# RESTful habtm

**URL:** <https://www.ruby-forum.com/t/restful-habtm/134660>\
**Category:** Rails\
**Created:** [April 13, 2008, 4:37pm UTC](https://www.ruby-forum.com/t/restful-habtm/134660 "2008-04-13T16:37:19Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![pie-r-squared](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/c77e96/32.png) [@pie-r-squared](https://www.ruby-forum.com/u/pie-r-squared)\
**Post date:** [April 13, 2008, 4:37pm UTC](https://www.ruby-forum.com/t/restful-habtm/134660/1 "2008-04-13T16:37:19Z")

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(Note: using Rails 2.0.2)

I have users and groups, with a habtm association, and I want to provide  
a  
RESTful interface to adding and removing those associations. This is  
independent from creating and deleting users or groups. It also isn’t  
quite  
as simple as treating the associations as resources, because I want to  
be  
able to provide an interface to all of the following:

- add a user to a group
- remove a user from a group
- add a group to a user
- remove a group from a user
- set the list of users in a group
- set the list of groups a user is in

I believe this is a use case for nested resources, but I’m not clear on  
how  
to go about it either in terms of routing or in the controller.  
Would someone explain how to go about it?

–Greg

---

<div class="post-metadata">

**Author:** ![pie-r-squared](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/c77e96/32.png) [@pie-r-squared](https://www.ruby-forum.com/u/pie-r-squared)\
**Post date:** [April 14, 2008, 6:18pm UTC](https://www.ruby-forum.com/t/restful-habtm/134660/2 "2008-04-14T18:18:40Z")

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The purpose of nesting resources is to say ‘it only makes sense to  
retrieve this object through this other object’. A simple example is  
for a Blog – it only makes sense to access the comments through the  
post to which they are attached. In the case of the blog you _could_  
do something like this in routes.rb:

map.resources :blogs do |blog|  
blog.resources :posts do |post|  
post.resources :comments  
end  
end

There are some very strong feelings out in the community about how  
deeply you should nest resources. As a practical matter it becomes a  
real pain in the neck to deal with things if you nest more than a  
level or two deep. Along those lines, you are allowed to create  
multiple entries in the routes.rb for each controller so you could  
break down the code above as follows:

map.resources :blogs do |blog|  
blog.resources :posts  
end

map.resources :posts do |post|  
post.resources :comments  
end

In either case you’ll have named routes along the lines of  
\<outer\_controller\>\_\<inner\_controller\>\_path …

blog\_post\_path(@blog, @post) – get to an individual post  
blog\_posts\_path(@blog) – get to the collection of posts for a  
particular blog

It’d also be completely acceptable from a REST perspective to consider  
the User and Group resources to include their habtm relationship.  
What I mean is that you could perfectly well create actions for  
add\_group, set\_group, and remove\_group to your UsersController if you  
find that simplifies things. In that case you would extend the route  
mapping with member functions (you specify the name followed by the  
http verb):

map.resources :users, :member=\>{:add\_group=\>:post,  
:remove\_group=\>:delete, :set\_group=\>:put}

HTH,  
AndyV  
On Apr 13, 10:35 am, Gregory S. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)