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小能豆

golang GORM和Gin无法创建具有关联的对象

go

我使用 GORM 进行 ORM 并通过 Golang API 与我的数据库进行通信。

但是，对于创建与数据库关联的实体，它失败了，代码为 ( DB.Create(&data)) ：

2023/11/01 20:44:14 [Recovery] 2023/11/01 - 20:44:14 panic recovered:
POST /v1/product/products HTTP/1.1
Host: localhost:8080
Accept: */*
Content-Length: 589
Content-Type: application/json
User-Agent: curl/8.4.0


runtime error: invalid memory address or nil pointer dereference
/usr/lib/go/src/runtime/panic.go:261 (0x452d97)
        panicmem: panic(memoryError)
/usr/lib/go/src/runtime/signal_unix.go:861 (0x452d65)
        sigpanic: panicmem()
/home/grimm/go/pkg/mod/gorm.io/gorm@v1.25.5/finisher_api.go:18 (0x926e7c)
        (*DB).Create: if db.CreateBatchSize > 0 {
/home/grimm/Documents/beeskill/website/back_end/API_website/main.go:122 (0x99cfab)
        CreatingProduct: DB.Create(&data)
/home/grimm/go/pkg/mod/github.com/gin-gonic/gin@v1.9.1/context.go:174 (0x8c9ad9)
        (*Context).Next: c.handlers[c.index](c)
/home/grimm/go/pkg/mod/github.com/gin-gonic/gin@v1.9.1/recovery.go:102 (0x8c9ac7)
        CustomRecoveryWithWriter.func1: c.Next()
/home/grimm/go/pkg/mod/github.com/gin-gonic/gin@v1.9.1/context.go:174 (0x8c8c7d)
        (*Context).Next: c.handlers[c.index](c)
/home/grimm/go/pkg/mod/github.com/gin-gonic/gin@v1.9.1/logger.go:240 (0x8c8c4c)
        LoggerWithConfig.func1: c.Next()
/home/grimm/go/pkg/mod/github.com/gin-gonic/gin@v1.9.1/context.go:174 (0x8c7d3a)
        (*Context).Next: c.handlers[c.index](c)
/home/grimm/go/pkg/mod/github.com/gin-gonic/gin@v1.9.1/gin.go:620 (0x8c79cd)
        (*Engine).handleHTTPRequest: c.Next()
/home/grimm/go/pkg/mod/github.com/gin-gonic/gin@v1.9.1/gin.go:576 (0x8c74fc)
        (*Engine).ServeHTTP: engine.handleHTTPRequest(c)
/usr/lib/go/src/net/http/server.go:2938 (0x6a35ed)
        serverHandler.ServeHTTP: handler.ServeHTTP(rw, req)
/usr/lib/go/src/net/http/server.go:2009 (0x69f4d3)
        (*conn).serve: serverHandler{c.server}.ServeHTTP(w, w.req)
/usr/lib/go/src/runtime/asm_amd64.s:1650 (0x46ed20)
        goexit: BYTE    $0x90   // NOP

使用的代码：

package main

import (
    "net/http"

    "github.com/gin-gonic/gin"
    "gorm.io/driver/sqlite"
    "gorm.io/gorm"
)

type CategoryProduct struct {
    gorm.Model
    Title       string `json:"title" gorm:"not null"`
    Description string `json:"description"`
}

type CreateCategoryProduct struct {
    gorm.Model
    Title       string `json:"title" binding:"required"`
    Description string `json:"description" binding:"required"`
}

// --------------------------------------------------------
// --------------------------------------------------------
// --------------------------------------------------------
// --------------------------------------------------------
// --------------------------------------------------------
type PriceYearProduct struct {
    gorm.Model
    Price       float64 `json:"price" gorm:"not null"`
    Description string  `json:"description"`
}

type CreatePriceYearProduct struct {
    gorm.Model
    Price       float64 `json:"price" binding:"required"`
    Description string  `json:"description" binding:"required"`
}

// --------------------------------------------------------
// --------------------------------------------------------
// --------------------------------------------------------
// --------------------------------------------------------
// --------------------------------------------------------
type PriceMounthProduct struct {
    gorm.Model
    Price       float64 `json:"price" gorm:"not null"`
    Description string  `json:"description"`
}

type CreatePriceMounthProduct struct {
    gorm.Model
    Price       float64 `json:"price" binding:"required"`
    Description string  `json:"description" binding:"required"`
}

