• GORM模型查询

    GORM模型查询

    model

    type CreditCard struct {
	gorm.Model
	Number string
	UserID uint
}
type CreateUsers struct {
	gorm.Model
	Name         string
	Email        *string
	Age          uint8
	Birthday     *time.Time
	MemberNumber sql.NullString
	ActivatedAt  sql.NullTime
	CreatedAt    time.Time
	UpdatedAt    time.Time
	CreditCard   CreditCard `gorm:"foreignKey:ID"`
}

    表数据：

    image-20211202082746321

    一、检索单个对象

    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

    1.1 First

    package main

import (
	"database/sql"
	"errors"
	"fmt"
	"gorm.io/driver/mysql"
	"gorm.io/gorm"
	"time"
)

type CreditCard struct {
	gorm.Model
	Number string
	UserID uint
}
type CreateUsers struct {
	gorm.Model
	Name         string
	Email        *string
	Age          uint8
	Birthday     *time.Time
	MemberNumber sql.NullString
	ActivatedAt  sql.NullTime
	CreatedAt    time.Time
	UpdatedAt    time.Time
	CreditCard   CreditCard `gorm:"foreignKey:ID"`
}

func (u *CreateUsers) BeforeCreate(tx *gorm.DB) (err error) {
	fmt.Println("创建之前触发钩子")
	if u.Name == "RandySun" {
		return errors.New("invalid role")
	}
	return
}
func main() {
	dsn := "root:@tcp(127.0.0.1:3306)/gorm?charset=utf8mb4&parseTime=True&loc=Local"
	db, err := gorm.Open(mysql.Open(dsn), &gorm.Config{})
	if err != nil {
		panic(err)
	}
	// 迁移表创建对应关系
	db.AutoMigrate(&CreateUsers{}, &CreditCard{})

	// 查询
	var user  CreateUsers
	// 获取第一条记录（主键升序）
    // SELECT * FROM `create_users` WHERE `create_users`.`deleted_at` IS NULL ORDER BY `create_users`.`id` LIMIT 1
	db.Debug().First(&user)
	fmt.Printf(user.Name)	
}

    image-20211202083012514

    1.2 Take

    package main

import (
	"database/sql"
	"errors"
	"fmt"
	"gorm.io/driver/mysql"
	"gorm.io/gorm"
	"time"
)

func main() {
	dsn := "root:@tcp(127.0.0.1:3306)/gorm?charset=utf8mb4&parseTime=True&loc=Local"
	db, err := gorm.Open(mysql.Open(dsn), &gorm.Config{})
	if err != nil {
		panic(err)
	}
	// 迁移表创建对应关系
	db.AutoMigrate(&CreateUsers{}, &CreditCard{})

	// 查询
	var user  CreateUsers
	// 获取一条记录，没有指定排序字段
    //  SELECT * FROM `create_users` WHERE `create_users`.`deleted_at` IS NULL LIMIT 1
	db.Debug().Take(&user)
	fmt.Printf(user.Name)	
}

    1.3 Last

    package main

import (
	"database/sql"
	"errors"
	"fmt"
	"gorm.io/driver/mysql"
	"gorm.io/gorm"
	"time"
)

func main() {
	dsn := "root:@tcp(127.0.0.1:3306)/gorm?charset=utf8mb4&parseTime=True&loc=Local"
	db, err := gorm.Open(mysql.Open(dsn), &gorm.Config{})
	if err != nil {
		panic(err)
	}
	// 迁移表创建对应关系
	db.AutoMigrate(&CreateUsers{}, &CreditCard{})

	// 查询
	var user  CreateUsers
	// 获取最后一条记录（主键降序）
    // SELECT * FROM `create_users` WHERE `create_users`.`deleted_at` IS NULL ORDER BY `create_users`.`id` DESC LIMIT 1
	db.Debug().Last(&user)
	fmt.Println(user.ID, user.Name)
}

    image-20211202083316521

    1.4 返回结果

    package main

import (
	"database/sql"
	"errors"
	"fmt"
	"gorm.io/driver/mysql"
	"gorm.io/gorm"
	"time"
)

func main() {
	dsn := "root:@tcp(127.0.0.1:3306)/gorm?charset=utf8mb4&parseTime=True&loc=Local"
	db, err := gorm.Open(mysql.Open(dsn), &gorm.Config{})
	if err != nil {
		panic(err)
	}
	// 迁移表创建对应关系
	db.AutoMigrate(&CreateUsers{}, &CreditCard{})

