Name: "Jinzhu"}).Assign(User{Age: 30}).FirstOrInit(&user)
//// SELECT * FROM USERS WHERE name = jinzhu';
//// user -> User{Id: 111, Name: "Jinzhu", Age: 30}

FirstOrCreate

获取第一个匹配的记录，或创建一个具有给定条件的新记录（仅适用于struct, map条件）

// Unfound
db.FirstOrCreate(&user, User{Name: "non_existing"})
//// INSERT INTO "users" (name) VALUES ("non_existing");
//// user -> User{Id: 112, Name: "non_existing"}

// Found
db.Where(User{Name: "Jinzhu"}).FirstOrCreate(&user)
//// user -> User{Id: 111, Name: "Jinzhu"}

// 如果未找到记录，则为参数分配结构
// Unfound
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}

// Found
db.Where(User{Name: "jinzhu"}).Attrs(User{Age: 30}).FirstOrCreate(&user)
//// SELECT * FROM users WHERE name = 'jinzhu';
//// user -> User{Id: 111, Name: "jinzhu", Age: 20}

// 将其分配给记录，而不管它是否被找到，并保存回数据库。
// Unfound
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}

// Found
db.Where(User{Name: "jinzhu"}).Assign(User{Age: 30}).FirstOrCreate(&user)
//// SELECT * FROM users WHERE name = 'jinzhu';
//// UPDATE users SET age=30 WHERE id = 111;
//// user -> User{Id: 111, Name: "jinzhu", Age: 30}

Select

指定要从数据库检索的字段，默认情况下，将选择所有字段;

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;

Order

在从数据库检索记录时指定顺序，将重排序设置为true以覆盖定义的条件

db.Order("age desc, name").Find(&users)
//// SELECT * FROM users ORDER BY age desc, name;

// Multiple orders
db.Order("age desc").Order("name").Find(&users)
//// SELECT * FROM users ORDER BY age desc, name;

// ReOrder
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)

Limit

指定要检索的记录数

db.Limit(3).Find(&users)
//// SELECT * FROM users LIMIT 3;

// Cancel limit condition with -1
db.Limit(10).Find(&users1).Limit(-1).Find(&users2)
//// SELECT * FROM users LIMIT 10; (users1)
//// SELECT * FROM users; (users2)

Offset

指定在开始返回记录之前要跳过的记录数

db.Offset(3).Find(&users)
//// SELECT * FROM users OFFSET 3;

// Cancel offset condition with -1
db.Offset(10).Find(&users1).Offset(-1).Find(&users2)
//// SELECT * FROM users OFFSET 10; (users1)
//// SELECT * FROM users; (users2)

Count

获取模型的记录数

db.Where("name = ?", "jinzhu").Or("name = ?", "jinzhu 2").Find(&users).Count(&count)
//// SELECT * from USERS WHERE name = 'jinzhu' OR name = 'jinzhu 2'; (users)
//// SELECT count(*) FROM users WHERE name = 'jinzhu' OR name = 'jinzhu 2'; (count)

db.Model(&User{}).Where("name = ?", "jinzhu").Count(&count)
//// SELECT count(*) FROM users WHERE name = 'jinzhu'; (count)

db.Table("deleted_users").Count(&count)
//// SELECT count(*) FROM deleted_users;

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() {
    ...
}

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)

Join

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)

// 多个连接与参数
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

将模型中的单个列作为地图查询，如果要查询多个列，可以使用Scan

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)

// 要返回多个列，做这样：
db.Select("name, age").Find(&users)

Scan

将结果扫描到另一个结构中。

type Result struct {
    Name string
    Age  int
}

var result Result
db.Table("users").Select("name, age").Where("name = ?", 3).Scan(&result)

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

Scopes

将当前数据库连接传递到func(*DB) *DB，可以用于动态添加条件

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)
// 查找所有信用卡订单和金额大于1000

db.Scopes(AmountGreaterThan1000, PaidWithCod).Find(&orders)
// 查找所有COD订单和金额大于1000

db.Scopes(OrderStatus([]string{"paid", "shipped"})).Find(&orders)
// 查找所有付费，发货订单

指定表名

// 使用User结构定义创建`deleted_users`表
db.Table("deleted_users").CreateTable(&User{})

var deleted_users []User
db.Table("deleted_users").Find(&deleted_users)
//// SELECT * FROM deleted_users;

db.Table("deleted_users").Where("name = ?", "jinzhu").Delete()
//// DELETE FROM deleted_users WHERE name = 'jinzhu';

