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运行时错误:无效的内存地址或 nil 指针取消引用 (2)

来源:stackoverflow

时间:2024-04-25 23:03:38 266浏览 收藏

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问题内容

我是 go 新手,需要帮助!

在 postgresql 数据库中,我有一个名为 factors 的表。该表有 2 列(factor_idfactor_name)。现在我已成功从 go 应用程序连接到 postgresql 数据库。

当我尝试在控制台中发出基于查询的 get 请求时,我看到错误。

http://localhost:8000/api/factors/?limit=5&offset=1

我哪里出错了?请帮我解决这个问题。

controllers/factors.go

package controllers

import (
    "encoding/json"
    "fmt"
    "net/http"
    "restify/models"
    "restify/utils"
)

var getfactors = func(res http.responsewriter, req *http.request) {
    data := models.factors{}

    err := models.getfactors(&data, req.url.query().get("limit"), req.url.query().get("offset"))
    if err != nil {
        fmt.println(err.error())
        http.error(res, err.error(), 500)
        return
    }

    out, err := json.marshal(data)
    if err != nil {
        fmt.println(err.error())
        http.error(res, err.error(), 501)
        return
    }

    resp := make(map[string]interface{})

    resp["dictionaries"] = string(out)

    utils.respond(res, resp)

}

models/factors.go

package models

import (
    "fmt"
    "restify/database"
)

type factor struct {
    factorid int `json:"factor_id"`
    factorname string `json:"factor_name"`
}

type factors struct {
    array[]factor
}

func getfactors(data *factors, limit string, offset string) error {
    rows, err := database.db.query(`select * from factors order by factor_id limit ` + limit + ` offset ` + offset + `;`)
    if err != nil {
        fmt.println(err)
        return err
    }
    defer rows.close()
    for rows.next() {
        var id int
        var name string
        model := factor{}
        err = rows.scan(&id, &name)
        if err != nil {
            fmt.println(err)
            return err
        }
        model.factorid = id
        model.factorname = name
        data.array = append(data.array, model)
    }
    err = rows.err()
    if err != nil {
        return err
    }
    return nil
}

错误:

2019/02/26 16:25:55 http: panic serving [::1]:20932: runtime error: invalid memory address or nil pointer dereference
goroutine 11 [running]:
net/http.(*conn).serve.func1(0xc0002badc0)
    c:/go/src/net/http/server.go:1746 +0xd7
panic(0x6dad20, 0x970890)
    c:/go/src/runtime/panic.go:513 +0x1c7
database/sql.(*db).conn(0x0, 0x78a500, 0xc0000100a8, 0x10000c000339801, 0x0, 0xc000339898, 0xc000339830)
    c:/go/src/database/sql/sql.go:1081 +0x41
database/sql.(*db).query(0x0, 0x78a500, 0xc0000100a8, 0xc000356040, 0x3a, 0x0, 0x0, 0x0, 0xc000356001, 0x3a, ...)
    c:/go/src/database/sql/sql.go:1514 +0x6d
database/sql.(*db).querycontext(0x0, 0x78a500, 0xc0000100a8, 0xc000356040, 0x3a, 0x0, 0x0, 0x0, 0x5, 0xc000356040, ...)
    c:/go/src/database/sql/sql.go:1496 +0xda
database/sql.(*db).query(0x0, 0xc000356040, 0x3a, 0x0, 0x0, 0x0, 0x8, 0xc00034e016, 0x1)
    c:/go/src/database/sql/sql.go:1510 +0x89
restify/models.getfactors(0xc000339b28, 0xc00034e016, 0x1, 0xc00034e01e, 0x1, 0x0, 0x0)
    c:/users/nnogerbek/go/src/restify/models/factors.go:18 +0xf6
restify/controllers.glob..func1(0x78a2c0, 0xc00035a000, 0xc000332200)
    c:/users/nnogerbek/go/src/restify/controllers/factors.go:14 +0xd3
net/http.handlerfunc.servehttp(0x74da58, 0x78a2c0, 0xc00035a000, 0xc000332200)
    c:/go/src/net/http/server.go:1964 +0x4b
github.com/gorilla/mux.(*router).servehttp(0xc0002fc180, 0x78a2c0, 0xc00035a000, 0xc000310300)
    c:/users/nnogerbek/go/src/github.com/gorilla/mux/mux.go:212 +0xd7
github.com/gorilla/handlers.(*cors).servehttp(0xc0001f2120, 0x78a2c0, 0xc00035a000, 0xc000310300)
    c:/users/nnogerbek/go/src/github.com/gorilla/handlers/cors.go:54 +0xa95
net/http.serverhandler.servehttp(0xc000056b60, 0x78a2c0, 0xc00035a000, 0xc000310300)
    c:/go/src/net/http/server.go:2741 +0xb2
net/http.(*conn).serve(0xc0002badc0, 0x78a4c0, 0xc000340040)
    c:/go/src/net/http/server.go:1847 +0x64d
created by net/http.(*server).serve
    c:/go/src/net/http/server.go:2851 +0x2fc

数据库/database.go

package database

import (
    "database/sql"
    "fmt"
    "github.com/joho/godotenv"
    _ "github.com/lib/pq"
    "log"
    "restify/utils"
)

var DB *sql.DB

/*
Function: "Connect".

Description:
The main task of the function is to initialize database connection.
*/
func Open() () {
    // Load environment variables from ".env" file.
    err := godotenv.Load(".env")
    if err != nil {
        panic(err)
    }

    // Initialize database related variables.
    dbUser := utils.CheckEnvironmentVariable("PostgreSQL_USER")
    dbPassword := utils.CheckEnvironmentVariable("PostgreSQL_PASSWORD")
    dbHost := utils.CheckEnvironmentVariable("PostgreSQL_HOST")
    dbName := utils.CheckEnvironmentVariable("PostgreSQL_DATABASE_NAME")

    // Defining connection string for PostgreSQL database.
    dbURL := fmt.Sprintf("user=%s password=%s host=%s dbname=%s sslmode=disable", dbUser, dbPassword, dbHost, dbName)

    // Create PostgreSQL database connection pool.
    DB, err := sql.Open("postgres", dbURL)
    if err != nil {
        panic(err)
    }

    // Ping PostgreSQL database to make sure it's alive.
    err = DB.Ping()
    if err != nil {
        panic(err)
    }

    log.Println("REST API web service successfully connected to remote PostgreSQL database.")
}

/*
Function: "Disconnect"

Description:
The main task of the function is to disconnect database connection.
*/
func Close() error {
    return DB.Close()
}

解决方案


问题似乎出在此处分配数据库时:

db, err := sql.open("postgres", dburl)

数据库在新范围中定义,因此这会创建一个局部变量而不是设置 pkg 级别变量。 因此,代码 open() 建立了与数据库的连接。

试试这个:

var err error
DB, err = sql.Open("postgres", dbURL)

以下是官方引用:

与常规变量声明不同,短变量声明可以重新声明变量,前提是它们最初在同一块(或参数列表,如果该块是函数体)中以相同的类型声明,并且至少有一个非-空白变量是新的。因此,重新声明只能出现在多变量短声明中。重新声明不会引入新变量;它只是为原始值分配一个新值。

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