DBNull problem

luozx2504

database:
CREATE procedure UserIsExict
@Uid binary (30),
@UserName binary (30) output
as
select @ UserName = UserName from AlbumLogin where Uid = @ Uid
GO
program:
SqlCommand cmd = new SqlCommand ("UserIsExict", conn);
        cmd.CommandType = CommandType.StoredProcedure;

        cmd.Parameters.Add (new SqlParameter ("@ Uid", SqlDbType.Binary, 30));
        cmd.Parameters ["@ Uid"]. Value = Encoding.UTF32.GetBytes (paraUid);

        cmd.Parameters.Add (new SqlParameter ("@ UserName", SqlDbType.Binary, 30));
        cmd.Parameters ["@ UserName"]. Direction = ParameterDirection.Output;

        conn.Open ();
        cmd.ExecuteNonQuery ();
        conn.Close ();

      return Encoding.UTF32.GetString (((byte []) cmd.Parameters ["@ UserName"]. Value));

error:
Cannot cast an object of type "System.DBNull" to type "System.Byte []"

ymooner

if (cmd.Parameters ["@ UserName"]! = DBNull.Value)
{
 return Encoding.UTF32.GetString (((byte []) cmd.Parameters ["@ UserName"]. Value));

}
else
{
return String.Empty;
}

ymooner

Your return value is null, so no conversion operation is possible

苹果小刀

Judge the return value to deal with it!

richwolfbobo

Treat the reverse value

qwer000

if (Convert.IsDbNull (...))
{
}

bellonxcc

Judge whether it is dbnull or not.

wudi1982

error:
Unable to cast object of type "System.DBNull" to type "System.Byte []"
-------------------------
Young people now! I don't know if I analyze them carefully.

luozx2504

No, I mean why is it returning DBNull, the value of my database is not empty?

luozx2504

I did n’t answer the question, sorry