無法連接到psql資料庫

我正在嘗試連接到資料庫，但是當我使用該GET方法向端點發出 curl 請求時出現錯誤。我仔細檢查了用戶憑據并授予了完全權限和超級用戶權限。以下是卷曲端點時出現的錯誤：

santosh@pkg*$:curl -i localhost:8080/books/show
HTTP/1.1 303 See Other
Content-Type: text/html; charset=utf-8
Location: /books
Date: Sat, 19 Nov 2022 12:09:52 GMT
Content-Length: 33

<a href="/books">See Other</a>.

與資料庫建立連接，當向資料庫發出請求時會觸發這些錯誤：

santosh@pkg*$:go run main.go 
Database connection successful.
2022/11/19 17:39:47 http: panic serving 127.0.0.1:44324: runtime error: invalid memory address or nil pointer dereference
goroutine 35 [running]:
net/http.(*conn).serve.func1()
        /usr/local/go/src/net/http/server.go:1850  0xbf
panic({0x6960e0, 0x8e5630})
        /usr/local/go/src/runtime/panic.go:890  0x262
database/sql.(*DB).conn(0x0, {0x7593d0, 0xc00011a000}, 0x1)
        /usr/local/go/src/database/sql/sql.go:1288  0x53
database/sql.(*DB).query(0x6?, {0x7593d0, 0xc00011a000}, {0x6da967, 0x13}, {0x0, 0x0, 0x0}, 0x68?)

主要程式：

var db *sql.DB

type Books struct {
    Isbn   string
    Title  string
    Author string
    Price  float32
}

func init() {
    var err error
    args := fmt.Sprintf("host=%s port=%d dbname=%s user='%s' password=%s sslmode=%s", "localhost", 5432, "bookstore", "santosh", "dts123", "disable")
    db, err := sql.Open("postgres", args)
    if err != nil {
        fmt.Printf("Creating Database %s", err)
    }
    if err = db.Ping(); err != nil {
        panic(err)
    }
    fmt.Println("Database connection succussful.")

}

func main() {
    http.HandleFunc("/", index)
    http.HandleFunc("/books", booksIndex)
    http.ListenAndServe(":8080", nil)
}

func index(w http.ResponseWriter, r *http.Request) {
    http.Redirect(w, r, "/books", http.StatusSeeOther)
}

func booksIndex(w http.ResponseWriter, r *http.Request) {
    if r.Method != "GET" {
        http.Error(w, http.StatusText(405), http.StatusMethodNotAllowed)
        return
    }

    rows, err := db.Query("SELECT * FROM books")
    if err != nil {
        http.Error(w, http.StatusText(500), 500)
        return
    }
    defer rows.Close()

    bks := make([]Books, 0)
    for rows.Next() {
        bk := Books{}
        err := rows.Scan(&bk.Isbn, &bk.Title, &bk.Author, &bk.Price)
        if err != nil {
            http.Error(w, http.StatusText(500), 500)
            return
        }
        bks = append(bks, bk)
    }
    if err = rows.Err(); err != nil {
        http.Error(w, http.StatusText(500), 500)
        return
    }

}

我嘗試仔細檢查用戶權限和資料庫格式以及順序。一切都符合代碼。連接已建立，但在查詢資料庫時因緊急情況而失敗。

uj5u.com熱心網友回復：

您沒有正確初始化包級db變數。

:=稱為“短變數宣告”的運算子在其塊范圍內宣告并初始化一個新變數。在外部作用域中具有相同名稱的任何變數都將被“隱藏”。

要正確初始化包級變數，您可以使用普通賦值：

var db *sql.DB

func init() {
    args := fmt.Sprintf("host=%s port=%d dbname=%s user='%s' password=%s sslmode=%s", "localhost", 5432, "bookstore", "santosh", "dts123", "disable")

    var err error
    db, err = sql.Open("postgres", args)
    if err != nil {
        fmt.Printf("Creating Database %s", err)
    }
    // ...
}

或者您可以使用:=但隨后使用不同的變數名稱并確保將其用于分配：

var db *sql.DB

func init() {
    args := fmt.Sprintf("host=%s port=%d dbname=%s user='%s' password=%s sslmode=%s", "localhost", 5432, "bookstore", "santosh", "dts123", "disable")

    _db, err := sql.Open("postgres", args)
    if err != nil {
        fmt.Printf("Creating Database %s", err)
    }
    // ...

    db = _db // set "global"
}

標籤：postgresql去

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