How to catch SqlException caused by deadlock?

The Microsft SQL Server-specific error code for a deadlock is 1205 so you’d need to handle the SqlException and check for that. So, e.g. if for all other types of SqlException you want the bubble the exception up:

catch (SqlException ex)
{
    if (ex.Number == 1205)
    {
        // Deadlock 
    }
    else
        throw;
}

Or, using exception filtering available in C# 6

catch (SqlException ex) when (ex.Number == 1205)
{
    // Deadlock 
}

A handy thing to do to find the actual SQL error code for a given message, is to look in sys.messages in SQL Server.

e.g.

SELECT * FROM sys.messages WHERE text LIKE '%deadlock%' AND language_id=1033

An alternative way to handle deadlocks (from SQL Server 2005 and above), is to do it within a stored procedure using the TRY…CATCH support:

BEGIN TRY
    -- some sql statements
END TRY
BEGIN CATCH
    IF (ERROR_NUMBER() = 1205)
        -- is a deadlock
    ELSE
        -- is not a deadlock
END CATCH

There’s a full example here in MSDN of how to implement deadlock retry logic purely within SQL.