Go语言之GORM框架(三)——Hook(钩子)与Gorm的高级查询

Hook(钩子)

和我们在gin框架中讲解的Hook函数一样，我们也可以在定义Hook结构体，完成一些操作，相关接口声明如下：

type CreateUser interface {    //创建对象时使用的HookBeforeCreate() errorBeforeSave() errorAfterCreate() errorAfterSave() error
}type UpdateUser interface {BeforeUpdate() errorBeforeSave() errorAfterUpdate() errorAfterSave() error
}type DeleteUser interface {BeforeDelete() errorAfterDelete() error
}type FindUser interface {AfterFind() error
}

我们可以根据自己的需求来订制我们所需要的Hook函数，示例：

func (u *User) BeforeCreate(tx *gorm.DB) (err error) {u.UUID = uuid.New()if !u.IsValid() {err = errors.New("can't save invalid data")}return
}func (u *User) AfterCreate(tx *gorm.DB) (err error) {if u.ID == 1 {tx.Model(u).Update("role", "admin")}return
}

注意：

Hook函数在执行过程的执行时间有规定的时间，以创建对象的Hook为例：

// 开始事务
BeforeSave
BeforeCreate
// 关联前的 save
// 插入记录至 db
// 关联后的 save
AfterCreate
AfterSave
// 提交或回滚事务

具体可以参考官方文档：
Hook

在 GORM 中保存、删除操作会默认运行在事务上，因此在事务完成之前该事务中所作的更改是不可见的，如果Hook返回了任何错误，则修改将被回滚。

高级查询

初始化相关表

package mainimport ("fmt""gorm.io/driver/mysql""gorm.io/gorm""gorm.io/gorm/logger""log""os""time"
)type Employee struct {ID    uint    `gorm:"size:3"`Name  string  `gorm:"size:8"`Age   int     `gorm:"size:3"`Sex   bool    `gorm:"size:3"`Email *string `gorm:"size:32"`
}var myDB *gorm.DBfunc init() {//连接数据库user := "root"password := "ba161754"dbname := "gorm"ip := "127.0.0.1"port := "3306"dsn := fmt.Sprintf("%s:%s@tcp(%s:%s)/%s?charset=utf8mb4&parseTime=True&loc=Local", user, password, ip, port, dbname)db, err := gorm.Open(mysql.Open(dsn), &gorm.Config{})if err != nil {fmt.Println("数据库连接失败,err:", err)return}fmt.Println("数据库连接成功")myDB = db//初始化日志var mysqlLogger logger.InterfacemysqlLogger = logger.Default.LogMode(logger.Info) //设置日志打印级别mysqlLogger = logger.New(log.New(os.Stdout, "\r\n", log.LstdFlags), // （日志输出的目标，前缀和日志包含的内容）logger.Config{SlowThreshold:             time.Second, // 慢 SQL 阈值LogLevel:                  logger.Info, // 日志级别IgnoreRecordNotFoundError: true,        // 忽略ErrRecordNotFound（记录未找到）错误Colorful:                  true,        // 使用彩色打印},)myDB.Logger = mysqlLogger//创建所要使用的单表err = myDB.AutoMigrate(&Employee{})if err != nil {fmt.Println("创建表失败,err:", err)return}//插入测试数据employeeList := []Employee{{ID: 1, Name: "李元芳", Age: 32, Email: PtrString("lyf@yf.com"), Sex: true},{ID: 2, Name: "张武", Age: 18, Email: PtrString("zhangwu@lly.cn"), Sex: true},{ID: 3, Name: "枫枫", Age: 23, Email: PtrString("ff@yahoo.com"), Sex: true},{ID: 4, Name: "刘大", Age: 54, Email: PtrString("liuda@qq.com"), Sex: true},{ID: 5, Name: "李武", Age: 23, Email: PtrString("liwu@lly.cn"), Sex: true},{ID: 6, Name: "李琦", Age: 14, Email: PtrString("liqi@lly.cn"), Sex: false},{ID: 7, Name: "晓梅", Age: 25, Email: PtrString("xiaomeo@sl.com"), Sex: false},{ID: 8, Name: "如燕", Age: 26, Email: PtrString("ruyan@yf.com"), Sex: false},{ID: 9, Name: "魔灵", Age: 21, Email: PtrString("moling@sl.com"), Sex: true},}myDB.Create(&employeeList)
}func PtrString(email string) *string {return &email
}func main() {}

