how to check if a datareader is null or empty - Error

Question

I am using Sqlite as a back End and Windows Form Application (C#) as a front end.

I am going through this code:

cmdgetTransaction_ID = new SQLiteCommand("SELECT MAX(transaction_id) as expr1  FROM  transaction_master WHERE transaction_id LIKE '"+temp+"%' ", con);
SQLiteDataReader reader = cmdgetTransaction_ID.ExecuteReader();
if (reader["expr1"]!=DBNull.Value)
{
     name= reader.GetString(0);
     string[] substrings = System.Text.RegularExpressions.Regex.Split(name, "([a-z]+)|([0-9]+)");
     MessageBox.Show(substrings[0]);
}
else
{
     name=name+temp+"1";
     lblTranID.Text = name;
}

I have also tried with this: if (reader.IsDBNull(0))

While debugging (step into) it reports following Exception :

A first chance exception of type 'System.InvalidOperationException' occurred in System.Data.SQLite.dll

I can not figure it out what mistake i am doing, so that it generates an exception.

Either you title is misleading or content. Do you want check if reader has rows or null for individuals columns? — Nikhil Vartak, Nov 04 '15 at 02:52
Check this http://stackoverflow.com/questions/4393092/c-sharp-a-first-chance-exception-of-type-system-invalidoperationexception — Gagan Jaura, Nov 04 '15 at 03:04
@dotnetkid - Actually i am interested in , to check whether my datareader object is null or does it have any record at all — user2130649, Nov 04 '15 at 03:06
Then just do `if (reader != null) { while (reader.Read()) { .. } }` — Nikhil Vartak, Nov 04 '15 at 03:10
I have learnt and implemented this from http://stackoverflow.com/questions/3432974/datareader-is-null-or-empty — user2130649, Nov 04 '15 at 03:10
@dotnetkid :- Even though ,data reader does not contain any record the if condition becomes true ,it goes into while loop, as there is no data it raises an exception — user2130649, Nov 04 '15 at 03:30
@dotnetkid: Still the problem persist ! - I Have attached screen shots as well — user2130649, Nov 04 '15 at 04:24

score 1 · Answer 1 · answered Nov 04 '15 at 03:37

1

This should work for you:

if (reader != null && reader.HasRows) 
{
   while (reader.Read()) 
   {
      ...
   }
}

answered Nov 04 '15 at 03:37

Nikhil Vartak

5,002
3
26
32

still the problem persist : Even though ,data reader does not contain any record the if condition becomes true ,it goes into while loop, as there is no data it raises an exception - I have attached Screen Shots – user2130649 Nov 04 '15 at 04:22
Does it raise exception when at `while` line or after that when you try to read `expr1` column? Also do not edit answers for posting own screen shots. Use comments instead. – Nikhil Vartak Nov 04 '15 at 05:23

how to check if a datareader is null or empty - Error

1 Answers1