Nested Routes and Resources

4:31 with Jay McGavren

So far we've just relied on the show view for Posts to show a list of comments. That relies on an existing route for Posts. But to create, update, or delete comments, we're going to need a new set of routes, one that indicates which Post the Comment belongs to.

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So far we've just relied on the show view for Posts to show a list of comments. That relies on an existing route for Posts. But to create, update, or delete comments, we're going to need a new set of routes, one that indicates which Post the Comment belongs to.

If we were adding comments as a standalone model, we'd add a set of routes like these to config/routes.rb:

  get    '/comments',          to: 'comments#index', as: 'comments'
  post   '/comments',          to: 'comments#create'
  get    '/comments/new',      to: 'comments#new',   as: 'new_comment'
  get    '/comments/:id',      to: 'comments#show',  as: 'comment'
  get    '/comments/:id/edit', to: 'comments#edit',  as: 'edit_comment'
  patch  '/comments/:id',      to: 'comments#update'
  delete '/comments/:id',      to: 'comments#destroy'

But each comment belongs to a post.
When we ask to view a list of comments, we need to know which post we're getting comments for. So let's add a :post_id URL parameter in the route path, ahead of /comments.
By the way, the URL parameter is named :post_id to distinguish it from the Comment ID, which is named just :id.
So that it's clear that the start of the path is a Post ID, we'll add /posts to the start of the path also.
When we take a form submission to create a new comment, we'll need to know what post we're creating a comment for. So we'll add /posts/:post_id at the start of that path, too.
Basically, for every CRUD operation on comments, we're going to need to know what Post we're working with as well. So let'd copy /posts/:post_id and paste it in front of every route path for comments.

  get    '/posts/:post_id/comments',          to: 'comments#index', as: 'comments'
  post   '/posts/:post_id/comments',          to: 'comments#create'
  get    '/posts/:post_id/comments/new',      to: 'comments#new',   as: 'new_comment'
  get    '/posts/:post_id/comments/:id',      to: 'comments#show',  as: 'comment'
  get    '/posts/:post_id/comments/:id/edit', to: 'comments#edit',  as: 'edit_comment'
  patch  '/posts/:post_id/comments/:id',      to: 'comments#update'
  delete '/posts/:post_id/comments/:id',      to: 'comments#destroy'

These route names will give us path helper methods like comments_path, new_comment_path, etc.
But the paths also need a Post ID now, so we'll need to provide a Post each time we call a helper method.
Let's update the route names to reflect this. We'll add the word post_ before comment in each.

  get    '/posts/:post_id/comments',          to: 'comments#index', as: 'post_comments'
  post   '/posts/:post_id/comments',          to: 'comments#create'
  get    '/posts/:post_id/comments/new',      to: 'comments#new',   as: 'new_post_comment'
  get    '/posts/:post_id/comments/:id',      to: 'comments#show',  as: 'post_comment'
  get    '/posts/:post_id/comments/:id/edit', to: 'comments#edit',  as: 'edit_post_comment'
  patch  '/posts/:post_id/comments/:id',      to: 'comments#update'
  delete '/posts/:post_id/comments/:id',      to: 'comments#destroy'

With those changes made, bin/rails routes outputs:

           Prefix Verb   URI Pattern                                 Controller#Action
    post_comments GET    /posts/:post_id/comments(.:format)          comments#index
                  POST   /posts/:post_id/comments(.:format)          comments#create
 new_post_comment GET    /posts/:post_id/comments/new(.:format)      comments#new
     post_comment GET    /posts/:post_id/comments/:id(.:format)      comments#show
edit_post_comment GET    /posts/:post_id/comments/:id/edit(.:format) comments#edit
                  PATCH  /posts/:post_id/comments/:id(.:format)      comments#update
                  DELETE /posts/:post_id/comments/:id(.:format)      comments#destroy

Putting /posts/:post_id in each path and post_ in each route name is a lot of repetition.
Instead, we can nest the routes under the :posts resource.
Nesting routes under a resource will add an ID parameter for that resource to the start of each nested route's path.
So nesting under the :posts resource will automatically add /posts/:post_id to the start of each comment route. We can remove /posts/:post_id from the start of each nested path.
Nesting under a resource will also add its name to the start of each nested resource name. So we can remove post_ from each route name.

