Question

Recently I’ve been working on some Perl projects and I’m a very novice Perl programmer. I’ve been experimenting with DBIx::Class and so far I’m really please with the flexibility and the ease of use. I’m curious though. I come from a .NET background and it seems like we spend a lot of time abstracting our DAL to a certain degree. Is this a good idea with a language like Perl?

Where I want to get shortly is to have the ability to start mocking my DAL so I can write unit tests for tasks. Right now though I’m struggling with how the overall structure and design of the application should look though?

Answer 1

Re: Relationship of the ORM within the application…

Hopefully this is the kind of answer you are looking for…

With most web app frameworks in the “scripting” world (i.e. perl, ruby, python, php), most of the time I’ve seen the business logic implemented at the ORM object level. E.g. in a Rails app it’s at the ActiveRecord level; if you are using DBix::Class it would be at the Result-class level.

More concretely, in the case of DBIx::Class, if you have a table named VENDOR there would be a class called MySchema::Result::Vendor which represents a single row in the table VENDOR. Simply add your business methods to this class.

One disadvantage of this approach is that it ties your business logic with the ORM class which can make (unit) testing more difficult. One solution to this is to use a light-weight database for unit tests (i.e. SQLite), and an ORM like DBIx::Class will facilitate switching between the two. Of course, this won’t work if you rely on SQL features which are not implemented in SQLite.

Another approach is to place your business logic methods into a Moose role. Then those methods can be composed into either the DBIx::Class Result class or into a mock object for testing. I can elaborate with an example if you’d like.

One big assumption of the above is that your business object = one row in the database. If this is not the case (i.e. you business object spans more than one table), then you’ll probably want to create a “shell” or container object which has as instance members each of the constituent ORM objects. Fortunately, Moose has a nice facility for delegating methods (search for Moose delegation and the handles attribute of instance member declarations), so it is relatively easy to make a composite business object out of two or more ORM objects. Again, I can give you an example of this if you’d like.

HTH