	// 查询
	var user  CreateUsers
	result := db.First(&user)
	// 返回找到的记录数
	fmt.Println(result.RowsAffected)
	fmt.Println(result.Error) // returns error or nil

	// 检查 ErrRecordNotFound 错误
	isErrors := errors.Is(result.Error, gorm.ErrRecordNotFound)
	fmt.Println(isErrors)
}

    image-20211202083823224

    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  

// 有效，因为目标 struct 是指针
db.First(&user)
// SELECT * FROM `users` ORDER BY `users`.`id` LIMIT 1

    
// 有效，因为通过 `db.Model()` 指定了 mod
result := map[string]interface{}{}
db.Debug().Model(&CreateUsers{}).First(&result)
fmt.Printf("%#v\n", result)
fmt.Printf("%#v\n", result["name"])

    image-20211202084902277

    // 无效
result := map[string]interface{}{}
db.Table("create_users").First(&result)
fmt.Printf("%#v\n", result)
fmt.Printf("%#v\n", result["name"])

    image-20211202090215626

    // 配合 Take 有效
result := map[string]interface{}{}
db.Table("create_users").Take(&result) // 表名
fmt.Printf("%#v\n", result)
fmt.Printf("%#v\n", result["name"])

    image-20211202090115482

    // 未指定主键，会根据第一个字段排序(即：`Code`)
type Language struct {
  Code string
  Name string
}
db.First(&Language{})
// SELECT * FROM `languages` ORDER BY `languages`.`code` LIMIT 1

    二、用主键检索

    2.1 First

    package main

import (
	"database/sql"
	"errors"
	"fmt"
	"gorm.io/driver/mysql"
	"gorm.io/gorm"
	"time"
)

func main() {
	dsn := "root:@tcp(127.0.0.1:3306)/gorm?charset=utf8mb4&parseTime=True&loc=Local"
	db, err := gorm.Open(mysql.Open(dsn), &gorm.Config{})
	if err != nil {
		panic(err)
	}
	// 迁移表创建对应关系
	db.AutoMigrate(&CreateUsers{}, &CreditCard{})

	// 根据主键查询第一条记录
	var user CreateUsers
	db.Debug().First(&user, 5)
	fmt.Println(user.ID)
}

    image-20211202090602443

    2.2 First 字符串

    package main

import (
	"database/sql"
	"errors"
	"fmt"
	"gorm.io/driver/mysql"
	"gorm.io/gorm"
	"time"
)

func main() {
	dsn := "root:@tcp(127.0.0.1:3306)/gorm?charset=utf8mb4&parseTime=True&loc=Local"
	db, err := gorm.Open(mysql.Open(dsn), &gorm.Config{})
	if err != nil {
		panic(err)
	}
	// 迁移表创建对应关系
	db.AutoMigrate(&CreateUsers{}, &CreditCard{})

		// 根据主键查询第一条记录
	var user CreateUsers
	db.Debug().First(&user, "10")
	fmt.Println(user.ID)
}

    image-20211202090937960

    2.3 Find

    package main

import (
	"database/sql"
	"errors"
	"fmt"
	"gorm.io/driver/mysql"
	"gorm.io/gorm"
	"time"
)

func main() {
	dsn := "root:@tcp(127.0.0.1:3306)/gorm?charset=utf8mb4&parseTime=True&loc=Local"
	db, err := gorm.Open(mysql.Open(dsn), &gorm.Config{})
	if err != nil {
		panic(err)
	}
	// 迁移表创建对应关系
	db.AutoMigrate(&CreateUsers{}, &CreditCard{})
// 根据主键查询第多条记录
	var users []CreateUsers
	db.Debug().Find(&users, []int{1,2,3})
	
	for _, u :=range users{
		fmt.Println(u.ID)
	}
}

    image-20211202091304509

    2.4 检索全部对象

    package main

import (
	"database/sql"
	"errors"
	"fmt"
	"gorm.io/driver/mysql"
	"gorm.io/gorm"
	"time"
)

func main() {
	dsn := "root:@tcp(127.0.0.1:3306)/gorm?charset=utf8mb4&parseTime=True&loc=Local"
	db, err := gorm.Open(mysql.Open(dsn), &gorm.Config{})
	if err != nil {
		panic(err)
	}
	// 迁移表创建对应关系
	db.AutoMigrate(&CreateUsers{}, &CreditCard{})
    
