Question

I have a problem in C# in how to handle Error in try – catch.

Example I write code for delete record into database but this record has FK into another table. How to handle this?

try
{
     // delete record in database
}
catch (Exception ex)
{
    int error = // how to get this code exception      
}

Answer 1

try
{
    # SQL Stuff
}
catch (SqlException ex)
{
    if (ex.Errors.Count > 0) // Assume the interesting stuff is in the first error
    {
        switch (ex.Errors[0].Number)
        {
            case 547: // Foreign Key violation
                throw new InvalidOperationException("Some helpful description", ex);
                break;
            case 2601: // Primary key violation
                throw new DuplicateRecordException("Some other helpful description", ex);
                break;
            default:
                throw new DataAccessException(ex);
        }
    }

}

as per foreign-key-violation

Take a look at:
how-to-handle-db-exception-in-c-sharp

Which will tell you how to precisely locate the foreign key error.

Also look at MSDN Row Deletion including foreign keys

Which explains about setting cascade to on – which is what I believe you are missing.