type User struct {
    gorm.Model
    Name     string
    Age      int
    Birthday time.Time
}

1 添加

(1) db.Create()

使用NewRecord()查询主键是否存在
主键为空使用Create()创建记录 ```go // 添加单个记录 user := User{Name: “Jinzhu”, Age: 18, Birthday: time.Now()} db.Create(&user)

// 添加多条记录 var users = []User{ {Name: “jinzhu1”, Birthday: time.Now()}, {Name: “jinzhu2”, Birthday: time.Now()}, {Name: “jinzhu3”, Birthday: time.Now()}, } db.Create(&users)

<a name="tmdmS"></a>
## (2) 根据Map创建
```go
db.Model(&User{}).Create(map[string]interface{}{
  "Name": "jinzhu", "Age": 18,
})
// batch insert from `[]map[string]interface{}{}`
db.Model(&User{}).Create([]map[string]interface{}{
  {"Name": "jinzhu_1", "Age": 18},
  {"Name": "jinzhu_2", "Age": 20},
})

(3) 默认值

您可以通过标签 default 为字段定义默认值，如：

type User struct {
  ID   int64
  Name string `gorm:"default:galeone"`
  Age  int64  `gorm:"default:18"`
}

插入记录到数据库时，默认值会被用于填充值为零值的字段

注意对于声明了默认值的字段，像 0、’’、false 等零值是不会保存到数据库。您需要使用指针类型或 Scanner/Valuer 来避免这个问题，例如：

type User struct {
  gorm.Model
  Name string
  Age  *int           `gorm:"default:18"`
  Active sql.NullBool `gorm:"default:true"`
}

user := User{Age: new(int), Age: 18))} 
db.Create(&user)

user := User{Active: sql.NullBool{"", true}, Age:18}
db.Create(&user)

2 查询

(1) 查询单个记录

// 根据主键查询第一条记录
db.First(&user)  // SELECT * FROM users ORDER BY id 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;
// Get first matched record
db.Where("name = ?", "jinzhu").First(&user)
// SELECT * FROM users WHERE name = 'jinzhu' limit 1;

(2) 检索多个记录

// 查询所有的记录
db.Find(&users)  // SELECT * FROM users;
// Get all matched records
db.Where("name = ?", "jinzhu").Find(&users)
// SELECT * FROM users WHERE name = 'jinzhu';
// <>
db.Where("name <> ?", "jinzhu").Find(&users)
// SELECT * FROM users WHERE name <> 'jinzhu';
// IN
db.Where("name IN (?)", []string{"jinzhu", "jinzhu 2"}).Find(&users)
// SELECT * FROM users WHERE name in ('jinzhu','jinzhu 2');
// LIKE
db.Where("name LIKE ?", "%jin%").Find(&users)
// SELECT * FROM users WHERE name LIKE '%jin%';
// AND
db.Where("name = ? AND age >= ?", "jinzhu", "22").Find(&users)
// SELECT * FROM users WHERE name = 'jinzhu' 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';

(3) Struct & Map查询

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

提示：当通过Struct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: "jinzhu", Age: 0}).Find(&users)
// SELECT * FROM users WHERE name = "jinzhu";

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
}

(4) Not条件

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";

(5) 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 = '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)
// SELECT * FROM users WHERE name = 'jinzhu' OR name = 'jinzhu 2';

(6) 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;
// Plain 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;

(7) 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;

(8) 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: "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}

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

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

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

(10) 高级查询

1) SubQuery

db.Where("amount > ?", db.Table("orders").Select("AVG(amount)").Where("state = ?", "paid").SubQuery()).Find(&orders)
// SELECT * FROM "orders"  WHERE "orders"."deleted_at" IS NULL AND (amount > (SELECT AVG(amount) FROM "orders"  WHERE (state = 'paid')));

2) select

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;

3) order

Order，指定从数据库中检索出记录的顺序。

// 多字段排序
db.Order("age desc, name").Find(&users)  // 法一
db.Order("age desc").Order("name").Find(&users)  // 法二
// SELECT * FROM users ORDER BY age desc, name;

4) limit

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;

5) offset

Offset，指定开始返回记录前要跳过的记录数。

db.Offset(3).Find(&users)

6) count

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

7) 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)

8) join

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 = ?", "jinzhu@example.org")
    .Joins("JOIN credit_cards ON credit_cards.user_id = users.id")
    .Where("credit_cards.number = ?", "411111111111").Find(&user)

9) Pluck

Pluck，查询 model 中的一个列作为切片

var ages []int64
db.Find(&users).Pluck("age", &ages)
var names []string
db.Model(&User).Pluck("name", &names)

10) Scan

Scan，查询 model 中的多个列作为切片

type Result struct {
  Name string
  Age  int
}
var result Result
db.Table("users").Select("name, age").Where("name = ?", "Antonio").Scan(&result)

(11) 链式操作

在调用立即执行方法前不会生成Query语句，借助这个特性你可以创建一个函数来处理一些通用逻辑。
Method Chaining，Gorm 实现了链式操作接口，所以你可以把代码写成这样：

// 创建一个查询
tx := db.Where("name = ?", "jinzhu")
// 添加更多条件
if someCondition {
    tx = tx.Where("age = ?", 20)
} else {
    tx = tx.Where("age = ?", 30)
}
if yetAnotherCondition {
    tx = tx.Where("active = ?", 1)
}

(12) 立即执行方法

Immediate methods ，立即执行方法是指那些会立即生成SQL语句并发送到数据库的方法, 他们一般是CRUD方法，比如：Create, First, Find, Take, Save, UpdateXXX, Delete, Scan, Row, Rows…
这有一个基于上面链式方法代码的立即执行方法的例子：

tx.Find(&user)  // SELECT * FROM users where name = 'jinzhu' AND age = 30 AND active = 1;

3 更新

// 法一
db.First(&user)
user.Name = "七米"
user.Age = 99
db.Save(&user)
// 法二
db.Model(&user).Update("name", "hello")
// 法三
db.Model(&user).Updates(map[string]interface{}{"name": "hello", "age": 18, "active": false})

4 删除

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。

// 删除一条现有记录
db.Delete(&email)
// 删除全部匹配的记录
db.Where("email LIKE ?", "%jinzhu%").Delete(Email{})
db.Delete(Email{}, "email LIKE ?", "%jinzhu%")
// 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， 只会将DeletedAt 字段的值会被设置为当前时间
// 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;
// 物理删除
db.Unscoped().Delete(&order)

5 原生SQL

db.Raw("SELECT name, age FROM users WHERE name = ?", "Antonio")

Golang

gorm增删改查