c# - How can I catch UniqueKey Violation exceptions with EF6 and SQL Server?

Question

One of my tables have a unique key and when I try to insert a duplicate record it throws an exception as expected. But I need to distinguish unique key exceptions from others, so that I can customize the error message for unique key constraint violations.

All the solutions I've found online suggests to cast ex.InnerException to System.Data.SqlClient.SqlException and check the if Number property is equal to 2601 or 2627 as follows:

try
{
    _context.SaveChanges();
}
catch (Exception ex)
{
    var sqlException = ex.InnerException as System.Data.SqlClient.SqlException;

    if (sqlException.Number == 2601 || sqlException.Number == 2627)
    {
        ErrorMessage = "Cannot insert duplicate values.";
    }
    else
    {
        ErrorMessage = "Error while saving data.";
    }
}

But the problem is, casting ex.InnerException to System.Data.SqlClient.SqlException causes invalid cast error since ex.InnerException is actually type of System.Data.Entity.Core.UpdateException, not System.Data.SqlClient.SqlException.

What is the problem with the code above? How can I catch Unique Key Constraint violations?

Answer 1

With EF6 and the DbContext API (for SQL Server), I'm currently using this piece of code:

try
{
  // Some DB access
}
catch (Exception ex)
{
  HandleException(ex);
}

public virtual void HandleException(Exception exception)
{
  if (exception is DbUpdateConcurrencyException concurrencyEx)
  {
    // A custom exception of yours for concurrency issues
    throw new ConcurrencyException();
  }
  else if (exception is DbUpdateException dbUpdateEx)
  {
    if (dbUpdateEx.InnerException != null
            && dbUpdateEx.InnerException.InnerException != null)
    {
      if (dbUpdateEx.InnerException.InnerException is SqlException sqlException)
      {
        switch (sqlException.Number)
        {
          case 2627:  // Unique constraint error
          case 547:   // Constraint check violation
          case 2601:  // Duplicated key row error
                      // Constraint violation exception
            // A custom exception of yours for concurrency issues
            throw new ConcurrencyException();
          default:
            // A custom exception of yours for other DB issues
            throw new DatabaseAccessException(
              dbUpdateEx.Message, dbUpdateEx.InnerException);
        }
      }

      throw new DatabaseAccessException(dbUpdateEx.Message, dbUpdateEx.InnerException);
    }
  }

  // If we're here then no exception has been thrown
  // So add another piece of code below for other exceptions not yet handled...
}

As you mentioned UpdateException, I'm assuming you're using the ObjectContext API, but it should be similar.