	// 获取全部记录
	var users []CreateUsers
	result := db.Debug().Find(&users)

	fmt.Println(result.RowsAffected) // 返回找到的记录数，相当于 `len(users)`
	fmt.Println(result.Error)        // returns error
}

    image-20211202220356558

    image-20211202220435027

    三、Where String 条件

    3.1 条件查询First

    package main

import (
	"database/sql"
	"errors"
	"fmt"
	"gorm.io/driver/mysql"
	"gorm.io/gorm"
	"time"
)

func main() {
	dsn := "root:@tcp(127.0.0.1:3306)/gorm?charset=utf8mb4&parseTime=True&loc=Local"
	db, err := gorm.Open(mysql.Open(dsn), &gorm.Config{})
	if err != nil {
		panic(err)
	}
	// 迁移表创建对应关系
	db.AutoMigrate(&CreateUsers{}, &CreditCard{})
    
	var user CreateUsers
	db.Debug().Where("name = ?", "RandySun").First(&user)
	fmt.Println(user.ID)
}

    image-20211202222307102

    image-20211202222447952

    3.2 条件查询First

    package main

import (
	"database/sql"
	"errors"
	"fmt"
	"gorm.io/driver/mysql"
	"gorm.io/gorm"
	"time"
)

func main() {
	dsn := "root:@tcp(127.0.0.1:3306)/gorm?charset=utf8mb4&parseTime=True&loc=Local"
	db, err := gorm.Open(mysql.Open(dsn), &gorm.Config{})
	if err != nil {
		panic(err)
	}
	// 迁移表创建对应关系
	db.AutoMigrate(&CreateUsers{}, &CreditCard{})
    
	var user CreateUsers
	db.Debug().Where("name = ?", "RandySun").First(&user)
	fmt.Println(user.ID)
}

    3.3 全部查询

    package main

import (
	"database/sql"
	"errors"
	"fmt"
	"gorm.io/driver/mysql"
	"gorm.io/gorm"
	"time"
)

func main() {
	dsn := "root:@tcp(127.0.0.1:3306)/gorm?charset=utf8mb4&parseTime=True&loc=Local"
	db, err := gorm.Open(mysql.Open(dsn), &gorm.Config{})
	if err != nil {
		panic(err)
	}
	// 迁移表创建对应关系
	db.AutoMigrate(&CreateUsers{}, &CreditCard{})
    
   // 获取全部匹配的记录
    // SELECT * FROM `create_users` WHERE name <> 'RandySun' AND `create_users`.`deleted_at` IS NULL

	var users []CreateUsers
	db.Debug().Where("name <> ?", "RandySun").Find(&users)
	for _, u := range users{
		fmt.Println(u.ID, u.Name)
	}
}

    image-20211203083054241

    3.4 IN查询

    package main

import (
	"database/sql"
	"errors"
	"fmt"
	"gorm.io/driver/mysql"
	"gorm.io/gorm"
	"time"
)

func main() {
	dsn := "root:@tcp(127.0.0.1:3306)/gorm?charset=utf8mb4&parseTime=True&loc=Local"
	db, err := gorm.Open(mysql.Open(dsn), &gorm.Config{})
	if err != nil {
		panic(err)
	}
	// 迁移表创建对应关系
	db.AutoMigrate(&CreateUsers{}, &CreditCard{})
    
   	// IN
	var users []CreateUsers
	// SELECT * FROM `create_users` WHERE name IN ('RandySun','RandySun03') AND `create_users`.`deleted_at` IS NULL
	db.Debug().Where("name IN ?", []string{"RandySun", "RandySun03"}).Find(&users)
	for _, u := range users{
		fmt.Println(u.ID, u.Name)
	}
}

    3.5 LIKE

    package main

import (
	"database/sql"
	"errors"
	"fmt"
	"gorm.io/driver/mysql"
	"gorm.io/gorm"
	"time"
)

func main() {
	dsn := "root:@tcp(127.0.0.1:3306)/gorm?charset=utf8mb4&parseTime=True&loc=Local"
	db, err := gorm.Open(mysql.Open(dsn), &gorm.Config{})
	if err != nil {
		panic(err)
	}
	// 迁移表创建对应关系
	db.AutoMigrate(&CreateUsers{}, &CreditCard{})
    