  resources :posts do
    get    '/comments',          to: 'comments#index', as: 'comments'
    post   '/comments',          to: 'comments#create'
    get    '/comments/new',      to: 'comments#new',   as: 'new_comment'
    get    '/comments/:id',      to: 'comments#show',  as: 'comment'
    get    '/comments/:id/edit', to: 'comments#edit',  as: 'edit_comment'
    patch  '/comments/:id',      to: 'comments#update'
    delete '/comments/:id',      to: 'comments#destroy'
  end

Just as we replaced 7 Post routes with resources :posts in an earlier course, we can replace these 7 Comment routes with resources :comments.

  resources :posts do
    resources :comments
  end

Because resources :comments is nested within the :posts resource, every Comment route path still has /posts/:post_id at the start.
And every Comment route name includes post_

0:00
So far, we've just relied on the showView for post to show a list of comments.
0:05
That relies on an existing route for posts.
0:08
But to create, update, or delete comments, we're going to need a new set of routes.
0:12
One that indicates which post a comment belongs to.
0:16
If we were adding comments as a standalone model, we'd add a set of routes like
0:20
these to routes.rb, but each comment belongs to a post.
0:25
When we ask to view a list of comments,
0:27
we need to know which post we're getting comments for.
0:30
So let's add a post ID URL parameter in the route path, instead of /comments.
0:36
So let's add a post_id URL parameter in the route path, ahead of /comments.
0:41
By the way, this URL parameter is named post_id
0:44
to distinguish it from the comments ID, which is named just id.
0:49
So that it's clear that the start of the path is post_id,
0:52
we'll add /post to the start of the path, also.
0:55
When we take a form submission to create a new comment,
0:58
we'll need to know what post we're creating a comment for.
1:01
So we'll add /posts/post_id to the start of that path as well.
1:08
Basically, for every create operation on comments,
1:11
we're going to need to know what post we're working with as well.
1:14
So let's copy /posts/:post_id, and
1:17
paste it in front of every route path for comments.
1:21
These route names will give us path helper methods like comments path,
1:24
new comment path, etc.
1:27
But the paths also need a post ID now, so we'll need to provide a post each time
1:32
we call a helper method, let's update the route names to reflect this.
1:36
So we'll say, post_comments, new_post_comment,
1:42
post_comment, and edit_post_comment.
1:47
Let's save this, and if we go to our terminal and run bin/rails routes,
1:55
We'll see this result, here are the new routes for comments.
2:01
Putting a /posts/:post_id at the start of each route path is a lot of repetition.
2:08
Instead, we can nest the routes under the post resource.
2:11
So let's go through, let's find each instance
2:16
of /posts/:post_id, and let's replace it with nothing.
2:28
Nesting routes under a resource will add an ID parameter for
2:31
that resource to the start of each nested browse path.
2:34
So nesting them will basically give us the same result we had before,
2:38
without the repeated code.
2:39
Nesting under the post resource will automatically post/post_id to
2:44
the start of each comment route.
2:46
That's why we were able to remove post/post_id from the start of each
2:50
nested path.
2:52
We nest routes under a resource by adding a block to the call
2:57
to resources, so we'll say do end here.
3:00
And then we'll cut all this code out of here, and paste it inside the block.
3:06
Make sure to indent it so it lines up neatly.
3:10
Nesting under a resource will also add its name to the start of each nested
3:14
resource name.
3:15
So we can remove post_ from each route name here.
3:25
If we run bin/rails routes again,
3:29
we'll see that we get an almost identical set of routes.
3:34
Here at the start of each path is /posts/:post_id,
3:39
and here's post_ in each route name.
3:43
We got the same result with much less code.
3:47
But just as we replaced seven post routes with resources :posts
3:51
in an earlier course, we can replace these seven comment routes with one line.
3:57
Resources, comments, save this, and
4:01
run bin/rails routes again.
4:05
And with that one line of code we get a nearly identical result.
4:10
Because resources :comments is nested within the posts resource,
4:14
every comment route path still has post/:post_id at the start.
4:19
And every comment route name includes post_.
4:22
This set of routes is going to help us determine the post we're working with
4:26
when we create, update, or delete a comment on it.
4:29
We'll take care of comment creation next.

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