Is_type_of and is_a_category_for vs: belongs_to and has_many

Rails
1

Hello experts,
I wonder if I’m the only one who is running into this conceptual
stumbling block…

Suppose I have a database of documents, and I want to categorize the
documents. I can model this as:

class document_category < ActiveRecord::Base
has_many :documents
end

class document < ActiveRecord::Base
belongs_to :document_category
end

but, semantically, I would rather write:

class document < ActiveRecord::Base
is_type_of :document_category
end

class document_category < ActiveRecord::Base
is_a_category_for :documents
end

(Or use some other sort of verbiage).
The focus of my database is on the the documents, not the categories.
The user entry fields are all going to be document-centric, (with,
probably a drop-down box selecting the category for a document).

This is inverted from the classic Rails tutorials where a post might
have many comments, or a supplier might have many widgets.

I am curious what folks do in this situation… Have you just learned
(as I will) to live with the underlying meaning of “has_many” and
“belongs_to”? Or do you define your own relationship mappings
according to your problem domain. (If so, how would one do that?)

–wpd

2

Patrick D. wrote:

but, semantically, I would rather write:

class document < ActiveRecord::Base
is_type_of :document_category
end

class document_category < ActiveRecord::Base
is_a_category_for :documents
end

At the end of config/environment.rb, if you put:

class << ActiveRecord::Base
alias_method :is_type_of, :belongs_to
alias_method :is_a_category_for, :has_many
end

then you can use these instead.

3

On Mon, Mar 17, 2008 at 3:35 PM, Mark B.
[email protected] wrote:

At the end of config/environment.rb, if you put:

class << ActiveRecord::Base
alias_method :is_type_of, :belongs_to
alias_method :is_a_category_for, :has_many
end

then you can use these instead.
Thanks. That’s a handy trick to know. I’ll use that.

From a coding style perspective, is this what people generally do? Or
does everybody accept and understand the semantic meanings of
belongs_to and has_many?

–wpd

4

Patrick D. wrote:

From a coding style perspective, is this what people generally do? Or
does everybody accept and understand the semantic meanings of
belongs_to and has_many?

Personally, I always just use has_many/belongs_to as that is the
relationship between the models.

If you use something non-standard, then someone else coming to your code
would have to look for the definition in documentation or the source
somewhere, no matter how clear the names, to be certain in themselves
what is meant. That doesn’t mean you shouldn’t do it. Rails is
opinionated, but not restrictive.