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阿里云虛擬主機(jī)怎么建設(shè)網(wǎng)站,seopeix,承德網(wǎng)站制作公司優(yōu)選網(wǎng)十科技,建網(wǎng)站找我GORM 指南 | GORM - The fantastic ORM library for Golang, aims to be developer friendly. 一對(duì)多入門比如要開發(fā)cmdb的系統(tǒng)，無(wú)論是硬件還是軟件。硬件對(duì)應(yīng)的就是對(duì)應(yīng)的哪個(gè)開發(fā)在用?；蛘叻?wù)對(duì)應(yīng)的是哪個(gè)業(yè)務(wù)模塊在使用，或者應(yīng)用誰(shuí)在使用。那么這…

GORM 指南 | GORM - The fantastic ORM library for Golang, aims to be developer friendly.

一對(duì)多入門

比如要開發(fā)cmdb的系統(tǒng)，無(wú)論是硬件還是軟件。硬件對(duì)應(yīng)的就是對(duì)應(yīng)的哪個(gè)開發(fā)在用?；蛘叻?wù)對(duì)應(yīng)的是哪個(gè)業(yè)務(wù)模塊在使用，或者應(yīng)用誰(shuí)在使用。那么這就是一對(duì)多的關(guān)系。

has many介紹

has many 關(guān)聯(lián)就是創(chuàng)建和另一個(gè)模型的一對(duì)多關(guān)系（數(shù)據(jù)庫(kù)里面是一對(duì)多，然后struct里面也是一對(duì)多）
例如，例如每一個(gè)用戶都擁有多張信用卡，這樣就是生活中一個(gè)簡(jiǎn)單的一對(duì)多關(guān)系

在設(shè)計(jì)表的時(shí)候不可能將所有的信息都放在一個(gè)表里面，那么表就會(huì)非常非常的寬。這樣字段就會(huì)非常的多，性能就會(huì)受到影響。

在設(shè)計(jì)的時(shí)候這里其實(shí)就可以設(shè)置為兩張表。一個(gè)是用戶的詳情表和信用卡的詳情表，用戶表里面加上卡的id和他做一個(gè)關(guān)聯(lián)，那么這就是一對(duì)多的關(guān)系。

當(dāng)一個(gè)數(shù)據(jù)庫(kù)存儲(chǔ)了很多數(shù)據(jù)的時(shí)候就需要分庫(kù)分表，上面也類似，將一張表分為兩張表。

creditcar的外鍵是userid。

package mainimport ("gorm.io/driver/mysql""gorm.io/gorm"
)type User struct {gorm.Model  //默認(rèn)創(chuàng)建三個(gè)時(shí)間字段和一個(gè)id字段，create_at update_at delete_at這樣可以知道創(chuàng)建時(shí)間/更新時(shí)間/刪除時(shí)間CreditCards []*CreditCard66
}//用戶有多張信用卡，UserID是外鍵
type CreditCard struct {gorm.ModelNumber   stringUserId int //默認(rèn)會(huì)在CreditCard表中生成User66Id字段作為與user表關(guān)聯(lián)的外鍵id//默認(rèn)會(huì)在CreditCard表中生成UserID字段作為與User表關(guān)聯(lián)的外鍵ID 
}func main() {dsn := "root:7PXjAkY!&nlR@tcp(192.168.11.128:3306)/test_db?charset=utf8mb4&parseTime=True&loc=Local"db, _ := gorm.Open(mysql.Open(dsn66), &gorm.Config{})db.AutoMigrate(User{}, CreditCard{})
}

mysql> show tables;
+-------------------+
| Tables_in_test_db |
+-------------------+
| credit_cards      |
| users             |
+-------------------+
2 rows in set (0.00 sec)mysql> desc users;
+------------+-----------------+------+-----+---------+----------------+
| Field      | Type            | Null | Key | Default | Extra          |
+------------+-----------------+------+-----+---------+----------------+
| id         | bigint unsigned | NO   | PRI | NULL    | auto_increment |
| created_at | datetime(3)     | YES  |     | NULL    |                |
| updated_at | datetime(3)     | YES  |     | NULL    |                |
| deleted_at | datetime(3)     | YES  | MUL | NULL    |                |
+------------+-----------------+------+-----+---------+----------------+mysql> desc credit_cards;
+------------+-----------------+------+-----+---------+----------------+
| Field      | Type            | Null | Key | Default | Extra          |
+------------+-----------------+------+-----+---------+----------------+
| id         | bigint unsigned | NO   | PRI | NULL    | auto_increment |
| created_at | datetime(3)     | YES  |     | NULL    |                |
| updated_at | datetime(3)     | YES  |     | NULL    |                |
| deleted_at | datetime(3)     | YES  | MUL | NULL    |                |
| number     | bigint          | YES  |     | NULL    |                |
| user_id    | bigint unsigned | YES  | MUL | NULL    |                |
+------------+-----------------+------+-----+---------+----------------+mysql> drop table users;
ERROR 3730 (HY000): Cannot drop table 'users' referenced by a foreign key constraint 'fk_users_credit_cards' on table 'credit_cards'.

