Question

我遇到了SQL阅读器类的问题。

我在数据库上有一个名为Airport的自定义对象。但是我无法正确使用datareader。当我尝试将所有机场提取到一个列表中时（参见下面的方法2），在将对象添加到列表之前，似乎跳转了while（_reader.Read（））循环。

有什么建议吗？

要提取对象，我使用3种方法：

要查找特定对象：

public Airport FindAirportByCode(string _airportCode)
{
    con.Open();
    string query = "SELECT * from Airport WHERE airportCode = '" + _airportCode + "'";
    SqlCommand cmd = new SqlCommand(query, con);
    SqlDataReader _reader = cmd.ExecuteReader();

    Airport retAirport = BuildAirport(_reader);
    _reader.Close();
    con.Close();
    return retAirport;
}

将所有机场列入名单

public List<Airport> SelectAll()
{
    con.Open();
    List<Airport> airports = new List<Airport>();
    string query = "SELECT * from Airport";
    SqlCommand cmd = new SqlCommand(query, con);

    SqlDataReader _reader = cmd.ExecuteReader();

    while (_reader.Read())
    {
        Airport temAirport = new Airport();
        temAirport = BuildAirport(_reader);
        airports.Add(temAirport); // It seems to skip this step and only add the last Airport from BuildAirport to the list.
    }

    _reader.Close();
    con.Close();
    return airports;
}

将其构建为C＃

中的对象

    private Airport BuildAirport(SqlDataReader _reader)
{

    Airport temAirport = new Airport();
    while (_reader.Read())
    {
        temAirport.airportCode = (string) _reader["airportCode"];
        temAirport.airportName = (string) _reader["airportName"];
        temAirport.country = (string) _reader["country"];
        temAirport.city = (string) _reader["city"];
    }
    _reader.Close();



    return temAirport;
}

Answer 1

在第三步中，您再次冒充reader，这就是为什么当您想要检索所有机场时，您只能获得一个机场。

private Airport BuildAirport(SqlDataReader _reader)
{

    Airport temAirport = new Airport();
    temAirport.airportCode = (string) _reader["airportCode"];
    temAirport.airportName = (string) _reader["airportName"];
    temAirport.country = (string) _reader["country"];
    temAirport.city = (string) _reader["city"];
    return temAirport;
}

现在我们必须更改您的第一种方法，因为更改BuildAirport会破坏它。我们现在必须在FindAirportByCode中阅读一行。

public Airport FindAirportByCode(string _airportCode)
{
    con.Open();
    string query = "SELECT * from Airport WHERE airportCode = @airportCode";
    SqlCommand cmd = new SqlCommand(query, con);
    cmd.Parameters.AddWithValue("@airportCode", _airportCode);

    SqlDataReader _reader = cmd.ExecuteReader();

    Airport retAirport = null;
    if (_reader.Read())
    {
         retAirport = BuildAirport(_reader);
    }

    _reader.Close();
    con.Close();
    return retAirport;
}

使用参数化查询来保证安全。

使用SQL datareader在c＃中提取1到多个自定义对象

1 个答案: