轉：在json響應中從數據庫複製各種類型的數據

Question

我試圖從我的數據庫中獲取一組數據並將它們以json格式返回。然而，他們是不同的類型，我似乎在我的代碼中使用了錯誤的返回類型。

轉到：

type Script struct { 
    Id   int `json:"id"` 
    Type  string `json:"type"` 
    Created_at int `json:"created_at"` 
} 

type AllContent struct { 
    New_content  []*Script `json:"new_content,omitempty"` 
} 

func ReadAllContent() [][]interface{} { 
    err := db.Ping() 
    if err != nil { 
     log.Fatal(err) 
} 
    rows, err := db.Query("SELECT id, type, created_at FROM script WHERE user_id = $1", user_id) 
    if err != nil { 
     log.Fatal(err) 
    } 
    defer rows.Close() 
    var Type string 
    var created_at, id int 
    for rows.Next() { 
     err := rows.Scan(&id, &Type, &created_at) 
     if err != nil { 
      log.Fatal(err)  
     } 
     var a []interface{} 
     var b []interface{} 
     a = append(a, id, Type, created_at) 
     b = append(b, a) 
    } 
    return b 
} 

func pingHandler(w http.ResponseWriter, r *http.Request) { 

    var s []Script 
    resp := AllContent{New_content: []*Script{}} 
    m := ReadAllContent() 

    for i := 0; i < len(m); i++ { 
     s = append(s, Script{Id: m[i][0], Type: m[i][1], Created_at: m[i][2]) 
    } 
    for i := 0; i < len(m); i++ { 
     resp.New_content = append(resp.New_content, &s[i]) 
    } 

    w.Header().Set("Content-Type", "application/json") 

    js, _ := json.Marshal(resp) 
    w.Write(js) 
} 

我得到這個錯誤：

cannot use m[i][0] (type interface {}) as type int in field value: need type assertion 

我應該怎麼解決？

Answer 1

您可以通過添加類型斷言修復編譯器錯誤：

s = append(s, Script{Id: m[i][0].(int), Type: m[i][1].(string), Created_at: m[i][2].(int)) 

一個更好，更簡單的方法是返回腳本的切片從ReadAllContent對象：

func ReadAllContent() []*Script { 
    var result []*Script 
    err := db.Ping() 
    if err != nil { 
     log.Fatal(err) 
    } 

    rows, err := db.Query("SELECT id, type, created_at FROM script WHERE user_id = $1", user_id) 
    if err != nil { 
     log.Fatal(err) 
    } 
    defer rows.Close() 
    for rows.Next() { 
     s := &Script{} 
     err := rows.Scan(&s.ID, &s.Type, &s.Created_at) 
     if err != nil { 
      log.Fatal(err)  
     } 
     result = append(result, s) 
    } 
    return result 
} 

然後，您可以編碼從ReadAllContent直接返回到JSON：

func pingHandler(w http.ResponseWriter, r *http.Request) { 
    w.Header().Set("Content-Type", "application/json") 
    if err := json.NewEncoder(w).Encode(&AllContent{New_content: ReadAllContent()}); err != nil { 
     // handle error 
    } 
}