从方法返回的DataReader [英] Return datareader from method

问题描述

我有以下方法

    public static SqlDataReader MenuDataReader(string url)
    {
        using (SqlConnection con = new SqlConnection(connectionString))
        {
            using (SqlCommand cmd = new SqlCommand("spR_GetChildMenus", con))
            {
                cmd.CommandType = CommandType.StoredProcedure;
                cmd.Parameters.AddWithValue("@PageUrl", url);
                cmd.Parameters.AddWithValue("@MenuId", ParameterDirection.Output);
                cmd.Parameters.AddWithValue("@ParentId", ParameterDirection.Output);
                cmd.Parameters.AddWithValue("@TitleText", ParameterDirection.Output);
                cmd.Parameters.AddWithValue("@ExternalUrl", ParameterDirection.Output);
                cmd.Parameters.AddWithValue("@FullUrl", ParameterDirection.Output);
                cmd.Parameters.AddWithValue("@ChildCount", ParameterDirection.Output);
                con.Open();
                SqlDataReader reader = cmd.ExecuteReader();
                if (reader.HasRows)
                {
                    //return reader;

                    while (reader.Read())
                    {
                        return reader;
                    }

                }
            }
        }
        return null;
    }

这IM调用像这样

which im calling like this

        SqlDataReader reader = MenuDataReader(url);
        if (reader.HasRows)
        {
            while (reader.Read())
            { }}

然而即时得到错误信息

however im getting the error message

无效试图调用HasRows当读者是封闭的。

Invalid attempt to call HasRows when reader is closed.

谁能帮我出

感谢

推荐答案

你真的需要的读者，还是你只是需要一些方法来遍历里面的行？我建议一个的迭代器块的。您可以将行遍历源法里面，收益各行依次调用者。

Do you really need the reader, or do you just need some way to iterate over the rows inside it? I suggest an iterator block. You can iterate over your rows inside the source method, and yield each row in turn to the caller.

有与此技术一拧：因为你的收益的相同的每次迭代，有些情况下这可能会导致一个问题，所以你最好也要求对象委托某处复制行的内容。我也喜欢到可以用于任何的查询，并使用相同的代表技术来处理参数的数据，像这样的抽象给通用方法：

There is a twist with this technique: because you're yielding the same object with each iteration, there are cases where this can cause a problem, and so you're best off also asking for a delegate to copy the contents of the row somewhere. I also like to abstract this to a generic method that can be used for any query, and use the same delegate technique to handle parameter data, like so:

private IEnumerable<T> GetRows(string sql, Action<SqlParameterCollection> addParameters, Func<IDataRecord, T> copyRow)
{
     using (var cn = new SqlConnection("Connection string here"))
     using (var cmd = new SqlCommand(sql, cn)
     {
         cmd.CommandType = CommandType.StoredProcedure;
         addParameters(cmd.Parameters);
         cn.Open();
         using (var rdr = cmd.ExecuteReader())
         {
             while (rdr.Read())
             {
                 yield return copyRow(rdr);
             }
             rdr.Close();
         }
     }
}

public IEnumerable<MenuItem> GetChildMenus(string url)
{
     return GetRows("spR_GetChildMenus", p =>
     {
         //these lines are copied from your question, but they're almost certainly wrong
         p.AddWithValue("@PageUrl", url);
         p.AddWithValue("@MenuId", ParameterDirection.Output);
         p.AddWithValue("@ParentId", ParameterDirection.Output);
         p.AddWithValue("@TitleText", ParameterDirection.Output);
         p.AddWithValue("@ExternalUrl", ParameterDirection.Output);
         p.AddWithValue("@FullUrl", ParameterDirection.Output);
         p.AddWithValue("@ChildCount", ParameterDirection.Output);
     }, r =>
     {
         return new MenuItem( ... );
     }
 }

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