gorm CRUD:读写数据

• 操作的参数传入基本都是结构体的指针，同时完成CURD后，指针指向的结构体数据也将随着更新

1 创建 Create

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

var user= User{Age: 99, Name: ""}
db.Create(&user)

注意

• 通过tag,定义声明创建数据时，字段的默认值

2 查询

FindFirstLast

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

// 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;

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

2.1 Where

• where 条件的方式有以下两类

2.1.1 sql字符串拼接

// 获取第一个匹配记录
db.Where("name = ?", "jinzhu").First(&user)
//// SELECT * FROM users WHERE name = 'jinzhu' limit 1;

// 获取所有匹配记录
db.Where("name = ?", "jinzhu").Find(&users)
//// SELECT * FROM users WHERE name = 'jinzhu';

db.Where("name <> ?", "jinzhu").Find(&users)

// IN
db.Where("name in (?)", []string{"jinzhu", "jinzhu 2"}).Find(&users)

// LIKE
db.Where("name LIKE ?", "%jin%").Find(&users)

// AND
db.Where("name = ? AND age >= ?", "jinzhu", "22").Find(&users)

// Time
db.Where("updated_at > ?", lastWeek).Find(&users)

db.Where("created_at BETWEEN ? AND ?", lastWeek, today).Find(&users)

2.1.2 struct map slice

// Struct
db.Where(&User{Name: "jinzhu", Age: 20}).First(&user)
////注意：这两个user结构体是两个不同的对象
//// 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);

2.2 Not 与Where相似，取反

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";

2.3 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)

2.3 FirstOrCreate 获取数据，若无则创建

// 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"}

2.4 Select 获取只需要的字段，映射数据的结构体也只需配置这几个需要的字段

db.Select("name, age").Find(&users)
//// SELECT name, age FROM users;

2.5 Order 排序

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

2.6 Limit

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

2.7 Offset

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

2.8 Count

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)

2.9 Group & Having

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() {
    rows.Scan()
    ...
}

查询总结

• 支持链式操作
• 首先db.Where操作，最后通过Find、Last、First将数据映射到对象中。查询符合条件的数据有多条时，需要将数据映射到切片结构中，
  如上面实例 &users 实际是指 []*user

3.更新

3.1 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;

3.2 更新选择的字段

通过Model,确定具体的表

// 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;

4.删除

db.Where("email LIKE ?", "%jinzhu%").Delete(Email{})
//// 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