?二? 外鍵

為了定義一對(duì)多關(guān)系，外鍵是必須存在的，默認(rèn)外鍵的名字是所有者類型的名字加上它的主鍵

(UserId) 。就像上面的例子，為了定義一個(gè)屬于User 的模型，外鍵就應(yīng)該為 UserID 。

使用其他的字段名作為外鍵，你可以通過 foreignkey 來(lái)定制它，例如 :

type User struct{gorm.ModelCreditCards []CreditCard `gorm:"foreignKey:UserRefer"`
}type CreditCard struct{gorm.ModelNumber??stringUserRefer uint
}

`gorm:"foreignKey:UserRefer"` 可以使用這個(gè)字段來(lái)去改它的外鍵。

import ("gorm.io/driver/mysql""gorm.io/gorm"
)type User struct {gorm.ModelCreditCards []*CreditCard `gorm:"foreignKey:UserRefer"`
}type CreditCard struct {gorm.ModelNumber    intUserRefer int  
}func main() {dsn6 := "root:7PXjAkY!&nlR@tcp(192.168.11.128:3306)/test_db?charset=utf8mb4&parseTime=True&loc=Local"db, _ := gorm.Open(mysql.Open(dsn6), &gorm.Config{})db.AutoMigrate(&User{}, &CreditCard{})
}mysql> desc users;
+------------+-----------------+------+-----+---------+----------------+
| Field      | Type            | Null | Key | Default | Extra          |
+------------+-----------------+------+-----+---------+----------------+
| id         | bigint unsigned | NO   | PRI | NULL    | auto_increment |
| created_at | datetime(3)     | YES  |     | NULL    |                |
| updated_at | datetime(3)     | YES  |     | NULL    |                |
| deleted_at | datetime(3)     | YES  | MUL | NULL    |                |
+------------+-----------------+------+-----+---------+----------------+mysql> desc credit_cards;
+------------+-----------------+------+-----+---------+----------------+
| Field      | Type            | Null | Key | Default | Extra          |
+------------+-----------------+------+-----+---------+----------------+
| id         | bigint unsigned | NO   | PRI | NULL    | auto_increment |
| created_at | datetime(3)     | YES  |     | NULL    |                |
| updated_at | datetime(3)     | YES  |     | NULL    |                |
| deleted_at | datetime(3)     | YES  | MUL | NULL    |                |
| number     | bigint          | YES  |     | NULL    |                |
| user_refer | bigint unsigned | YES  | MUL | NULL    |                |
+------------+-----------------+------+-----+---------+----------------+mysql> drop tables users;
ERROR 3730 (HY000): Cannot drop table 'users' referenced by a foreign key constraint 'fk_users_credit_cards' on table 'credit_cards'.

一般不推薦使用這種方式，還是推薦使用Userid的方式。

三外鍵關(guān)聯(lián)

GORM 通常使用所有者的主鍵作為外鍵的值，在上面的例子中，它就是 User 的 ID 。當(dāng)你分配信用卡給一個(gè)用戶，GORM 將保存用戶 ID 到信用卡表的 UserID 字段中。你能通過association_foreignkey來(lái)改變它。

type User struct {gorm.ModelMemberNumber string
// 默認(rèn)CreditCard會(huì)使用User表的Id作為外鍵，association_foreignkey:MemberNumber
// 指定使用MemberNumber 作為外鍵關(guān)聯(lián)
CreditCards []CreditCard
`gorm:"foreignkey:UserMemberNumber;association_foreignkey:MemberNumber"`
}type CreditCard struct {gorm.ModelNumber stringUserMemberNumber string
}

