GORM使用以及SQL生成GORM結構體

GORM使用

mysql連接設置連接池數據

import (
  "gorm.io/driver/clickhouse"
  "gorm.io/gorm"
)

func main() {
  dsn := "tcp://localhost:9000?database=gorm&username=gorm&password=gorm&read_timeout=10&write_timeout=20"
  db, err := gorm.Open(clickhouse.Open(dsn), &gorm.Config{})

    // 開啟debug
    db.Debug()
	db.LogMode(true)

   // 維護連接池信息
   sqlDB, err := db.DB()
    // Ping
    sqlDB.Ping()

    // Close
    // sqlDB.Close()

    // 返回數據庫統計信息
    sqlDB.Stats()

    // SetMaxIdleConns 設置空閑連接池中連接的最大數量
    sqlDB.SetMaxIdleConns(10)

    // SetMaxOpenConns 設置打開數據庫連接的最大數量。
    sqlDB.SetMaxOpenConns(100)

    // SetConnMaxLifetime 設置了連接可復用的最大時間。
    sqlDB.SetConnMaxLifetime(time.Hour)

  // Auto Migrate
  db.AutoMigrate(&User{})
  // Set table options
  db.Set("gorm:table_options", "ENGINE=Distributed(cluster, default, hits)").AutoMigrate(&User{})

  // 插入
  db.Create(&user)

  // 查詢
  db.Find(&user, "id = ?", 10)

  // 批量插入
  var users = []User{user1, user2, user3}
  db.Create(&users)
  // ...
}

gorm.Model嵌套

GORM 定義一個 gorm.Model 結構體，其包括字段 ID、CreatedAt、UpdatedAt、DeletedAt.

type User struct {
  gorm.Model
  Name string
}

字段權限控制

GORM 允許您用標簽控制字段級別的權限。這樣您就可以讓一個字段的權限是只讀、只寫、只創建、只更新或者被忽略

type User struct {
  Name string `gorm:"<-:create"` // 允許讀和創建
  Name string `gorm:"<-:update"` // 允許讀和更新
  Name string `gorm:"<-"`        // 允許讀和寫（創建和更新）
  Name string `gorm:"<-:false"`  // 允許讀，禁止寫
  Name string `gorm:"->"`        // 只讀（除非有自定義配置，否則禁止寫）
  Name string `gorm:"->;<-:create"` // 允許讀和寫
  Name string `gorm:"->:false;<-:create"` // 僅創建（禁止從 db 讀）
  Name string `gorm:"-"`  // 通過 struct 讀寫會忽略該字段
}

創建/更新時間追蹤

type User struct {
  CreatedAt time.Time // 在創建時，如果該字段值為零值，則使用當前時間填充
  UpdatedAt int       // 在創建時該字段值為零值或者在更新時，使用當前時間戳秒數填充
  Updated   int64 `gorm:"autoUpdateTime:nano"` // 使用時間戳填納秒數充更新時間
  Updated   int64 `gorm:"autoUpdateTime:milli"` // 使用時間戳毫秒數填充更新時間
  Created   int64 `gorm:"autoCreateTime"`      // 使用時間戳秒數填充創建時間
}

創建

1.)創建指定字段

db.Select("Name", "Age", "CreatedAt").Create(&user)
// INSERT INTO `users` (`name`,`age`,`created_at`) VALUES ("jinzhu", 18, "2020-07-04 11:05:21.775")

2.)忽略部分字段

db.Omit("Name", "Age", "CreatedAt").Create(&user)
// INSERT INTO `users` (`birthday`,`updated_at`) VALUES ("2020-01-01 00:00:00.000", "2020-07-04 11:05:21.775")

3.)批量插入

var users = []User{{Name: "jinzhu1"}, {Name: "jinzhu2"}, {Name: "jinzhu3"}}
db.Create(&users)

var users = []User{{name: "jinzhu_1"}, ...., {Name: "jinzhu_10000"}}
// 數量為 100
db.CreateInBatches(users, 100)

// batch insert from `[]map[string]interface{}{}`
db.Model(&User{}).Create([]map[string]interface{}{
  {"Name": "jinzhu_1", "Age": 18},
  {"Name": "jinzhu_2", "Age": 20},
})

4.）使用默認值

type User struct {
  ID        string `gorm:"default:uuid_generate_v3()"` // db func
  FirstName string `gorm:"default:jone"`
  LastName  string
  Age       uint8
  FullName  string `gorm:"->;type:GENERATED ALWAYS AS (concat(firstname,' ',lastname));default:(-);"`
}

創建鈎子

GORM 允許用戶定義的鈎子有 BeforeSave, BeforeCreate, AfterSave, AfterCreate 創建記錄時將調用這些鈎子方法

func (u *User) BeforeCreate(tx *gorm.DB) (err error) {
  u.UUID = uuid.New()

    if u.Role == "admin" {
        return errors.New("invalid role")
    }
    return
}

// 跳過鈎子
DB.Session(&gorm.Session{SkipHooks: true}).Create(&users)

查詢

1.)查詢單個對象

// 獲取第一條記錄（主鍵升序）
db.First(&user)
// SELECT * FROM users ORDER BY id LIMIT 1;

// 獲取一條記錄，沒有指定排序字段
db.Take(&user)
// SELECT * FROM users LIMIT 1;

// 獲取最后一條記錄（主鍵降序）
db.Last(&user)
// SELECT * FROM users ORDER BY id DESC LIMIT 1;

db.Limit(1).Find(&user)

// 檢查 ErrRecordNotFound 錯誤
errors.Is(result.Error, gorm.ErrRecordNotFound)

2.) 主鍵索引

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);

3.)檢索全部

// 獲取全部記錄
result := db.Find(&users)
// SELECT * FROM users;

4.)條件查詢

// String 條件
// 獲取第一條匹配的記錄
db.Where("name = ?", "jinzhu").First(&user)
// SELECT * FROM users WHERE name = 'jinzhu' ORDER BY id LIMIT 1;

// 獲取全部匹配的記錄
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 & Map 條件
// 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;

// 主鍵切片條件
db.Where([]int64{20, 21, 22}).Find(&users)
// SELECT * FROM users WHERE id IN (20, 21, 22);

// Plain SQL
db.Find(&user, "name = ?", "jinzhu")
// SELECT * FROM users WHERE name = "jinzhu";

// Plain SQL
db.Find(&user, "name = ?", "jinzhu")
// SELECT * FROM users WHERE name = "jinzhu";

// 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;

5.)零值的使用

// 默認忽略零值
db.Where(&User{Name: "jinzhu", Age: 0}).Find(&users)
// SELECT * FROM users WHERE name = "jinzhu";

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

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

6.）分頁查詢

// 通過 -1 消除 Limit 條件
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;

7.）排序分組

// 多個 order
db.Order("age desc").Order("name").Find(&users)
// SELECT * FROM users ORDER BY age desc, name;

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()
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)

8.)多表聯合查詢

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() {
}

工具使用

原生SQL生成GORM結構體
https://sql2gorm.mccode.info/
https://github.com/cascax/sql2gorm
https://juejin.cn/post/6844903508823506958
https://segmentfault.com/a/1190000021441127
https://www.jianshu.com/p/288b9296e4b4