// --------------------------------------------------------
// --------------------------------------------------------
// --------------------------------------------------------
// --------------------------------------------------------
// --------------------------------------------------------
type Product struct {
    gorm.Model
    Name               string             `json:"name" gorm:"not null"`
    Description        string             `json:"description" gorm:"not null"`
    PriceMounthProduct PriceMounthProduct `json:"pricemounth"`
    PriceYearProduct   PriceYearProduct   `json:"priceyear"`
    CategoryProduct    CategoryProduct    `json:"category"`
}

type CreateProduct struct {
    gorm.Model
    Name               string             `json:"name" binding:"required"`
    Description        string             `json:"description" binding:"required"`
    PriceMounthProduct PriceMounthProduct `json:"pricemounth" binding:"required"`
    PriceYearProduct   PriceYearProduct   `json:"priceyear" binding:"required"`
    CategoryProduct    CategoryProduct    `json:"category" binding:"required"`
}

var DB *gorm.DB

func ConnectDatabase() {

    database, err := gorm.Open(sqlite.Open("test.db"), &gorm.Config{})

    if err != nil {
        panic("Failed to connect to database!")
    }
    // For the product and dependancies of them
    err = database.AutoMigrate(&CategoryProduct{}, &PriceYearProduct{}, &PriceMounthProduct{})
    if err != nil {
        return
    }
    err = database.AutoMigrate(&Product{})
    if err != nil {
        return
    }

    DB = database
}

// POST /v1/products
// Create a product
func CreatingProduct(c *gin.Context) {
    // Validate input
    var input CreateProduct
    if err := c.ShouldBindJSON(&input); err != nil {
        c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
        return
    }

    data := Product{
        Name:               input.Name,
        Description:        input.Description,
        PriceYearProduct:   input.PriceYearProduct,
        PriceMounthProduct: input.PriceMounthProduct,
        CategoryProduct:    input.CategoryProduct,
    }
    DB.Create(&data)

    c.JSON(http.StatusOK, gin.H{"data": data})

}

func Routes() {
    var router = gin.Default()

    v1 := router.Group("/v1")
    {
        //Product CRUD
        product := v1.Group("/product")
        product.POST("/products", CreatingProduct)

    }

    err := router.Run(":8080")
    if err != nil {
        return
    }
}

func main() {
    ConnectDatabase()
    Routes()

}

以及用于 POST 一些数据的curl 命令：

curl http://localhost:8080/v1/product/products --request "POST" --header "Content-Type: application/json" --data @file.json

file.json 的内容：

{
    "name": "airplane simulation",
    "description": "airplane simulation for everybody, childrens to adults.",
    "priceyear": {
      "price": 44.99,
      "description": "pay for a year to access on irplane simulation for everybody, childrens to adults."
    },
    "pricemounth": {
      "price": 4.99,
      "description": "pay for a mounth to access on irplane simulation for everybody, childrens to adults."
    },
    "category": {
      "title": "Airplane",
      "description": "Information cataegorized on airplane."
    }
}

我查看了官方文档，但没有更多信息…尝试使用创建时的变量进行调试，但一切似乎都很好…


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2023-11-02

共1个答案

小能豆

根据你提供的代码和错误信息，问题出现在创建Product实体时。具体来说，你在创建Product时，使用了CreateProduct结构体的字段，但你的CreateProduct结构体定义了嵌套的结构体字段，例如PriceYearProduct，PriceMounthProduct，和CategoryProduct。

GORM 默认情况下不会自动为你的嵌套结构体创建关联关系，所以当你调用DB.Create(&data)时，它尝试将嵌套的结构体保存为独立的记录，但由于没有提供外键等信息，导致出现错误。这可能是导致空指针异常的原因。

要解决这个问题，你可以告诉GORM如何正确处理这些嵌套结构体。你可以使用Preload函数来预加载嵌套结构体并将其与Product一起保存，如下所示：

data := CreateProduct{
    Name:               input.Name,
    Description:        input.Description,
    PriceYearProduct:   input.PriceYearProduct,
    PriceMounthProduct: input.PriceMounthProduct,
    CategoryProduct:    input.CategoryProduct,
}
DB.Preload("PriceYearProduct").Preload("PriceMounthProduct").Preload("CategoryProduct").Create(&data)

这将告诉GORM在创建Product记录时一并创建并保存关联的PriceYearProduct，PriceMounthProduct和CategoryProduct。

另外，你的数据模型和路由处理函数可能需要进一步的改进，以适应你的需求。确保你的路由处理函数正确处理错误情况，比如数据库连接失败或验证错误。

最后，为了更好地调试问题，你可以使用错误处理机制来获取GORM的错误信息，以便更清楚地了解出现问题的具体原因。例如，你可以使用Error方法来获取GORM的错误信息并将其记录下来，以便进一步排查问题。

2023-11-02