其實(shí)就是creditcard外鍵UserMemberNumber直接去找user的?MemberNumber。

上面其實(shí)也就是改變了外鍵的默認(rèn)值，默認(rèn)外鍵是Userid，那么現(xiàn)在變?yōu)榱薓emberNumber。

一般使用默認(rèn)id的外鍵就能夠覆蓋很多場(chǎng)景，上面這種只是舉例。

package mainimport ("gorm.io/driver/mysql""gorm.io/gorm"
)type User struct {gorm.ModelMemberNumber stringCreditCards  []*CreditCard `gorm:"foreignKey:UserMemberNumber;association_foreignKey:MemberNumber"`
}type CreditCard struct {gorm.ModelNumber           intUserMemberNumber string
}func main() {dsn6 := "root:7PXjAkY!&nlR@tcp(192.168.11.128:3306)/test_db?charset=utf8mb4&parseTime=True&loc=Local"db, _ := gorm.Open(mysql.Open(dsn6), &gorm.Config{})db.AutoMigrate(&User{}, &CreditCard{})
}mysql> desc users;
+---------------+-----------------+------+-----+---------+----------------+
| Field         | Type            | Null | Key | Default | Extra          |
+---------------+-----------------+------+-----+---------+----------------+
| id            | bigint unsigned | NO   | PRI | NULL    | auto_increment |
| created_at    | datetime(3)     | YES  |     | NULL    |                |
| updated_at    | datetime(3)     | YES  |     | NULL    |                |
| deleted_at    | datetime(3)     | YES  | MUL | NULL    |                |
| member_number | longtext        | YES  |     | NULL    |                |
+---------------+-----------------+------+-----+---------+----------------+mysql> desc credit_cards;
+--------------------+-----------------+------+-----+---------+----------------+
| Field              | Type            | Null | Key | Default | Extra          |
+--------------------+-----------------+------+-----+---------+----------------+
| id                 | bigint unsigned | NO   | PRI | NULL    | auto_increment |
| created_at         | datetime(3)     | YES  |     | NULL    |                |
| updated_at         | datetime(3)     | YES  |     | NULL    |                |
| deleted_at         | datetime(3)     | YES  | MUL | NULL    |                |
| number             | bigint          | YES  |     | NULL    |                |
| user_member_number | bigint unsigned | YES  | MUL | NULL    |                |
+--------------------+-----------------+------+-----+---------+----------------+

四創(chuàng)建一對(duì)多表

1. 表結(jié)構(gòu)定義

/*
constraint:OnUpdate:CASCADE 【當(dāng)User表更新，也會(huì)同步給CreditCards】 // 外鍵約束
OnDelete:SET NULL 【當(dāng)User中數(shù)據(jù)被刪除時(shí)，CreditCard關(guān)聯(lián)設(shè)置為 NULL，不刪除記錄】
*/type User struct {gorm.ModelUsername string `json:"username" gorm:"column:username"`CreditCards []CreditCard `gorm:"constraint:OnUpdate:CASCADE,OnDelete:SET NULL;"`
}type CreditCard struct {gorm.ModelNumber stringUserID uint
}func main() {// 0、連接數(shù)據(jù)庫(kù)dsn := "root:1@tcp(127.0.0.1:3306)/test_db?charset=utf8mb4&parseTime=True&loc=Local"db, _ := gorm.Open(mysql.Open(dsn), &gorm.Config{})// 創(chuàng)建表結(jié)構(gòu)db.AutoMigrate(User{}, CreditCard{})// 1、創(chuàng)建一對(duì)多user := User{Username: "zhangsan",CreditCards: []CreditCard{{Number: "0001"},{Number: "0002"},},
}db.Create(&user)// 2、為已存在用戶添加信用卡u := User{Username: "zhangsan"}db.First(&u)//fmt.Println(u.Username)}

上面如果要查詢的話是沒有去做關(guān)聯(lián)查詢的，只能查到user表相關(guān)的信息，并不能查到creditcard信息。

2. 創(chuàng)建結(jié)果說明

我們沒有指定 foreignkey ，所以會(huì)與 UserID 字段自動(dòng)建立外鍵關(guān)聯(lián)關(guān)系

3. 一對(duì)多Association 查找關(guān)聯(lián) 使用 Association 方法, 需要把把 User 查詢好, 然后根據(jù) User 定義中指定的 AssociationForeignKey 去查找 CreditCard

import ("fmt""gorm.io/driver/mysql""gorm.io/gorm"
)type User struct {gorm.ModelUserName    string       `json:"username" gorm:"column:username"`CreditCards []CreditCard `gorm:"constraint:OnUpdate:CASCADE,OnDelete:SET NULL;"`
}type CreditCard struct {gorm.ModelNumber stringUserID int
}func main() {dsn6 := "root:7PXjAkY!&nlR@tcp(192.168.11.128:3306)/test_db?charset=utf8mb4&parseTime=True&loc=Local"db, _ := gorm.Open(mysql.Open(dsn6), &gorm.Config{})db.AutoMigrate(&User{}, &CreditCard{})/*u := &User{Model:    gorm.Model{},UserName: "lucas",CreditCards: []*CreditCard{{Number: "0001", UserID: 1},{Number: "0002", UserID: 2},},}db.Create(u)*/// 1、查找 用戶名為 lucas 的所有信用卡信息u1 := &User{UserName: "lucas"}// Association必須要先查出User才能關(guān)聯(lián)查詢對(duì)應(yīng)的CreditCarddb.First(u1)db.Model(u1).Association("CreditCards").Find(&u1.CreditCards)fmt.Println(u1)}

