目錄
Gorm查詢
一般查詢
// 根據主鍵查詢第一條記錄
db.First(&user)
//// SELECT * FROM users ORDER BY id LIMIT 1;
// 隨機獲取一條記錄
db.Take(&user)
//// SELECT * FROM users LIMIT 1;
// 根據主鍵查詢最后一條記錄
db.Last(&user)
//// SELECT * FROM users ORDER BY id DESC LIMIT 1;
// 查詢所有的記錄
db.Find(&users)
//// SELECT * FROM users;
// 查詢指定的某條記錄(僅當主鍵為整型時可用)
db.First(&user, 10)
//// SELECT * FROM users WHERE id = 10;
package main
import (
"database/sql"
"fmt"
"github.com/jinzhu/gorm"
_ "github.com/jinzhu/gorm/dialects/mysql"
)
//1. 定義模型
type User struct {
ID int64
//Name *string `gorm:"default:'zisefeizhu'"`
Name sql.NullString `gorm:"default:'zisefeizhu'"`
Age byte
}
func main() {
//2. 連接Mysql數據庫
db, err := gorm.Open("mysql","root:123456@tcp(127.0.0.1:3306)/db?charset=utf8mb4&parseTime=True&loc=Local")
if err != nil {
panic(err)
}
defer db.Close()
//3. 把模型與數據庫中的表對應起來
db.AutoMigrate(&User{})
//4. 創建結構體實例
//u := User{Name: sql.NullString{"", false}, Age: 60}
//fmt.Println(db.NewRecord(&u)) // 主鍵為空返回`true`
//db.Debug().Create(&u) // 在數據庫中創建一條user記錄
//fmt.Println(db.NewRecord(u)) // 創建`user`后返回`false`
//查詢
//var user User //聲明模型結構體變量類型user (文件夾A)
//db.First(&user) //（文件夾B）
//user:main.User{ID:1, Name:sql.NullString{String:"zisefeizhu", Valid:true}, Age:0x1e}
user := new(User)
db.First(user)
fmt.Printf("user:%#v\n",user)
//user:&main.User{ID:1, Name:sql.NullString{String:"zisefeizhu", Valid:true}, Age:0x1e}
//查詢所有記錄
var users []User
//users := make([]User, 10)
db.Find(&users)
fmt.Printf("user:%#v\n",users)
}
where條件
普通SQL查詢
/ Get first matched record
db.Where("name = ?", "jinzhu").First(&user)
// SELECT * FROM users WHERE name = 'jinzhu' limit 1;
// Get all matched records
db.Where("name = ?", "jinzhu").Find(&users)
// SELECT * FROM users WHERE name = 'jinzhu';
// <>
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';
//查詢where記錄
var users []User
db.Where("name = ?", "zisefeizhu ").Find(&users)
fmt.Printf("user:%#v\n",users)
Struch & Map 查詢
// Struct
db.Where(&User{Name: "jinzhu", Age: 20}).First(&user)
// SELECT * FROM users WHERE name = "jinzhu" AND age = 20 LIMIT 1;
// Map
db.Where(map[string]interface{}{"name": "jinzhu", "age": 20}).Find(&users)
// SELECT * FROM users WHERE name = "jinzhu" AND age = 20;
// 主鍵的切片
db.Where([]int64{20, 21, 22}).Find(&users)
//SELECT * FROM users WHERE id IN (20, 21, 22);
注意：當通過結構體進行查詢時，GORM將會只通過非零值字段查詢，這意味着如果你的字段值為0，''，false或者其他零值時，將不會被用於構建查詢條件。
db.Where(&User{Name: "jinzhu", Age: 0}).Find(&users)
// SELECT * FROM users WHERE name = "jinzhu";
可以使用指針或實現 Scanner/Valuer 接口來避免這個問題
// 使用指針
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 實現了 Scanner/Valuer 接口
}
Not條件
作用與 Where 類似的情形
db.Not("name", "jinzhu").First(&user)
//// SELECT * FROM users WHERE name <> "jinzhu" LIMIT 1;
// Not In
db.Not("name", []string{"jinzhu", "jinzhu 2"}).Find(&users)
//// SELECT * FROM users WHERE name NOT IN ("jinzhu", "jinzhu 2");
// Not In slice of primary keys
db.Not([]int64{1,2,3}).First(&user)
//// SELECT * FROM users WHERE id NOT IN (1,2,3);
db.Not([]int64{}).First(&user)
//// SELECT * FROM users;
// Plain SQL
db.Not("name = ?", "jinzhu").First(&user)
//// SELECT * FROM users WHERE NOT(name = "jinzhu");
// Struct
db.Not(User{Name: "jinzhu"}).First(&user)
//// SELECT * FROM users WHERE name <> "jinzhu";
Or條件
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"}).Find(&users)
//// SELECT * FROM users WHERE name = 'jinzhu' OR name = 'jinzhu 2';
// Map
db.Where("name = 'jinzhu'").Or(map[string]interface{}{"name": "jinzhu 2"}).Find(&users)
//// SELECT * FROM users WHERE name = 'jinzhu' OR name = 'jinzhu 2';
內聯條件
作用與Where查詢類似，當內聯條件與多個立即執行方法一起使用時, 內聯條件不會傳遞給后面的立即執行方法。
// 根據主鍵獲取記錄 (只適用於整形主鍵)
db.First(&user, 23)
//// SELECT * FROM users WHERE id = 23 LIMIT 1;
// 根據主鍵獲取記錄, 如果它是一個非整形主鍵
db.First(&user, "id = ?", "string_primary_key")
//// SELECT * FROM users WHERE id = 'string_primary_key' LIMIT 1;
// 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;
額外查詢選項
// 為查詢 SQL 添加額外的 SQL 操作
db.Set("gorm:query_option", "FOR UPDATE").First(&user, 10)
//// SELECT * FROM users WHERE id = 10 FOR UPDATE;
FirstOrInit
獲取匹配的第一條記錄，否則根據給定的條件初始化一個新的對象 (僅支持 struct 和 map 條件)
//查詢FirstOrInit記錄
var user User
db.FirstOrInit(&user,User{Name: "小王子"})
fmt.Printf("user:%#v\n",user)
//user:main.User{ID:0, Name:"小王子", Age:0x15}
Attrs
如果記錄未找到，將使用參數初始化 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}
Assign
不管記錄是否找到，都將參數賦值給 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}
FirstOrCreate
獲取匹配的第一條記錄, 否則根據給定的條件創建一個新的記錄 (僅支持 struct 和 map 條件)
// 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"}
Attrs
如果記錄未找到，將使用參數創建 struct 和記錄.
