package main
import (
"gorm.io/driver/mysql"
"gorm.io/gorm"
"gorm.io/gorm/logger"
)
const MYSQL_ADDR="user:pass@tcp(127.0.0.1:3306)/dbname?charset=utf8mb4&parseTime=True&loc=Local"
var DB *gorm.DB
type User struct {
gorm.Model
Age int
Name string
}
func main() {
DB = openDB()
//创建表
DB.AutoMigrate(&User{})
//插入一条记录
DB.Create(&User{
Name: "dhy",
Age: 18,
})
}
func openDB() *gorm.DB {
//创建数据库连接
db, err := gorm.Open(mysql.Open(MYSQL_ADDR),
//开启info级别的日志输出
&gorm.Config{Logger: logger.Default.LogMode(logger.Info)})
if err != nil {
panic("failed to connect database")
}
return db
}
GORM 提供了 First
、Take
、Last
方法,以便从数据库中检索单个对象。当查询数据库时它添加了 LIMIT 1
条件,且没有找到记录时,它会返回 ErrRecordNotFound
错误
// 获取第一条记录(主键升序)
db.First(&user)
// SELECT * FROM users ORDER BY id LIMIT 1;
// 获取一条记录,没有指定排序字段
db.Take(&user)
// SELECT * FROM users LIMIT 1;
// 获取最后一条记录(主键降序)
db.Last(&user)
// SELECT * FROM users ORDER BY id DESC LIMIT 1;
result := db.First(&user)
result.RowsAffected // 返回找到的记录数
result.Error // returns error or nil
// 检查 ErrRecordNotFound 错误
errors.Is(result.Error, gorm.ErrRecordNotFound)
如果你想避免
ErrRecordNotFound
错误,你可以使用Find
,比如db.Limit(1).Find(&user)
,Find
方法可以接受struct和slice的数据。
First
和 Last
会根据主键排序,分别查询第一条和最后一条记录。 只有在目标 struct 是指针或者通过 db.Model()
指定 model 时,该方法才有效。 此外,如果相关 model 没有定义主键,那么将按 model 的第一个字段进行排序。 例如:
var user User
var users []User
// works because destination struct is passed in
db.First(&user)
// SELECT * FROM `users` ORDER BY `users`.`id` LIMIT 1
// works because model is specified using `db.Model()`
result := map[string]interface{}{}
db.Model(&User{}).First(&result)
// SELECT * FROM `users` ORDER BY `users`.`id` LIMIT 1
// doesn't work
result := map[string]interface{}{}
db.Table("users").First(&result)
// works with Take
result := map[string]interface{}{}
db.Table("users").Take(&result)
// no primary key defined, results will be ordered by first field (i.e., `Code`)
type Language struct {
Code string
Name string
}
db.First(&Language{})
// SELECT * FROM `languages` ORDER BY `languages`.`code` LIMIT 1
如果主键是数字类型,您可以使用 内联条件 来检索对象。 传入字符串参数时,需要特别注意 SQL 注入问题,查看 安全 获取详情.
db.First(&user, 10)
// SELECT * FROM users WHERE id = 10;
db.First(&user, "10")
// SELECT * FROM users WHERE id = 10;
db.Find(&users, []int{1,2,3})
// SELECT * FROM users WHERE id IN (1,2,3);
如果主键是字符串(例如像 uuid),查询将被写成这样:
db.First(&user, "id = ?", "1b74413f-f3b8-409f-ac47-e8c062e3472a")
// SELECT * FROM users WHERE id = "1b74413f-f3b8-409f-ac47-e8c062e3472a";
当目标结构体存在名为ID的属性时,会将该属性作为主键去构建查询条件,例如:
var user = User{ID: 10}
db.First(&user)
// SELECT * FROM users WHERE id = 10;
var result User
db.Model(User{ID: 10}).First(&result)
// SELECT * FROM users WHERE id = 10;
// Get all records
result := db.Find(&users)
// SELECT * FROM users;
result.RowsAffected // returns found records count, equals `len(users)`
result.Error // returns error
// Get first matched record
db.Where("name = ?", "jinzhu").First(&user)
// SELECT * FROM users WHERE name = 'jinzhu' ORDER BY id LIMIT 1;
// Get all matched records
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';
// Struct
db.Where(&User{Name: "jinzhu", Age: 20}).First(&user)
// SELECT * FROM users WHERE name = "jinzhu" AND age = 20 ORDER BY id LIMIT 1;
// Map
db.Where(map[string]interface{}{"name": "jinzhu", "age": 20}).Find(&users)
// SELECT * FROM users WHERE name = "jinzhu" AND age = 20;
// Slice of primary keys
db.Where([]int64{20, 21, 22}).Find(&users)
// SELECT * FROM users WHERE id IN (20, 21, 22);
注意: 使用 struct 查询时,GORM 只会查询非零字段,这意味着如果您的字段的值为 0、‘’、false 或其他零值,则不会用于构建查询条件,例如:
db.Where(&User{Name: "jinzhu", Age: 0}).Find(&users)
// SELECT * FROM users WHERE name = "jinzhu";
要在查询条件中包含零值,您可以使用map,它将包含所有键值作为查询条件,例如:
db.Where(map[string]interface{}{"Name": "jinzhu", "Age": 0}).Find(&users)
// SELECT * FROM users WHERE name = "jinzhu" AND age = 0;
上面是默认使用结构体全部字段进行查询,我们还可以指定结构体中某几个字段参与查询:
db.Where(&User{Name: "jinzhu"}, "name", "Age").Find(&users)
// SELECT * FROM users WHERE name = "jinzhu" AND age = 0;
db.Where(&User{Name: "jinzhu"}, "Age").Find(&users)
// SELECT * FROM users WHERE age = 0;
查询条件可以以与 Where 类似的方式内联到 First 和 Find 等方法中。
// Get by primary key if it were a non-integer type
db.First(&user, "id = ?", "string_primary_key")
// SELECT * FROM users WHERE id = 'string_primary_key';
// 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;
