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The number of models in your Ruby on Rails application is growing and one day you will get a brilliant idea.. Let’s put them to modules (that is to different subdirectories in the modules directory). Well, I had this day some weeks ago and, honestly, it is not a good idea… Helpers and tools in RoR, that work without any problems and manual changes when models do not use modules, will require some manual changes to work.

Here is a list of my experiences…

Paginate Helper

A model name for the paginate helper cannot be :model anymore, you have to write 'module/model'.

For a model without a module:

@book_pages, @books = paginate :book, :per_page => 10

For a model in a module:

@book_pages, @books = paginate 'library/book', :per_page => 10

View

Any reference to a model has to contain also a module name: Model.content_columns has to be written as Module::Model.content_columns.

For a model without a module:

<% for column in Book.content_columns %>
<%=h book.send(column.name) %>

<% end %>

For a model in a module:

<% for column in Library::Book.content_columns %>
<%=h book.send(column.name) %>

<% end %>

Scaffold

Files generated for a model in a module with the scaffold script do not work. It is necessary to fix the two above mentioned problems, that is to fix:

• the paginate problem in a controller
• the view problem in the list.rhtml file

I also tried the AJAXScaffold, but it relies that the model name does not contain also a module name. I tried to fix it, but I did not have a lucky day.

Generate

To create a model in a module with the generate script use the module/model notation, e.g.:

For a model without a module:

ruby script/generate model book

For a model in a module:

ruby script/generate model library/book

Model Relationship

If there is a relationship between models in two different modules, it is necessary to specify the :class_name option, otherwise the model in a different module will not be recognised.

For models not in a module:

class Review < ActiveRecord::Base
  belongs_to    :book
end

For models in different modules:

class Review < ActiveRecord::Base
  belongs_to    :book,
                :class_name => "Library::Book"
end

That is all. To have a model in a module is solvable, but definitely not easy to use.
If you have a lot of models and you decided to store them in different modules, my comments may help you.