  // LIKE
	var users []CreateUsers
	//  SELECT * FROM `create_users` WHERE name LIKE '%sun%' AND `create_users`.`deleted_at` IS NULL
	db.Debug().Where("name LIKE ?", "%sun%").Find(&users)
	for _, u := range users{
		fmt.Println(u.ID, u.Name)
	}
}

    image-20211203083610326

    3.6 AND

    package main

import (
	"database/sql"
	"errors"
	"fmt"
	"gorm.io/driver/mysql"
	"gorm.io/gorm"
	"time"
)

func main() {
	dsn := "root:@tcp(127.0.0.1:3306)/gorm?charset=utf8mb4&parseTime=True&loc=Local"
	db, err := gorm.Open(mysql.Open(dsn), &gorm.Config{})
	if err != nil {
		panic(err)
	}
	// 迁移表创建对应关系
	db.AutoMigrate(&CreateUsers{}, &CreditCard{})
    
    // AND
	var users []CreateUsers
	
    //  SELECT * FROM `create_users` WHERE (name = 'RandySun' AND age >= '18') AND `create_users`.`deleted_at` IS NULL
	db.Debug().Where("name = ? AND age >= ?", "RandySun", "18").Find(&users)
	// SELECT * FROM users WHERE name = 'jinzhu' AND age >= 22;
	for _, u := range users{
		fmt.Println(u.ID, u.Name)
	}
}

    image-20211203084041160

    3.7 Time

    package main

import (
	"database/sql"
	"errors"
	"fmt"
	"gorm.io/driver/mysql"
	"gorm.io/gorm"
	"time"
)

func main() {
	dsn := "root:@tcp(127.0.0.1:3306)/gorm?charset=utf8mb4&parseTime=True&loc=Local"
	db, err := gorm.Open(mysql.Open(dsn), &gorm.Config{})
	if err != nil {
		panic(err)
	}
	// 迁移表创建对应关系
	db.AutoMigrate(&CreateUsers{}, &CreditCard{})
    
   // Time
	var users []CreateUsers
	lasterWeek := time.Now()
	// SELECT * FROM `create_users` WHERE updated_at < '2021-12-03 08:43:00.694' AND `create_users`.`deleted_at` IS NULL

	db.Debug().Where("updated_at < ?", lasterWeek).Find(&users)
	for _, u := range users{
		fmt.Println(u.ID, u.Name)
	}
}

    image-20211203084400595

    3.8 BETWEEN

    package main

import (
	"database/sql"
	"errors"
	"fmt"
	"gorm.io/driver/mysql"
	"gorm.io/gorm"
	"time"
)

func main() {
	dsn := "root:@tcp(127.0.0.1:3306)/gorm?charset=utf8mb4&parseTime=True&loc=Local"
	db, err := gorm.Open(mysql.Open(dsn), &gorm.Config{})
	if err != nil {
		panic(err)
	}
	// 迁移表创建对应关系
	db.AutoMigrate(&CreateUsers{}, &CreditCard{})
    
   	// BETWEEN
	var users []CreateUsers

	// SELECT * FROM `create_users` WHERE (age BETWEEN 1 AND 18) AND `create_users`.`deleted_at` IS NULL
	db.Debug().Where("age BETWEEN ? AND ?", 1, 18).Find(&users)
	for _, u := range users{
		fmt.Println(u.ID, u.Name)
	}

}

    image-20211203084914543

    四 、Struct & Map查询

    4.1 Struct 查询

    package main

import (
	"database/sql"
	"errors"
	"fmt"
	"gorm.io/driver/mysql"
	"gorm.io/gorm"
	"time"
)

func main() {
	dsn := "root:@tcp(127.0.0.1:3306)/gorm?charset=utf8mb4&parseTime=True&loc=Local"
	db, err := gorm.Open(mysql.Open(dsn), &gorm.Config{})
	if err != nil {
		panic(err)
	}
	// 迁移表创建对应关系
	db.AutoMigrate(&CreateUsers{}, &CreditCard{})
    
