有趣的问题我遇到了很有意义。我有一个像这样的通用方法:
public TResult Run<TResult>(Func<SqlDataReader, TResult> resultDelegate)
{
TResult result;
using (SqlDataReader reader = command.ExecuteReader()) // command is SqlCommand with attached SqlConnection
{
result = resultsDelegate(reader);
}
// Some other unrelated code (but that's why result has a variable)
return result;
}
在一种情况下,resultDelegate
的返回类型(TResult
)为IEnumerable<object>
。问题是Run
函数由于延迟执行而立即返回,处理SqlDataReader。稍后在代码中,当我尝试阅读结果时(代理人reader.Read()
,我得到InvalidOperationException: Invalid attempt to call Read when reader is closed.
我很难找到解决这个问题的最佳方法。我知道我可以返回一个具体的清单,但如果可能的话我想避免这样做。我也可以在委托中移动using语句,但是再一次,如果我可以避免为每个委托做这个,那就太好了。有什么想法吗?
答案 0 :(得分:5)
也许:
public TResult Run<TResult>(Func<SqlDataReader, TResult> resultDelegate)
{
TResult result;
using (SqlDataReader reader = command.ExecuteReader()) // command is SqlCommand with attached SqlConnection
{
result = resultsDelegate(reader);
if (typeof(TResult) == typeof(IEnumerable<object>))
{
var enumerable = result as IEnumerable<object>;
if (enumerable != null)
{
result = enumerable.ToList();
}
}
}
// Some other unrelated code (but that's why result has a variable)
return result;
}