Where查询

简单示例：

	var employee Employee//WheremyDB.Where("name like ?", "李%").Find(&employee) //查询姓李的fmt.Println(employee)

Not条件

	myDB.Not("name like ?", "李%").Find(&employee) //查询第一条不是姓李的fmt.Println(employee)

Or条件

	var employeeList []EmployeemyDB.Not("name like ?", "李%").Or("age>20").Find(&employeeList)  //用Where表示andfor _, value := range employeeList {data, _ := json.Marshal(value)fmt.Println(string(data))}

And条件

	employeeList=[]Employee{}myDB.Not("name like ?", "李%").Where("age>20").Find(&employeeList)  //用Where表示andfor _, value := range employeeList {data, _ := json.Marshal(value)fmt.Println(string(data))}

select选择字段

简单示例

	employeeList := []Employee{}myDB.Select("name", "age").Find(&employeeList)for _, value := range employeeList {data, _ := json.Marshal(value)fmt.Println(string(data))}

Scan函数
我们可以用Scan函数将搜索结果导入带新的结构体中

type Employee1 struct {Name stringAge  int
}//selectemployeeList := []Employee{}employeeList1 := []Employee1{}myDB.Select("name", "age").Find(&employeeList).Scan(&employeeList1)for _, value := range employeeList1 {data, _ := json.Marshal(value)fmt.Println(string(data))}

输出为：
在这里插入图片描述

排序

	//排序employeeList := []Employee{}myDB.Order("age desc").Find(&employeeList)for _, value := range employeeList {data, _ := json.Marshal(value)fmt.Println(string(data))}

分页查询

	//分页employeeList := []Employee{}myDB.Limit(4).Offset(0).Order("age desc").Find(&employeeList) //Limit:每页限定记录数，offset:偏移量for _, value := range employeeList {data, _ := json.Marshal(value)fmt.Println(string(data))}

去重

	//去重var agelist []intmyDB.Table("employees").Select("distinct age").Find(&agelist)for _, value := range agelist {fmt.Println(value)}

分组查询

	//分组查询var ageList []int// 查询男生的个数和女生的个数myDB.Table("employees").Select("count(id)").Group("Sex").Scan(&ageList)fmt.Println(ageList)

执行原生sql

	//执行原生sqltype SexGroup struct {Count int `gorm:"column:count(id)"`Sex   boolName  string `gorm:"column:group_concat(name)"`}var sexlist []SexGroupmyDB.Raw("select count(id) ,sex,group_concat(name) from employees group by sex").Scan(&sexlist)for _, value := range sexlist {data, _ := json.Marshal(value)fmt.Println(string(data))}
}

子查询

	//子查询//select * from students where age > (select avg(age) from students); 原生sqlmyDB.Where("age > (?)", myDB.Model(&Employee{}).Select("avg(age)")).Find(&employee)fmt.Println(employee)

查询调用

我们可以在model层写一些通用的查询方法，让外界直接来调用：

func Age23(db *gorm.DB) *gorm.DB {return db.Where("age>?", 23)
}myDB.Scopes(Age23).Find(&employee)fmt.Println(employee)

