c# - What's the best way to detect if an IDataReader is empty?

Question

It seems like IDataReader.Read() is always true at least one time (If I'm wrong about this let me know.) So how do you tell if it has no records without just wrapping it in a try/catch?

Answer 1

if(dr.Read())
{
   //do stuff
}
else
{
 //it's empty
}

usually you'll do this though:

while(dr.Read())
{
}

Answer 2

Yes, if you want to use the interface then Read until false is the only way to test. If you are looking for a generic IDataReader implementation, you could try DbDataReader and use the HasRows property.

Answer 3

你可以System.Data.IDataReader投到System.Data.Common.DbDataReader

using (System.Data.IDataReader IReader = ICommand.ExecuteReader())
{
    if (((System.Data.Common.DbDataReader)IReader).HasRows)
    {
        //do stuff
    }
} // End Using IReader 

这是纯粹的邪恶，但它（通常）有效；）

（假设您的实例IDataReader是由自定义 ADO.NET 提供程序实现的，而不是您的某些自定义愚蠢类，它只是实现IDataReader而不是从DbDataReader[which implements IDataReader] 派生）。

Answer 4

刚刚偶然发现这个问题并想出了这个......

bool isBeforeEoF;

do
{
    isBeforeEoF = reader.Read();

    if (isBeforeEoF)
    {
        yield return new Foo()
        {
            StreamID = (Guid)reader["ID"],
            FileType = (string)reader["Type"],
            Name = (string)reader["Name"],
            RelativePath = (string)reader["RelativePath"]
        };         
    }

} while (isBeforeEoF);