Wolfgang Kinkeldei

Today, we watched a series of test cases failing. Our tests started with a blank database and a series of populate method-calls to create their own test records.

Everything looked obviously right, but after a while of debugging, we found out that the populate method of DBIx::Class::ResultSet behaves differently depending on the context used. In Scalar or List context, the records are inserted using the INSERT statement, while in void context, a bulk insert method is used.

From a performance standpoint, this absolutely makes sense. The documentation does explain this very well.

However, some optimizations have been made under the hood that are not obvious unless you know about -- I did not know that before.

My code looked like this:

    MyApp->model('DB::Element')->populate([
        {element_id => 113, name => 'f4'},
        {element_id => 114, name => 'f5', usage_starts => '2000-04-01'},
    ]);

And the statement sent to the database was:

INSERT INTO element( element_id, name ) 
  VALUES( ?, ? ) : '__BULK_INSERT__'

Every column which was not mentioned in the first record got lost and simply was ignored.

Conclusion? A bulk insert can only operate on a well known set of columns. The logic behind DBIx::Class retrieves the set of rows from the keys of the first hashref. This is important to keep in mind when using this syntax.

Solutions? TIMTOWTDI :-) If speed is not important, a populate method call could easily put into list context forcing the usage of single insert statements that do what you expect.

    # force list context, ugly but usable :-)
    () = MyApp->model('DB::Element')->populate([
        # ...
    ]);