Go測驗失敗db查詢（零指標）但適用于Postman/Curl

我正在測驗 GetCats()，它是一個從 mysql 資料庫中獲取所有“貓”的函式。當我通過郵遞員到達端點時，由于“COALESCE”將欄位設定為空字串（如果為空），因此不會出現空指標錯誤。

但是，當我測驗該函式時，出現了一個 nil 指標錯誤并且程式崩潰了。

• panic: runtime error: invalid memory address or nil pointer dereference [recovered]

_test.go

func TestGetCats(t *testing.T) {
    // create new request to /cats endpoint, nil => body io.Reader
    req, err := http.NewRequest("GET", "/cats", nil)
    if err != nil {
        t.Fatal(err)
    }
    // Will store response received from /cats endpoint => pointer to ResonseRecorder struct
    recorder := httptest.NewRecorder()

    handler := http.HandlerFunc(handlers.GetCats)

    // ----(FAILS HERE) hit endpoint with recorder and request (FAILS HERE) ----//
    handler.ServeHTTP(recorder, req)

    // ------------------------------------------------------------------------//

    // test recorder status code
    if recorder.Code != http.StatusOK {
        t.Errorf("getCats return wrong status code: got %v but want %v", recorder.Code, http.StatusOK)
    }

cathandlers.go

func GetCats(w http.ResponseWriter, r *http.Request) {
    w.Header().Set("Content-Type", "application/json")

    var animals []Animal

    // ---------------Program panics on this query --------------------//
    // cannot input null values into struct => return empty string instead
    
    res, err := Db.Query("SELECT id, name, 
                            COALESCE(age, '') as age, 
                            COALESCE(color, '') as color,
                            COALESCE(gender, '') as gender, 
                            COALESCE(breed, '') as breed, 
                            COALESCE(weight, '') as weight FROM cats")

    //------------------------------------------------//

任何幫助將不勝感激！

額外說明：

• 'name' 在資料庫中不為空，不需要在該欄位上合并
• 資料庫中有幾個空欄位（故意的）
• 只是對查詢在郵遞員中的作業方式感到困惑，但在從 _test.go 內部呼叫時卻沒有

uj5u.com熱心網友回復：

可能 Db 物件在測驗中沒有正確初始化。您最好定義一個結構并將 DB 作為依賴項注入，并在測驗中使用假 DB 物件。例如，

// handlers.go
import (
        "database/sql"
        "net/http"
)

type App struct {
        DB *sql.DB
}

func (a *App) GetCats(w http.ResponseWriter, r *http.Request) {
        // var animals []Animal

        res, err := a.DB.Query("SELECT id, name, 
                            COALESCE(age, '') as age, 
                            COALESCE(color, '') as color,
                            COALESCE(gender, '') as gender, 
                            COALESCE(breed, '') as breed, 
                            COALESCE(weight, '') as weight FROM cats")

      // ....
}

// handlers_test.go
import (
        "net/http"
        "net/http/httptest"
        "testing"

        "github.com/DATA-DOG/go-sqlmock"
)

func TestGetCats(t *testing.T) {
        db, _, err := sqlmock.New()
        if err != nil {
                t.Fatalf("an error %s was not expected when openning a stub database connection", err)
        }

        app := &App{
                DB: db,
        }

        req, err := http.NewRequest("GET", "/cats", nil)
        if err != nil {
                t.Fatal(err)
        }
        // Will store response received from /cats endpoint => pointer to ResonseRecorder struct
        recorder := httptest.NewRecorder()

        // DB expected actions...

        handler := http.HandlerFunc(app.GetCats)
        handler.ServeHTTP(recorder, req)

        if recorder.Code != http.StatusOK {
                t.Errorf("getCats return wrong status code: got %v but want %v", recorder.Code, http.StatusOK)
        }
}

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