   	// Struct
	var user CreateUsers
    // SELECT * FROM `create_users` WHERE `create_users`.`name` = 'RandySun' AND `create_users`.`age` = 18 AND `create_users`.`deleted_at` IS NULL ORDER BY `create_users`.`id` LIMIT 1
	db.Debug().Where(&CreateUsers{Name: "RandySun", Age: 18}).First(&user)
	fmt.Println(user.ID, user.Name)

}

    image-20211203085313242

    4.2 Map 查询

    package main

import (
	"database/sql"
	"errors"
	"fmt"
	"gorm.io/driver/mysql"
	"gorm.io/gorm"
	"time"
)

func main() {
	dsn := "root:@tcp(127.0.0.1:3306)/gorm?charset=utf8mb4&parseTime=True&loc=Local"
	db, err := gorm.Open(mysql.Open(dsn), &gorm.Config{})
	if err != nil {
		panic(err)
	}
	// 迁移表创建对应关系
	db.AutoMigrate(&CreateUsers{}, &CreditCard{})
    
   //// Map
	var users []CreateUsers
    // SELECT * FROM `create_users` WHERE `age` = 18 AND `name` = 'RandySun' AND `create_users`.`deleted_at` IS NULL
	db.Debug().Where(map[string]interface{}{"name": "RandySun", "age": 18}).Find(&users)

	for _, u := range users{
		fmt.Println(u.ID, u.Name)
	}

}

    image-20211203085545241

    4.3 切片条件

    package main

import (
	"database/sql"
	"errors"
	"fmt"
	"gorm.io/driver/mysql"
	"gorm.io/gorm"
	"time"
)

func main() {
	dsn := "root:@tcp(127.0.0.1:3306)/gorm?charset=utf8mb4&parseTime=True&loc=Local"
	db, err := gorm.Open(mysql.Open(dsn), &gorm.Config{})
	if err != nil {
		panic(err)
	}
	// 迁移表创建对应关系
	db.AutoMigrate(&CreateUsers{}, &CreditCard{})
    
  	// 主键切片条件
	var users []CreateUsers
	// SELECT * FROM `create_users` WHERE `create_users`.`id` IN (18,8,1) AND `create_users`.`deleted_at` IS NULL
	db.Debug().Where([]int64{18, 8, 1}).Find(&users)
	for _, u := range users{
		fmt.Println(u.ID, u.Name)
	}


}

    image-20211203090111613

    注意 当使用结构作为条件查询时，GORM 只会查询非零值字段。这意味着如果您的字段值为 0、''、false 或其他 零值，该字段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
}

    如果想要包含零值查询条件，你可以使用 map，其会包含所有 key-value 的查询条件，例如：

    db.Where(map[string]interface{}{"Name": "jinzhu", "Age": 0}).Find(&users)
// SELECT * FROM users WHERE name = "jinzhu" AND age = 0;

    五、指定结构体查询字段

    当使用 struct 进行查询时，你可以通过向 Where() 传入 struct 来指定查询条件的字段、值、表名，例如：

    var users []CreateUsers
//  SELECT * FROM `create_users` WHERE `create_users`.`name` = 'RandySun' AND `create_users`.`age` = 0 AND `create_users`.`deleted_at` IS NULL
db.Debug().Where(&CreateUsers{Name: "RandySun"}, "name", "Age").Find(&users)
for _, u :=range users{
    fmt.Println(u.ID, u.Name)
}

    image-20211203213953587

    var users []CreateUsers
db.Debug().Where(&CreateUsers{Name: "RandySun"}, "Age").Find(&users)
for _, u :=range users{
    fmt.Println(u.ID, u.Name)
}

    image-20211203213927518

    六、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。

    var user CreateUsers
// 根据主键获取记录 (只适用于整形主键)
// SELECT * FROM `create_users` WHERE `create_users`.`id` = 18 AND `create_users`.`deleted_at` IS NULL ORDER BY `create_users`.`id` LIMIT 1
db.Debug().First(&user, 18)
fmt.Println(user.ID, user.Name)

    image-20211203214758233

    // 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")

var user CreateUsers
db.Debug().First(&user, "name = ?", "RandySun01")
fmt.Println(user.ID, user.Name)

var user1 CreateUsers
db.Debug().First(&user1, "id = ?", "2")
fmt.Println(user1.ID, user1.Name)

    image-20211203215928386

    // Plain SQL
var users []CreateUsers
// find可群查和单查
// SELECT * FROM `create_users` WHERE name = 'RandySun' AND `create_users`.`deleted_at` IS NULL

db.Debug().Find(&users, "name = ?", "RandySun")
for _, u :=range users{
    fmt.Println(u.ID, u.Name)
}

var user CreateUsers
// find单查
// SELECT * FROM `create_users` WHERE name = 'RandySun' AND `create_users`.`deleted_at` IS NULL
db.Debug().Find(&user, "name = ?", "RandySun")
fmt.Println(user.ID, user.Name)

    image-20211203221227001

    
// SELECT * FROM `create_users` WHERE (name <> 'RandySun' AND age >= 18) AND `create_users`.`deleted_at` IS NULL
db.Find(&users, "name <> ? AND age > ?", "jinzhu", 20)

    image-20211203221433555

    
// Struct
//  SELECT * FROM `create_users` WHERE `create_users`.`age` = 18 AND `create_users`.`deleted_at` IS NULL
db.Find(&users, User{Age: 20})

    image-20211203221629413

    // Map
var users []CreateUsers
// SELECT * FROM `create_users` WHERE `age` = 20 AND `create_users`.`deleted_at` IS NULL
db.Debug().Find(&users, map[string]interface{}{"age": 20})

for _, u :=range users{
    fmt.Println(u.ID, u.Name)
}

    image-20211203221816662

    七、Not 条件

    作用与 Where 类似的情形如下：

    // NOT
var user CreateUsers
//  SELECT * FROM `create_users` WHERE `name` <> 'RandySun' AND `create_users`.`deleted_at` IS NULL ORDER BY `create_users`.`id` LIMIT 1
db.Debug().Not("name", "RandySun").First(&user)
fmt.Println(user.ID, user.Name)

    image-20211203222145346

    // Not In
var users []CreateUsers
//  SELECT * FROM `create_users` WHERE `name` NOT IN ('RandySun','RandySun02') AND `create_users`.`deleted_at` IS NULL
db.Debug().Not("name", []string{"RandySun", "RandySun02"}).Find(&users)
for _, u :=range users{
    fmt.Println(u.ID, u.Name)
}

    image-20211207080240683

    // Not In slice of primary keys
// SELECT * FROM `create_users` WHERE `create_users`.`id` NOT IN (1,2,3) AND `create_users`.`deleted_at` IS NULL
var users []CreateUsers
db.Debug().Not([]int64{1,2,3}).Find(&users)
for _, u :=range users{
    fmt.Println(u.ID, u.Name)
}

    image-20211207080613164

    var users []CreateUsers
// SELECT * FROM `create_users` WHERE `create_users`.`deleted_at` IS NULL
db.Not([]int64{}).Find(&users)
for _, u :=range users{
    fmt.Println(u.ID, u.Name)
}
//// SELECT * FROM users;

    image-20211207082908264

    // Plain SQL
var users []CreateUsers
// SELECT * FROM `create_users` WHERE NOT name = 'RandySun' AND `create_users`.`deleted_at` IS NULL
db.Debug().Not("name = ?", "RandySun").Find(&users)

for _, u :=range users{
    fmt.Println(u.ID, u.Name)
}

    image-20211207083216053

    // Struct
var users []CreateUsers
// SELECT * FROM `create_users` WHERE `create_users`.`name` <> 'RandySun' AND `create_users`.`deleted_at` IS NULL
db.Debug().Not(CreateUsers{Name: "RandySun"}).Find(&users)
for _, u :=range users{
    fmt.Println(u.ID, u.Name)
}

    image-20211207083412855

    八、Or条件

    var users []CreateUsers

// SELECT * FROM `create_users` WHERE (name = 'RandySun' OR age = 20) AND `create_users`.`deleted_at` IS NULL
db.Debug().Where("name = ?", "RandySun").Or("age = ?", 20).Find(&users)

for _, u :=range users{
    fmt.Println(u.ID, u.Name)
}

    image-20211207083916734

    image-20211207083743914

    // Struct
var users []CreateUsers
// SELECT * FROM `create_users` WHERE ((name = 'RandySun') OR `create_users`.`name` = 'RandySun02') AND `create_users`.`deleted_at` IS NULL
db.Debug().Where("name = 'RandySun'").Or(CreateUsers{Name: "RandySun02"}).Find(&users)

for _, u :=range users{
    fmt.Println(u.ID, u.Name)
}

    image-20211207084224585

    // Map
var users []CreateUsers
// SELECT * FROM `create_users` WHERE ((name = 'RandySun') OR `name` = 'RandySun02') AND `create_users`.`deleted_at` IS NULL
db.Debug().Where("name = 'RandySun'").Or(map[string]interface{}{"name": "RandySun02"}).Find(&users)
for _, u :=range users{
    fmt.Println(u.ID, u.Name)
}

    image-20211207084429640

    九、Order

    指定从数据库检索记录时的排序方式

    // 多个 排序
var users []CreateUsers
// SELECT * FROM `create_users` WHERE `create_users`.`deleted_at` IS NULL ORDER BY age desc,name
db.Debug().Order("age desc").Order("name").Find(&users)

for _, u :=range users{
    fmt.Println(u.ID, u.Name)
}

    image-20211207085912823

    // 多个 order
var users []CreateUsers
// SELECT * FROM `create_users` WHERE `create_users`.`deleted_at` IS NULL ORDER BY age desc,name
db.Debug().Order("age desc").Order("name").Find(&users)
for _, u :=range users{
    fmt.Println(u.ID, u.Name)
}

    image-20211207090140915

    // 自定义排序ORDER BY FIELD()
var users []CreateUsers
db.Debug().Clauses(clause.OrderBy{
    Expression: clause.Expr{SQL: "FIELD(id,?)", Vars: []interface{}{[]int{1, 2, 3}}, WithoutParentheses: true},
}).Find(&users)

for _, u := range users {
    fmt.Println(u.ID, u.Name)
}

    image-20211207213617316

    十、Limit & Offset

    Limit 指定获取记录的最大数量 Offset 指定在开始返回记录之前要跳过的记录数量

    var users []CreateUsers
//  SELECT * FROM `create_users` WHERE `create_users`.`deleted_at` IS NULL LIMIT 3
db.Debug().Limit(3).Find(&users)

for _, u :=range users{
    fmt.Println(u.ID, u.Name)
}

    image-20211207213952899

    // 通过 -1 消除 Limit 条件
var users1 []CreateUsers
var users2 []CreateUsers

//  SELECT * FROM `create_users` WHERE `create_users`.`deleted_at` IS NULL LIMIT 10
//  SELECT * FROM `create_users` WHERE `create_users`.`deleted_at` IS NULL
db.Debug().Limit(10).Find(&users1).Limit(-1).Find(&users2)

//  SELECT * FROM `create_users` WHERE `create_users`.`deleted_at` IS NULL LIMIT 10
for _, u :=range users1{
    fmt.Println(u.ID, u.Name)
}
fmt.Println("*********************************************************")
//  SELECT * FROM `create_users` WHERE `create_users`.`deleted_at` IS NULL
for _, u :=range users2{
    fmt.Println(u.ID, u.Name)
}

    image-20211207214423502

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

    var users []CreateUsers
// SELECT * FROM `create_users` WHERE `create_users`.`deleted_at` IS NULL LIMIT 10 OFFSET 5
db.Debug().Limit(10).Offset(5).Find(&users)

for _, u :=range users{
    fmt.Println(u.ID, u.Name)
}

    image-20211207215438474

    // 通过 -1 消除 Offset 条件
db.Offset(10).Find(&users1).Offset(-1).Find(&users2)
// SELECT * FROM users OFFSET 10; (users1)
// SELECT * FROM users; (users2)

    查看 Pagination 学习如何写一个分页器

    十一、Group By & Having

    group by

    type Result struct {
    Date  time.Time
    Total int
    name string
}

var result Result
// SELECT name, sum(age) as total FROM `create_users` WHERE name LIKE 'Randy%' AND `create_users`.`deleted_at` IS NULL GROUP BY `name` ORDER BY `create_users`.`id` LIMIT 1
db.Debug().Model(&CreateUsers{}).Select("name, sum(age) as total").Where("name LIKE ?", "Randy%").Group("name").First(&result)

fmt.Println(result.Date, result.Total, result.name)

    image-20211207221005173

    image-20211207221029658

    Group By & Having

    
type Result struct {
    Date  time.Time
    Total int
    name string
}

var result []Result
//  SELECT name, sum(age) as total FROM `create_users` WHERE `create_users`.`deleted_at` IS NULL GROUP BY `name` HAVING name = 'RandySun'

db.Debug().Model(&CreateUsers{}).Select("name, sum(age) as total").Group("name").Having("name = ?", "RandySun").Find(&result)
for _, u :=range result{
    fmt.Println(u.name, u.Total, u.Date)
}

    image-20211207221605011

    image-20211207221624416

    type Result struct {
Date  *time.Time
Total int
name string
}

// SELECT name , sum(age) as total FROM `create_users` GROUP BY `name`
rows, err := db.Debug().Table("create_users").Select("name , sum(age) as total").Group("name").Rows()
for rows.Next() {
var r Result
err := rows.Scan(&r.name, &r.Total)
if err != nil {
fmt.Printf("scan failed, err:%v\n", err)
return
}
fmt.Printf("name: %s, Total: %d\n", r.name, r.Total)
}

    image-20211207223802832

    image-20211207223812994

    type Result struct {
    Date  *time.Time
    Total int
    name string
}
rows, err := db.Debug().Table("create_users").Select("name, sum(age) as total").Group("name").Having("sum(age) > ?", 10).Rows()

for rows.Next() {
    var r Result
    err := rows.Scan(&r.name, &r.Total)
    if err != nil {
        fmt.Printf("scan failed, err:%v\n", err)
        return
    }
    fmt.Printf("name: %s, Total: %d\n", r.name, r.Total)
}

    image-20211207224233341

    image-20211207224252920

    type Result struct {
    names string
    Total int
    Date  *time.Time
}
var r []Result

// SELECT name, sum(age) as total FROM `create_users` GROUP BY `name` HAVING sum(age) > 10
db.Debug().Table("create_users").Select("name, sum(age) as total").Group("name").Having("sum(age) > ?", 10).Scan(&r)
for _, r := range r{
    fmt.Println(r.names, r.Total)
}

    image-20211207225140648

    image-20211207225115151

    十二、Distinct

    从模型中选择不相同的值

    db.Distinct("name", "age").Order("name, age desc").Find(&results)

    Distinct 也可以配合 Pluck, Count 使用

    十三、Joins

    指定 Joins 条件

    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)

// 带参数的多表连接
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)

    十四、Joins 预加载

    您可以使用 Joins 实现单条 SQL 预加载关联记录，例如：

    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`;

    Join with conditions

    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;

    For more details, please refer to Preloading (Eager Loading).

    十五、Scan

    Scanning results into a struct works similarly to the way we use 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)

    十六、选择特定字段

    Select 允许您指定从数据库中检索哪些字段， 默认情况下，GORM 会检索所有字段。

    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;

    还可以看一看 智能选择字段

    十七、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;

    十八、FirstOrInitSelect

    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}

    十九、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}

    二十、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}

    二十一、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"}

    二十二、Attrs

    如果记录未找到，将使用参数创建 struct 和记录.

     // 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}

    二十三、Assign

    不管记录是否找到，都将参数赋值给 struct 并保存至数据库.

    // 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}

    高级查询

    子查询

    基于 *gorm.expr 的子查询

    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')));

    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。

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

// -1 取消 Offset 条件
db.Offset(10).Find(&users1).Offset(-1).Find(&users2)
//// SELECT * FROM users OFFSET 10; (users1)
//// SELECT * FROM users; (users2)

    总数

    Count，该 model 能获取的记录总数。

    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;

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

    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

    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)

    连接

    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 = ?", "jinzhu@example.org").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)

    扫描

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

    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：

    // 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)
}

    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。

    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;

    范围

    Scopes，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%'

    // 使用 Scanner/Valuer
type Users struct {
	gorm.Model
	//Name *string `gorm:"type:varchar(100);default:RandySun;comment:姓名"`
	Name sql.NullString `gorm:"type:varchar(100);default:RandySun;comment:姓名"`
	Age  int64
	// 设置默认值
}

db.Debug().Create(&Users{Name: sql.NullString{String: "", Valid: true}, Age: 19}) // 添加记录name默认为Null

    image-20211120220904299

    image-20211120220830798

    image-20211120220348541

    扩展创建选项

    例如PostgreSQL数据库中可以使用下面的方式实现合并插入, 有则更新, 无则插入。

    // 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;
    在当下的阶段，必将由程序员来主导，甚至比以往更甚。
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  • 原文地址：https://www.cnblogs.com/randysun/p/15626803.html
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