预加载

db.Preload("Orders").Find(&users)
//// SELECT * FROM users;
//// SELECT * FROM orders WHERE user_id IN (1,2,3,4);

db.Preload("Orders", "state NOT IN (?)", "cancelled").Find(&users)
//// SELECT * FROM users;
//// SELECT * FROM orders WHERE user_id IN (1,2,3,4) AND state NOT IN ('cancelled');

db.Where("state = ?", "active").Preload("Orders", "state NOT IN (?)", "cancelled").Find(&users)
//// SELECT * FROM users WHERE state = 'active';
//// SELECT * FROM orders WHERE user_id IN (1,2) AND state NOT IN ('cancelled');

db.Preload("Orders").Preload("Profile").Preload("Role").Find(&users)
//// SELECT * FROM users;
//// SELECT * FROM orders WHERE user_id IN (1,2,3,4); // has many
//// SELECT * FROM profiles WHERE user_id IN (1,2,3,4); // has one
//// SELECT * FROM roles WHERE id IN (4,5,6); // belongs to

自定义预加载SQL

您可以通过传递func(db *gorm.DB) *gorm.DB（与Scopes的使用方法相同）来自定义预加载SQL，例如：

db.Preload("Orders", func(db *gorm.DB) *gorm.DB {
    return db.Order("orders.amount DESC")
}).Find(&users)
//// SELECT * FROM users;
//// SELECT * FROM orders WHERE user_id IN (1,2,3,4) order by orders.amount DESC;

嵌套预加载

db.Preload("Orders.OrderItems").Find(&users)
db.Preload("Orders", "state = ?", "paid").Preload("Orders.OrderItems").Find(&users)

更新

更新全部字段

Save将包括执行更新SQL时的所有字段，即使它没有更改

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;

更新更改字段

如果只想更新更改的字段，可以使用Update, Updates

// 更新单个属性（如果更改）
db.Model(&user).Update("name", "hello")
//// UPDATE users SET name='hello', updated_at='2013-11-17 21:34:10' WHERE id=111;

// 使用组合条件更新单个属性
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，只会更新这些更改的字段
db.Model(&user).Updates(map[string]interface{}{"name": "hello", "age": 18, "actived": false})
//// UPDATE users SET name='hello', age=18, actived=false, updated_at='2013-11-17 21:34:10' WHERE id=111;

// 使用`struct`更新多个属性，只会更新这些更改的和非空白字段
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，FORM将仅更新具有非空值的字段
// 对于下面的更新，什么都不会更新因为""，0，false是其类型的空白值
db.Model(&user).Updates(User{Name: "", Age: 0, Actived: false})

更新选择的字段

如果您只想在更新时更新或忽略某些字段，可以使用Select, Omit

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

更新更改字段但不进行Callbacks

以上更新操作将执行模型的BeforeUpdate, AfterUpdate方法，更新其UpdatedAt时间戳，在更新时保存它的Associations，如果不想调用它们，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，与“更新”类似
db.Model(&user).UpdateColumns(User{Name: "hello", Age: 18})
//// UPDATE users SET name='hello', age=18 WHERE id = 111;

Batch Updates 批量更新

Callbacks在批量更新时不会运行

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更新仅适用于非零值，或使用map[string]interface{}
db.Model(User{}).Updates(User{Name: "hello", Age: 18})
//// UPDATE users SET name='hello', age=18;

// 使用`RowsAffected`获取更新记录计数
db.Model(User{}).Updates(User{Name: "hello", Age: 18}).RowsAffected

使用SQL表达式更新

DB.Model(&product).Update("price", gorm.Expr("price * ? + ?", 2, 100))
//// UPDATE "products" SET "price" = price * '2' + '100', "updated_at" = '2013-11-17 21:34:10' WHERE "id" = '2';

