Question

我正在编写一个从sql数据库中读取数据的函数，其功能如下，

public override Dictionary<string, DbDataReader> GetData()
{
    using (_connection)
    {
        Dictionary<string, DbDataReader> dataDictionary = new Dictionary<string, DbDataReader>();
        _xmlDoc.Load("Queries.xml");
        XPathNavigator navigator = _xmlDoc.CreateNavigator();
        XPathNodeIterator iterator = navigator.Select("//query");
        while (iterator.MoveNext())
        {
            _command = new SqlCommand(iterator.Current.ToString());
            _command.Connection = _connection;
            _command.CommandText = iterator.Current.ToString();
            SqlDataReader reader = _command.ExecuteReader();

            dataDictionary.Add(iterator.Current.GetAttribute("name", ""), reader);
        }
        return dataDictionary;
    }
}

但我得到一个编译器错误，说明：

无法转换来源类型＆＃39; system.data.common.dbdatareader＆＃39;达到目标键入＆＃39; system.data.sqlclient.sqldatareader＆＃39;

但我查看了MSDN：https://msdn.microsoft.com/en-us/library/9kcbe65k(v=vs.110).aspx

它表示ExecuteReader（）的返回类型是＆＃39; system.data.sqlclient.sqldatareader＆＃39;

任何人都可以帮助我吗？谢谢！

Answer 1

您的方法正在寻找Dictionary<string, DbDataReader>的返回类型，但您将返回Dictionary<string, SqlDataReader>。

public override Dictionary<string, DbDataReader> GetData()
{
    using (_connection)
    {
         Dictionary<string, DbDataReader> dataDictionary = new Dictionary<string, DbDataReader>();
         xmlDoc.Load("Queries.xml");
         XPathNavigator navigator = _xmlDoc.CreateNavigator();
         XPathNodeIterator iterator = navigator.Select("//query");
         while (iterator.MoveNext())
         {
             DbCommand _command = db.GetSqlStringCommand(iterator.Current.ToString());
             IDataReader dataReader = db.ExecuteReader(_command);

              dataDictionary.Add(iterator.Current.GetAttribute("name", ""), dataReader);
         }
         return dataDictionary;
   }
}

Answer 2

更新代码将DbDataReader替换为IDataReader ..

public Dictionary<string, IDataReader> GetData()
    {
        using (_connection)
        {
            Dictionary<string, IDataReader> dataDictionary = new Dictionary<string, IDataReader>();
            _xmlDoc.Load("Queries.xml");
            XPathNavigator navigator = _xmlDoc.CreateNavigator();
            XPathNodeIterator iterator = navigator.Select("//query");
            while (iterator.MoveNext())
            {
                _command = new SqlCommand(iterator.Current.ToString());
                _command.Connection = _connection;
                _command.CommandText = iterator.Current.ToString();
                IDataReader reader = _command.ExecuteReader();

                dataDictionary.Add(iterator.Current.GetAttribute("name", ""), reader);
            }
            return dataDictionary;
        }

    }

SqlDataCommand.ExecuteReader（）时返回DbDataReader

2 个答案: