Nested resource with multiple parent resources in Rails 3

I want to create a model to store comments related to articles. I have a strong feeling that in the future开发者_如何学运维 I will want comments on other objects in the app too. How do I design commenting in my app so that it will be forward compatible with adding new parent objects. I want to avoid a scenario where have multiple controllers/models for each object to comment relationship.

After watching Ryan Bates screen cast on Nested Resource I have a firm grasp on how tp nest a resource under a single parent. How do I achieve this under 2 or more parent resources?

Thanks!

For "forward compatible with adding new parent objects" part of the question:

You could use Polymorphic Associations. Here's a nice example. Also see RailsCast #154.

An example of how it could look like for you:

The comments table columns' could be like this:

id:integer
commentable_type:string
commentable_id:integer
comment_text:string

Some Sample records:

1,'Article',12,'My first comment' #comment on an Article model
2,'Question',12,'My first comment' #comment on a Question model
3,'Question',15,'My first comment' #comment on a Question model

To answer the part about the routes and finding the resource.

The usual rails controller would find the child resource from the parent.

GET /articles/{parent_id}/comments/{id}

GET /articles/0/comments/1

article = articles.find(parent_id = 0)
comment = article.comments.find(id = 1)

You can't do that with polymorphic parents. You would have to find the parent from the child.

GET /article/{parent_id}/comments/{id}
GET /questions/{parent_id}/comments/{id}

GET /article/0/comments/1
GET /questions/0/comments/1

parent = comments.select(parent_id = 0).parent
comment = parent.comments.find(id = 1)

It might possible to make your routes pass a type to the controller.

GET /{parent_type}/{parent_id}/comments/{id}

GET /article/0/comments/1
GET /questions/0/comments/1

parent = parent_type.find(parent_id = 0)
comment = parent.comments.find(id = 1)

(I've not tried this approach, this is obviously pseudocode.)

Edit ...

I suppose you could also just add one parameters for each type of parent.

GET /article/{article_id}/comments/{id}
GET /questions/{question_id}/comments/{id}

GET /article/0/comments/1
GET /questions/0/comments/1

if article_id
    article = articles.find(article_id = 0)
    comment = article.comments.find(id = 1)

if question_id
    question = questions.find(question_id = 0)
    comment = question.comments.find(id = 1)