Creating a comments system for multiple types of content

Hi all

My site has news entries, it has a party calendar and it has a blog.
Now I’d like to create a commenting system that in fact is quite simple,
but I wanna use it for all these 3 types of content.
My question: how can I do that? I maybe could add an association to all
three types in the comment model:

class Comment < ActiveRecord::Base
belongs_to :news_item
belongs_to :party
belongs_to :blog_entry

And in all the three models I then added a “has_many :comments”
statement. This would work, but every comment entry would belong only to
one of the three models, so there were many NULL values that seem
incorrect to me.
And when another content type would be created (like party_report) I
would have to update the comment model and it would get more and more
xxx_id fields and NULL values.

Do you see a better way for doing this? I’m still looking for a “clean”
way, but I can’t really find one using the Rails stuff I know.

My idea is something like having another attribute in the comment model
that specifies the sort of content (model) it is associated with:

create_table :comments do |t|
t.column “subject”, :string, :null => false
t.column “body”, :text, :null => false
t.column “model_type_id”, :integer, :null => false
t.column “model_type”, :varchar, :null => false

Then the data rows could look like these:

This item is associated with news_item ID = 1

subject: “this is a comment”
body: “and this is its content”
model_type_id: 1
model_type: “news_item”

This item is associated with news_item ID = 2

subject: “this is another comment”
body: “and this is another content”
model_type_id: 2
model_type: “news_item”

This item is associated with party ID = 5

subject: “this is yet another comment”
body: “and this is yet another content”
model_type_id: 5
model_type: “party”

This item is associated with blog ID = 99

subject: “this is a blog comment”
body: “and this is a blog comment content”
model_type_id: 99
model_type: “blog_entry”

Do you see what I mean? Wouldn’t this be beautiful? If I wanted to add
the party_report to it I only had to add the statement “belongs_to
:party_report” to the comment model and “has_many :comments” to the
party_report model and then I could begin adding comments without having
to change anything in the database table!

This item is associated with party_report ID = 421

subject: “yeah great party”
body: “blah blah blah”
model_type_id: 421
model_type: “party_report”

Is there some way to achieve this? This would be REALLY GREAT! And Rails
is called “great”, so I’m looking forward! :wink:


that is what i use for my website
i also use (for example)

class People < ActiveRecord::Base
has_many :comments, :conditions => [‘kind = ?’, ‘people’], :include =>
:user, :order => ‘created_at DESC’

…other stuff…


the :include => :user stuff gets the user who wrote the comment
i write the same stuff for other kinds of models

it feels a bit clumsy for me, because the thing is you can’t go the
way. for a comment, i would like to get the item commented like for
comment.commented_item but i haven’t found a way.

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