gorm session用法

GORM查询操作

一.一般查询

//根据主键获取第一条记录
var user User 
db.Debug().First(&user) //根据主键(必须存在,并且为数字类型)排序查询第一条记录,并将数据封装到user之中
//SELECT * FROM `users`  WHERE `users`.`deleted_at` IS NULL ORDER BY `users`.`id` ASC LIMIT 1

//根据主键获取最后一条记录
var user User 
db.Debug().Last(&user)
//SELECT * FROM `users`  WHERE `users`.`deleted_at` IS NULL ORDER BY `users`.`id` DESC LIMIT 1

//随机获取一条记录
var user User 
db.Debug().Take(&user)
fmt.Printf("user:%#v\n", user)
//SELECT * FROM `users`  WHERE `users`.`deleted_at` IS NULL LIMIT 1

// 查询列表
var users []User
db.Debug().Find(&users)
fmt.Printf("user:%#v\n", users)
//SELECT * FROM `users`  WHERE `users`.`deleted_at` IS NULL

// 查询指定的某条记录(仅当主键为整型时可以用)
var user User
db.Debug().First(&user,2)
//SELECT * FROM `users`  WHERE `users`.`deleted_at` IS NULL AND ((`users`.`id` = 2)) ORDER BY `users`.`id` ASC LIMIT 1

二.Where条件查询

//获取符合条件的第一条件记录
var user User
db.Where("name = ?","皮浩").Debug().First(&user)
//SELECT * FROM `users`  WHERE `users`.`deleted_at` IS NULL AND ((name = '皮浩')) ORDER BY `users`.`id` ASC LIMIT 1

//获取符合条件的所有记录
var users []User
db.Where("name = ?","皮浩").Debug().Find(&users)
//SELECT * FROM `users`  WHERE `users`.`deleted_at` IS NULL AND ((name = '皮浩'))

// 不等于 <>
var users []User
db.Where("name <> ?","皮").Debug().Find(&users)
// SELECT * FROM `users`  WHERE `users`.`deleted_at` IS NULL AND ((name <> '皮'))

// in 
var users []User
db.Where("name not in (?)",[]string{"哈哈","呵呵"}).Debug().Find(&users)
//SELECT * FROM `users`  WHERE `users`.`deleted_at` IS NULL AND ((name not in ('哈哈','呵呵')))

// like
var users []User
db.Where("name like ?","%皮%").Debug().Find(&users)
//SELECT * FROM `users`  WHERE `users`.`deleted_at` IS NULL AND ((name like '%皮%'))

// and 多个条件
var users []User
db.Where("name = ? and age > ?","皮浩",10).Debug().Find(&users)
//SELECT * FROM `users`  WHERE `users`.`deleted_at` IS NULL AND ((name = '皮浩' and age > 10))

// Time
var users []User
db.Where("updated_at < ?",time.Now()).Debug().Find(&users)
SELECT * FROM `users`  WHERE `users`.`deleted_at` IS NULL AND ((updated_at < '2021-06-28 21:41:18'))

// between
var users []User	
db.Where("created_at between ? and ?",time.Now().AddDate(0,0,-1),time.Now()).Debug().Find(&users)
//SELECT * FROM `users`  WHERE `users`.`deleted_at` IS NULL AND ((created_at between '2021-06-27 21:44:39' and '2021-06-28 21:44:39'))

三.Struct&Map查询

//传入结构体
var users []User
db.Where(&User{Name: "皮浩",Age: 18}).Debug().Find(&users)
//SELECT * FROM `users`  WHERE `users`.`deleted_at` IS NULL AND ((`users`.`name` = '皮浩') AND (`users`.`age` = 18))

//传入map
var users []User
db.Where(map[string]interface{}{"name":"皮浩","age":18}).Debug().Find(&users)
//SELECT * FROM `users`  WHERE `users`.`deleted_at` IS NULL AND ((`users`.`name` = '皮浩') AND (`users`.`age` = 18))

//主键的切片
var users []User
db.Where([]int64{1,2}).Debug().Find(&users)
//SELECT * FROM `users`  WHERE `users`.`deleted_at` IS NULL AND ((`users`.`id` IN (1,2)))

特别注意:当通过结构体进行查询时,gorm将会只使用非零值字段作为条件查询,比如0,false,''或者其他零值,将不会作为条件

Not条件

作用与Where类型类似

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";

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';

内联条件

作用于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;

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)

var user User
db.Debug().FirstOrInit(&user,User{Name: "小白",Age: 22})
//SELECT * FROM `users`  WHERE `users`.`deleted_at` IS NULL AND ((`users`.`name` = '小白') AND (`users`.`age` = 22)) ORDER BY `users`.`id` ASC LIMIT 1

Attrs

如果上述条件没查询到,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}

Assign

与Attr区分开,不管有没有查询到记录,都将赋值给结构体

var user User
db.Debug().Assign(User{Age: 99}).FirstOrInit(&user,User{Name: "皮浩"})
fmt.Printf("user:%#v\n", user)
//SELECT * FROM `users`  WHERE `users`.`deleted_at` IS NULL AND ((`users`.`name` = '皮浩')) ORDER BY `users`.`id` ASC LIMIT 1  查到了值,但是age被赋值为了99

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"}

Attrs

如果记录未找到,将使用参数创建struct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: "jinzhu"}).Attrs(User{Age: 30}).FirstOrCreate(&user)
 SELECT * FROM users WHERE name = 'jinzhu';
 user -> User{Id: 111, Name: "jinzhu", Age: 20}

Assign

不管记录是否找到,都将参数赋值给struct并保存到数据库

// 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: "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}

四.高级查询

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

// offer配置limit使用,否则无效
var users []User
db.Offset(1).Limit(2).Debug().Find(&users)
//SELECT * FROM `users`  WHERE `users`.`deleted_at` IS NULL LIMIT 2 OFFSET 1

数量

Count，该 model 能获取的记录总数。

//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
var users []User
var count int
db.Where("name = ?", "小白").Or("name = ?", "皮").Find(&users).Debug().Count(&count)
//SELECT count(*) FROM `users`  WHERE `users`.`deleted_at` IS NULL AND ((name = '皮浩') OR (name = '皮'))  

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;

db.Table("deleted_users").Select("count(distinct(name))").Count(&count)
 SELECT count( distinct(name) ) FROM deleted_users; (count)

表关联

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 = ?", "[e-mail]").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，如果您想要查询多个列，您应该使用 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)

// 想查询多个字段？ 这样做：
db.Select("name, age").Find(&users)

Scan

扫描结果至一个struct

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

五.链式操作相关

链式操作

Method Chaining，Gorm 实现了链式操作接口，所以你可以把代码写成这样：

//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


// 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)
}

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)

生成的SQL语句如下：

SELECT * FROM users where name = 'jinzhu' AND age = 30 AND active = 1;

Scop

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

多个立即执行方法

Multiple Immediate Methods，在 GORM 中使用多个立即执行方法时，后一个立即执行方法会复用前一个立即执行方法的条件 (不包括内联条件) 。

db.Where("name LIKE ?", "jinzhu%").Find(&users, "id IN (?)", []int{1, 2, 3}).Count(&count)

//生成的sql:
//SELECT * FROM users WHERE name LIKE 'jinzhu%' AND id IN (1, 2, 3)
//SELECT count(*) FROM users WHERE name LIKE 'jinzhu%'