DB.Model(&product).Updates(map[string]interface{}{"price": gorm.Expr("price * ? + ?", 2, 100)})
//// UPDATE "products" SET "price" = price * '2' + '100', "updated_at" = '2013-11-17 21:34:10' WHERE "id" = '2';

DB.Model(&product).UpdateColumn("quantity", gorm.Expr("quantity - ?", 1))
//// UPDATE "products" SET "quantity" = quantity - 1 WHERE "id" = '2';

DB.Model(&product).Where("quantity > 1").UpdateColumn("quantity", gorm.Expr("quantity - ?", 1))
//// UPDATE "products" SET "quantity" = quantity - 1 WHERE "id" = '2' AND quantity > 1;

在Callbacks中更改更新值

如果要使用BeforeUpdate, BeforeSave更改回调中的更新值，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)
  }
}

额外更新选项

// 为Update语句添加额外的SQL选项
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/软删除

警告 删除记录时，需要确保其主要字段具有值，GORM将使用主键删除记录，如果主要字段为空，GORM将删除模型的所有记录

// 删除存在的记录
db.Delete(&email)
//// DELETE from emails where id=10;

// 为Delete语句添加额外的SQL选项
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

删除所有匹配记录

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

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

软删除

如果模型有DeletedAt字段，它将自动获得软删除功能！ 那么在调用Delete时不会从数据库中永久删除，而是只将字段DeletedAt的值设置为当前时间。

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;

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

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

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

关联

默认情况下，当创建/更新记录时，GORM将保存其关联，如果关联具有主键，GORM将调用Update来保存它，否则将被创建。

type Email struct {
    gorm.Model
    Email   string
    UserID  uint
}

type Language struct {
    gorm.Model
    Name string
}

type Address struct {
    ID       int            `gorm:"primary_key;identity;"`
    Address1 string         `gorm:"not null;unique"` // 设置字段为非空并唯一
    //Address2 string         `gorm:"type:varchar(100);unique"`
    UserID   int
}

type User2 struct{
    gorm.Model
    Name string
    BillingAddress Address  `gorm:"ForeignKey:UserID;AssociationForeignKey:ID"`
    ShippingAddress Address `gorm:"ForeignKey:UserID;AssociationForeignKey:ID"`
    Emails []Email
    Languages []Language
}

user := User2{
        Name:            "jinzhu",
        BillingAddress:  Address{Address1: "Billing Address - Address 2"},
        ShippingAddress: Address{Address1: "Shipping Address - Address 2"},
        Emails:          []Email{
            {Email: "[email protected]"},
            {Email: "jinzhu-2@[email protected]"},
        },
        Languages:       []Language{
            {Name: "ZH"},
            {Name: "EN"},
        },
    }

    db.Create(&user)
    //// BEGIN TRANSACTION;
    //// INSERT INTO "addresses" (address1) VALUES ("Billing Address - Address 1");
    //// INSERT INTO "addresses" (address1) VALUES ("Shipping Address - Address 1");
    //// INSERT INTO "users" (name,billing_address_id,shipping_address_id) VALUES ("jinzhu", 1, 2);
    //// INSERT INTO "emails" (user_id,email) VALUES (111, "[email protected]");
    //// INSERT INTO "emails" (user_id,email) VALUES (111, "[email protected]");
    //// INSERT INTO "languages" ("name") VALUES ('ZH');
    //// INSERT INTO user_languages ("user_id","language_id") VALUES (111, 1);
    //// INSERT INTO "languages" ("name") VALUES ('EN');
    //// INSERT INTO user_languages ("user_id","language_id") VALUES (111, 2);
    //// COMMIT;

创建/更新时跳过保存关联

默认情况下保存记录时，GORM也会保存它的关联，你可以通过设置gorm:save_associations为false跳过它。

db.Set("gorm:save_associations", false).Create(&user)

db.Set("gorm:save_associations", false).Save(&user)

tag设置跳过保存关联

您可以使用tag来配置您的struct，以便在创建/更新时不会保存关联

type User struct {
  gorm.Model
  Name      string
  CompanyID uint
  Company   Company `gorm:"save_associations:false"`
}

type Company struct {
  gorm.Model
  Name string
}