db.Not("name = ?", "jinzhu").First(&user)
// SELECT * FROM users WHERE NOT name = "jinzhu" ORDER BY id LIMIT 1;
// Not In
db.Not(map[string]interface{}{"name": []string{"jinzhu", "jinzhu 2"}}).Find(&users)
// SELECT * FROM users WHERE name NOT IN ("jinzhu", "jinzhu 2");
// Struct
db.Not(User{Name: "jinzhu", Age: 18}).First(&user)
// SELECT * FROM users WHERE name <> "jinzhu" AND age <> 18 ORDER BY id LIMIT 1;
// Not In slice of primary keys
db.Not([]int64{1,2,3}).First(&user)
// SELECT * FROM users WHERE id NOT IN (1,2,3) ORDER BY id LIMIT 1;
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", Age: 18}).Find(&users)
// SELECT * FROM users WHERE name = 'jinzhu' OR (name = 'jinzhu 2' AND age = 18);
// Map
db.Where("name = 'jinzhu'").Or(map[string]interface{}{"name": "jinzhu 2", "age": 18}).Find(&users)
// SELECT * FROM users WHERE name = 'jinzhu' OR (name = 'jinzhu 2' AND age = 18);
我们可以选择select某几个字段,从数据库返回,例如:
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;
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;
db.Clauses(clause.OrderBy{
Expression: clause.Expr{SQL: "FIELD(id,?)", Vars: []interface{}{[]int{1, 2, 3}}, WithoutParentheses: true},
}).Find(&User{})
// SELECT * FROM users ORDER BY FIELD(id,1,2,3)
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)
db.Offset(3).Find(&users)
// SELECT * FROM users OFFSET 3;
db.Limit(10).Offset(5).Find(&users)
// SELECT * FROM users OFFSET 5 LIMIT 10;
// Cancel offset condition with -1
db.Offset(10).Find(&users1).Offset(-1).Find(&users2)
// SELECT * FROM users OFFSET 10; (users1)
// SELECT * FROM users; (users2)
type result struct {
Date time.Time
Total int
}
db.Model(&User{}).Select("name, sum(age) as total").Where("name LIKE ?", "group%").Group("name").First(&result)
// SELECT name, sum(age) as total FROM `users` WHERE name LIKE "group%" GROUP BY `name` LIMIT 1
db.Model(&User{}).Select("name, sum(age) as total").Group("name").Having("name = ?", "group").Find(&result)
// SELECT name, sum(age) as total FROM `users` GROUP BY `name` HAVING name = "group"
rows, err := db.Table("orders").Select("date(created_at) as date, sum(amount) as total").Group("date(created_at)").Rows()
defer rows.Close()
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()
defer rows.Close()
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)
//Distinct函数等同于拼接: SELECT DISTINCT `name`,`age`
db.Distinct("name", "age").Order("name, age desc").Find(&results)
type result struct {
Name string
Email string
}
db.Model(&User{}).Select("users.name, emails.email").Joins("left join emails on emails.user_id = users.id").Scan(&result{})
// SELECT users.name, emails.email FROM `users` left join emails on emails.user_id = users.id
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)
// multiple joins with parameter
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)
db.Joins("Company").Find(&users)
// SELECT `users`.`id`,`users`.`name`,`users`.`age`,`Company`.`id` AS `Company__id`,`Company`.`name` AS `Company__name` FROM `users` LEFT JOIN `companies` AS `Company` ON `users`.`company_id` = `Company`.`id`;
db.Joins("Company", db.Where(&Company{Alive: true})).Find(&users)
// SELECT `users`.`id`,`users`.`name`,`users`.`age`,`Company`.`id` AS `Company__id`,`Company`.`name` AS `Company__name` FROM `users` LEFT JOIN `companies` AS `Company` ON `users`.`company_id` = `Company`.`id` AND `Company`.`alive` = true;
type User struct {
Id int
Age int
}
type Order struct {
UserId int
FinishedAt *time.Time
}
query := db.Table("order").Select("MAX(order.finished_at) as latest").Joins("left join user user on order.user_id = user.id").Where("user.age > ?", 18).Group("order.user_id")
db.Model(&Order{}).Joins("join (?) q on order.finished_at = q.latest", query).Scan(&results)
// SELECT `order`.`user_id`,`order`.`finished_at` FROM `order` join (SELECT MAX(order.finished_at) as latest FROM `order` left join user user on order.user_id = user.id WHERE user.age > 18 GROUP BY `order`.`user_id`) q on order.finished_at = q.latest
将结果输入进结构体数组中,作用类似find
type Result struct {
Name string
Age int
}
var result Result
db.Table("users").Select("name", "age").Where("name = ?", "Antonio").Scan(&result)
// Raw SQL
db.Raw("SELECT name, age FROM users WHERE name = ?", "Antonio").Scan(&result)
Gorm框架高级查询的使用,这里就不列举了,官方文档已经给出了详细的介绍: https://gorm.io/zh_CN/docs/advanced_query.html