// 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}
Assign
不管記錄是否找到，都將參數賦值給 struct 並保存至數據庫.
// 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}
高級查詢
子查詢
基於 *gorm.expr 的子查詢
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')));
選擇字段
Select，指定你想從數據庫中檢索出的字段，默認會選擇全部字段。
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，指定從數據庫中檢索出記錄的順序。設置第二個參數 reorder 為 true ，可以覆蓋前面定義的排序條件。
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;
// 覆蓋排序
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)
數量
Limit，指定從數據庫檢索出的最大記錄數。
db.Limit(3).Find(&users)
//// SELECT * FROM users LIMIT 3;
// -1 取消 Limit 條件
db.Limit(10).Find(&users1).Limit(-1).Find(&users2)
//// SELECT * FROM users LIMIT 10; (users1)
//// SELECT * FROM users; (users2)
偏移
Offset，指定開始返回記錄前要跳過的記錄數。
db.Offset(3).Find(&users)
//// SELECT * FROM users OFFSET 3;
// -1 取消 Offset 條件
db.Offset(10).Find(&users1).Offset(-1).Find(&users2)
//// SELECT * FROM users OFFSET 10; (users1)
//// SELECT * FROM users; (users2)
總數
Count，該 model 能獲取的記錄總數
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 必須是鏈式查詢的最后一個操作 ，因為它會覆蓋前面的 SELECT，但如果里面使用了 count 時不會覆蓋
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將多條結果掃描進事先准備好的結構體切片中
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)
連接
Joins，指定連接條件
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)
// 多連接及參數
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，查詢 model 中的一個列作為切片，如果您想要查詢多個列，您應該使用 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)
// 想查詢多個字段？ 這樣做：
db.Select("name, age").Find(&users)
掃描
Scan，掃描結果至一個 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)
鏈式操作相關
鏈式操作
Method Chaining，Gorm 實現了鏈式操作接口，所以你可以把代碼寫成這樣：
// 創建一個查詢
tx := db.Where("name = ?", "jinzhu")
// 添加更多條件
if someCondition {
tx = tx.Where("age = ?", 20)
} else {
tx = tx.Where("age = ?", 30)
}
if yetAnotherCondition {
tx = tx.Where("active = ?", 1)
}
在調用立即執行方法前不會生成Query語句，借助這個特性你可以創建一個函數來處理一些通用邏輯。
立即執行方法
Immediate methods ，立即執行方法是指那些會立即生成SQL語句並發送到數據庫的方法, 他們一般是CRUD方法，比如：
Create, First, Find, Take, Save, UpdateXXX, Delete, Scan, Row, Rows…
這有一個基於上面鏈式方法代碼的立即執行方法的例子
tx.Find(&user)
生成的SQL語句如下：
SELECT * FROM users where name = 'jinzhu' AND age = 30 AND active = 1;
范圍
Scopes，Scope是建立在鏈式操作的基礎之上的。
基於它，你可以抽取一些通用邏輯，寫出更多可重用的函數庫。
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)
// 查找所有金額大於 1000 的信用卡訂單
db.Scopes(AmountGreaterThan1000, PaidWithCod).Find(&orders)
// 查找所有金額大於 1000 的 COD 訂單
db.Scopes(AmountGreaterThan1000, OrderStatus([]string{"paid", "shipped"})).Find(&orders)
// 查找所有金額大於 1000 且已付款或者已發貨的訂單
多個立即執行方法
Multiple Immediate Methods，在 GORM 中使用多個立即執行方法時，后一個立即執行方法會復用前一個立即執行方法的條件 (不包括內聯條件) 。
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%'