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Hook BeforeCreate() error BeforeSave() error AfterCreate() error AfterSave() error } type UpdateUser interface { BeforeUpdate() error BeforeSave() error AfterUpdate() error AfterSave() error } type DeleteUser interface { BeforeDelete() error AfterDelete() 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：
- 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 main import ( "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.DB func 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.Interface mysqlLogger = 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 //Where myDB.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 []Employee myDB.Not("name like ?", "李%").Or("age>20").Find(&employeeList) //用Where表示and for _, 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and for _, 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 string Age int } //select employeeList := []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：
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 []int myDB.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sql type SexGroup struct { Count int `gorm:"column:count(id)"` Sex bool Name string `gorm:"column:group_concat(name)"` } var sexlist []SexGroup myDB.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sql myDB.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 main import ( "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 string Age int } var myDB *gorm.DB func 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.Interface mysqlLogger = 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{} //Where myDB.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and for _, 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and for _, value := range employeeList { data, _ := json.Marshal(value) fmt.Println(string(data)) } //select employeeList = []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 []int myDB.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sql type SexGroup struct { Count int `gorm:"column:count(id)"` Sex bool Name string `gorm:"column:group_concat(name)"` } var sexlist []SexGroup myDB.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sql myDB.Where("age > (?)", myDB.Model(&Employee{}).Select("avg(age)")).Find(&employee) fmt.Println(employee) //查询引用Scope myDB.Scopes(Age23).Find(&employee) fmt.Println(employee) }