追加

package mainimport ("encoding/json""fmt""gorm.io/driver/mysql""gorm.io/gorm"
)type User struct {gorm.ModelUserName    string       `json:"username" gorm:"column:username"`CreditCards []CreditCard `gorm:"constraint:OnUpdate:CASCADE,OnDelete:SET NULL;"`
}type CreditCard struct {gorm.ModelNumber stringUserID int
}func main() {dsn6 := "root:7PXjAkY!&nlR@tcp(192.168.11.128:3306)/test_db?charset=utf8mb4&parseTime=True&loc=Local"db, _ := gorm.Open(mysql.Open(dsn6), &gorm.Config{})db.AutoMigrate(&User{}, &CreditCard{})u := &User{Model:    gorm.Model{},UserName: "lucas",CreditCards: []CreditCard{{Number: "0001", UserID: 0},{Number: "0002", UserID: 1},},}db.Create(u)u1 := &User{UserName: "lucas"}db.First(u1)db.Model(u1).Association("CreditCards").Find(&u1.CreditCards)fmt.Println(u1)db.Model(u1).Association("CreditCards").Append([]CreditCard{{Number: "0008", UserID: 1},})fmt.Println(u1)strUser, _ := json.Marshal(u1)fmt.Println(string(strUser))
}&{{1 2023-04-16 10:48:54.423 +0800 CST 2023-04-16 14:12:45.825 +0800 CST {0001-01-01 00:00:00 +0000 UTC false}} lucas []}&{{1 2023-04-16 10:48:54.423 +0800 CST 2023-04-16 14:15:51.44 +0800 CST {0001-01-01 00:00:00 +0000 UTC false}} lucas [{{17 2023-04-16 14:15:51.445+0800 CST 2023-04-16 14:15:51.445 +0800 CST {0001-01-01 00:00:00 +0000 UTC false}} 0008 1}]}{"ID":1,"CreatedAt":"2023-04-16T10:48:54.423+08:00","UpdatedAt":"2023-04-16T14:15:51.44+08:00","DeletedAt":null,"username":"lucas","CreditCards":[
{"ID":17,"CreatedAt":"2023-04-16T14:15:51.445+08:00","UpdatedAt":"2023-04-16T14:15:51.445+08:00","DeletedAt":null,"Number":"0008","UserID":1}]}

4. 一對(duì)多Preload 預(yù)加載

使用 Preload 方法, 在查詢 User 時(shí)先去獲取 CreditCard 的記錄

和上面associate不一樣，他們兩個(gè)最大的區(qū)別是執(zhí)行的順序是不一樣的，associate是先去獲取user，再去獲取creditcard。

preload是先去獲取creditcard，再去獲取user。

package main
import (
"encoding/json"
"fmt"
"gorm.io/driver/mysql"
"gorm.io/gorm"
)
/*
constraint:OnUpdate:CASCADE 【當(dāng)User表更新，也會(huì)同步給CreditCards】
OnDelete:SET NULL 【當(dāng)User中數(shù)據(jù)被刪除時(shí)，CreditCard關(guān)聯(lián)設(shè)置為 NULL，不刪除記錄】
*/
type User struct {
gorm.Model
Username string `json:"username" gorm:"column:username"`
CreditCards []CreditCard `gorm:"constraint:OnUpdate:CASCADE,OnDelete:SET
NULL;"`
}
type CreditCard struct {
gorm.Model
Number string
UserID uint
}
func main() {
// 0、連接數(shù)據(jù)庫(kù)
dsn := "root:1@tcp(127.0.0.1:3306)/test_db?
charset=utf8mb4&parseTime=True&loc=Local"
db, _ := gorm.Open(mysql.Open(dsn), &gorm.Config{})
// 1、預(yù)加載: 查找 user 時(shí)預(yù)加載相關(guān) CreditCards
//users := User{Username: "zhangsan"} // 只查找張三用戶的信用卡信息
users := []User{}
db.Preload("CreditCards").Find(&users)
查詢結(jié)果[
{
"ID":1,
"username":"zhangsan",
"CreditCards":[
{
"ID":1,
"Number":"0001",
"UserID":1
},
...
]
}
]

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阿里云虛擬主機(jī)怎么建設(shè)網(wǎng)站seopeix

GORM 指南 | GORM - The fantastic ORM library for Golang, aims to be developer friendly.

一對(duì)多入門

?二? 外鍵

三外鍵關(guān)聯(lián)

四創(chuàng)建一對(duì)多表

相關(guān)文章：

中文亚洲精品无码_熟女乱子伦免费_人人超碰人人爱国产_亚洲熟妇女综合网

GORM 指南 | GORM - The fantastic ORM library for Golang, aims to be developer friendly.

一 對(duì)多入門

?二? 外鍵

三 外鍵關(guān)聯(lián)

四 創(chuàng)建一對(duì)多表

相關(guān)文章：

一對(duì)多入門

三外鍵關(guān)聯(lián)

四創(chuàng)建一對(duì)多表