Question

我是开始的新手，需要帮助！

在PostgreSQL数据库中，我有一个名为factors的表。该表具有2列（factor_id和factor_name）。现在，我已经从Go应用程序成功连接到PostgreSQL数据库。

当我尝试在控制台中进行基于查询的GET请求时，我看到错误。

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

我在哪里犯错？请帮助我解决问题。

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

database / 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()
}

Answer 1

问题似乎在于何时在此处分配数据库：

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

将在新的作用域中定义数据库，因此将创建局部变量，而不是设置pkg级别变量。因此，代码Open()建立了与DB的连接。

尝试一下：

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

这是官方报价：

与常规变量声明不同，简短的变量声明可以重新声明变量，前提是它们最初是在相同类型的同一块中（如果该块是函数体，则在参数列表中）早先声明过，且具有相同的类型，并且至少是一个-空白变量是新的。因此，重新声明只能出现在多变量简短声明中。重新声明不会引入新变量；只是为原始值分配了一个新值。

运行时错误：无效的内存地址或nil指针取消引用（2）

1 个答案: