首頁(yè) 猿問(wèn) Golang Gorm 一對(duì)多和一對(duì)一

Golang Gorm 一對(duì)多和一對(duì)一

Go

SMILET 2021-12-20 15:17:46

我正在嘗試通過(guò)構(gòu)建一個(gè)小原型訂單管理應(yīng)用程序來(lái)學(xué)習(xí) Go 和 Gorm。數(shù)據(jù)庫(kù)是 MySQL。通過(guò)簡(jiǎn)單的查詢，Gorm 表現(xiàn)出色。然而，當(dāng)試圖獲得一個(gè)涉及一對(duì)多組合和一對(duì)一關(guān)系的結(jié)果集時(shí)，Gorm 似乎達(dá)不到要求。毫無(wú)疑問(wèn)，實(shí)際上是我缺乏了解。我似乎無(wú)法找到任何關(guān)于我想要完成的工作的在線示例。任何幫助將不勝感激。去結(jié)構(gòu)// Ordertype Order struct { gorm.Model Status string OrderItems []OrderItem}// Order line itemtype OrderItem struct { gorm.Model OrderID uint ItemID uint Item Item Quantity int}// Producttype Item struct { gorm.Model ItemName string Amount float32}數(shù)據(jù)庫(kù)表ordersid | status 1 | pendingorder_itemsid | order_id | item_id | quantity 1 | 1 | 1 | 1 2 | 1 | 2 | 4itemsid | item_name | amount 1 | Go Mug | 12.49 2 | Go Keychain | 6.95 3 | Go T-Shirt | 17.99當(dāng)前查詢order := &Order if err := db.Where("id = ? and status = ?", reqOrder.id, "pending").First(&order).Error; err != nil { fmt.Printf(err.Error())}db.Model(&order).Association("OrderItems").Find(&order.OrderItems)結(jié)果（gorm 進(jìn)行 2 db 查詢）order == Order { id: 1, status: pending, OrderItems[]: { { ID: 1, OrderID: 1, ItemID: 1, Item: nil, Quantity: 1, }, { ID: 2, OrderID: 1, ItemID: 2, Item: nil, Quantity: 4, } }替代查詢order := &Orderdb.Where("id = ? and status = ?", reqOrder.id, "cart").Preload("OrderItems").Preload("OrderItems.Item").First(&order)結(jié)果（gorm 進(jìn)行 3 db 查詢）order == Order { id: 1, status: pending, OrderItems[]: { { ID: 1, OrderID: 1, ItemID: 1, Item: { ID: 1, ItemName: Go Mug, Amount: 12.49, } Quantity: 1, }, { ID: 2, OrderID: 1, ItemID: 2, Item: { ID: 2, ItemName: Go Keychain, Amount: 6.95, }, Quantity: 4, } }理想的結(jié)果上面的“替代查詢”產(chǎn)生了理想的查詢結(jié)果。但是，Gorm 進(jìn)行了 3 個(gè)單獨(dú)的數(shù)據(jù)庫(kù)查詢來(lái)實(shí)現(xiàn)此目的。理想情況下，使用 1 個(gè)（或 2 個(gè)）數(shù)據(jù)庫(kù)查詢可以獲得相同的結(jié)果。這可以通過(guò)幾個(gè)連接在 MySQL 中完成。Gorm 允許連接。但是，我希望利用 Gorm 的一些關(guān)系魔法。謝謝一堆！

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2 回答

慕容708150

TA貢獻(xiàn)1831條經(jīng)驗(yàn) 獲得超4個(gè)贊

如本期所述，gorm 并非旨在使用連接來(lái)預(yù)加載其他結(jié)構(gòu)值。如果您想繼續(xù)使用 gorm 并且有能力使用連接加載值，則必須使用gorm 中公開(kāi)的SQL Builder，并編寫一些代碼來(lái)掃描所需的值。

如果必須考慮許多表，這將變得繁重。如果xorm可用作選項(xiàng)，則它們支持加載結(jié)構(gòu)值。在查找項(xiàng)目符號(hào)下描述，這里。

注意：我沒(méi)有掃描所有字段，只是足以理解這一點(diǎn)。

示例：

package main

import (

"log"

"github.com/jinzhu/gorm"

_ "github.com/jinzhu/gorm/dialects/sqlite"

"github.com/kylelemons/godebug/pretty"

)

// Order

type Order struct {

gorm.Model

Status string

OrderItems []OrderItem

}

// Order line item

type OrderItem struct {

gorm.Model

OrderID uint

ItemID uint

Item Item

Quantity int

}

// Product

type Item struct {

gorm.Model

ItemName string

Amount float32

}

var (

items = []Item{

{ItemName: "Go Mug", Amount: 12.49},

{ItemName: "Go Keychain", Amount: 6.95},

{ItemName: "Go Tshirt", Amount: 17.99},

}

)

func main() {

db, err := gorm.Open("sqlite3", "/tmp/gorm.db")

db.LogMode(true)

if err != nil {

log.Panic(err)

}

defer db.Close()

// Migrate the schema

db.AutoMigrate(&OrderItem{}, &Order{}, &Item{})

// Create Items

for index := range items {

db.Create(&items[index])

}

order := Order{Status: "pending"}

db.Create(&order)

item1 := OrderItem{OrderID: order.ID, ItemID: items[0].ID, Quantity: 1}

item2 := OrderItem{OrderID: order.ID, ItemID: items[1].ID, Quantity: 4}

db.Create(&item1)

db.Create(&item2)

// Query with joins

rows, err := db.Table("orders").Where("orders.id = ? and status = ?", order.ID, "pending").

Joins("Join order_items on order_items.order_id = orders.id").

Joins("Join items on items.id = order_items.id").

Select("orders.id, orders.status, order_items.order_id, order_items.item_id, order_items.quantity" +

", items.item_name, items.amount").Rows()

if err != nil {

log.Panic(err)

}

defer rows.Close()

// Values to load into

newOrder := &Order{}

newOrder.OrderItems = make([]OrderItem, 0)

for rows.Next() {

orderItem := OrderItem{}

item := Item{}

err = rows.Scan(&newOrder.ID, &newOrder.Status, &orderItem.OrderID, &orderItem.ItemID, &orderItem.Quantity, &item.ItemName, &item.Amount)

if err != nil {

log.Panic(err)

}

orderItem.Item = item

newOrder.OrderItems = append(newOrder.OrderItems, orderItem)

}

log.Print(pretty.Sprint(newOrder))

}

輸出：

/tmp/main.go.go:55)

[2018-06-18 18:33:59] [0.74ms] INSERT INTO "items" ("created_at","updated_at","deleted_at","item_name","amount") VALUES ('2018-06-18 18:33:59','2018-06-18 18:33:59',NULL,'Go Mug','12.49')