完整代码

package mainimport ("encoding/json""fmt""gorm.io/driver/mysql""gorm.io/gorm""gorm.io/gorm/logger""log""os""time"
)type Employee struct {ID    uint    `gorm:"size:3"`Name  string  `gorm:"size:8"`Age   int     `gorm:"size:3"`Sex   bool    `gorm:"size:3"`Email *string `gorm:"size:32"`
}type Employee1 struct {Name stringAge  int
}var myDB *gorm.DBfunc init() {//连接数据库user := "root"password := "ba161754"dbname := "gorm"ip := "127.0.0.1"port := "3306"dsn := fmt.Sprintf("%s:%s@tcp(%s:%s)/%s?charset=utf8mb4&parseTime=True&loc=Local", user, password, ip, port, dbname)db, err := gorm.Open(mysql.Open(dsn), &gorm.Config{})if err != nil {fmt.Println("数据库连接失败,err:", err)return}fmt.Println("数据库连接成功")myDB = db//初始化日志var mysqlLogger logger.InterfacemysqlLogger = logger.Default.LogMode(logger.Info) //设置日志打印级别mysqlLogger = logger.New(log.New(os.Stdout, "\r\n", log.LstdFlags), // （日志输出的目标，前缀和日志包含的内容）logger.Config{SlowThreshold:             time.Second, // 慢 SQL 阈值LogLevel:                  logger.Info, // 日志级别IgnoreRecordNotFoundError: true,        // 忽略ErrRecordNotFound（记录未找到）错误Colorful:                  true,        // 使用彩色打印},)myDB.Logger = mysqlLogger//创建所要使用的单表err = myDB.AutoMigrate(&Employee{})if err != nil {fmt.Println("创建表失败,err:", err)return}//插入测试数据employeeList := []Employee{{ID: 1, Name: "李元芳", Age: 32, Email: PtrString("lyf@yf.com"), Sex: true},{ID: 2, Name: "张武", Age: 18, Email: PtrString("zhangwu@lly.cn"), Sex: true},{ID: 3, Name: "枫枫", Age: 23, Email: PtrString("ff@yahoo.com"), Sex: true},{ID: 4, Name: "刘大", Age: 54, Email: PtrString("liuda@qq.com"), Sex: true},{ID: 5, Name: "李武", Age: 23, Email: PtrString("liwu@lly.cn"), Sex: true},{ID: 6, Name: "李琦", Age: 14, Email: PtrString("liqi@lly.cn"), Sex: false},{ID: 7, Name: "晓梅", Age: 25, Email: PtrString("xiaomeo@sl.com"), Sex: false},{ID: 8, Name: "如燕", Age: 26, Email: PtrString("ruyan@yf.com"), Sex: false},{ID: 9, Name: "魔灵", Age: 21, Email: PtrString("moling@sl.com"), Sex: true},}myDB.Create(&employeeList)
}func PtrString(email string) *string {return &email
}func Age23(db *gorm.DB) *gorm.DB {return db.Where("age>?", 23)
}func main() {employee := Employee{}employeeList:=[]Employee{}//WheremyDB.Where("name like ?", "李%").Find(&employee) //查询姓李的fmt.Println(employee)myDB.Not("name like ?", "李%").Find(&employee) //查询第一条不是姓李的fmt.Println(employee)myDB.Not("name like ?", "李%").Or("age>20").Find(&employeeList) //用Where表示andfor _, value := range employeeList {data, _ := json.Marshal(value)fmt.Println(string(data))}employeeList = []Employee{}myDB.Not("name like ?", "李%").Where("age>20").Find(&employeeList) //用Where表示andfor _, value := range employeeList {data, _ := json.Marshal(value)fmt.Println(string(data))}//selectemployeeList = []Employee{}employeeList1 := []Employee1{}myDB.Select("name", "age").Find(&employeeList).Scan(&employeeList1)for _, value := range employeeList1 {data, _ := json.Marshal(value)fmt.Println(string(data))}//排序employeeList = []Employee{}myDB.Order("age desc").Find(&employeeList)for _, value := range employeeList {data, _ := json.Marshal(value)fmt.Println(string(data))}//分页employeeList = []Employee{}myDB.Limit(4).Offset(0).Order("age desc").Find(&employeeList) //Limit:每页限定记录数，offset:偏移量for _, value := range employeeList {data, _ := json.Marshal(value)fmt.Println(string(data))}//去重var agelist []intmyDB.Table("employees").Select("distinct age").Find(&agelist)for _, value := range agelist {fmt.Println(value)}//分组查询var ageList []int// 查询男生的个数和女生的个数myDB.Table("employees").Select("count(id)").Group("Sex").Scan(&ageList)fmt.Println(ageList)//执行原生sqltype SexGroup struct {Count int `gorm:"column:count(id)"`Sex   boolName  string `gorm:"column:group_concat(name)"`}var sexlist []SexGroupmyDB.Raw("select count(id) ,sex,group_concat(name) from employees group by sex").Scan(&sexlist)for _, value := range sexlist {data, _ := json.Marshal(value)fmt.Println(string(data))}//子查询//select * from students where age > (select avg(age) from students); 原生sqlmyDB.Where("age > (?)", myDB.Model(&Employee{}).Select("avg(age)")).Find(&employee)fmt.Println(employee)//查询引用ScopemyDB.Scopes(Age23).Find(&employee)fmt.Println(employee)
}