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Active Record Associations in Rails

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Deleting an Associated Record

3:04 with Jay McGavren

Our blog app now lets us create, read, and update Comments that belong to a Post. Lastly, we need to support deleting Comments.

Our blog app now lets us create, read, and update Comments that belong to a Post. Lastly, we need to support deleting Comments.

  • We can set up a delete link in the _comment.html.erb partial:

views/comments/_comment.html.erb

<div class="comment-admin">
  <%= link_to "Edit", edit_post_comment_path(@post, comment) %>
  <!-- NEW CODE BELOW -->
  <%= link_to "Delete", [@post, comment], method: :delete %>
</div>
  • We need a destroy action on the CommentsController:
  def destroy
    @comment = Comment.find(params[:id])
    @comment.destroy
    redirect_to @post
  end

Further Reading

Rails Guides: Nested Resources

Extra Credit

We currently have a before_action named set_post on the CommentsController. Try adding a second before_action named set_comment that sets the @comment instance variable.

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    Our blog app now let's just create, read, and update comments that belong to a post. 0:00
    Lastly, we're going to need to support deleting comments. 0:05
    We're going to want a delete link to appear right next to each comment here on 0:08
    our list. 0:12
    So we can add that by editing the comment partial. 0:13
    So we'll go here to our views comments, and we'll click on the comment partial, 0:17
    and here in our comment admin div we're going to add another link. 0:23
    Link_to, we're going to want this to have text of "Delete", and 0:27
    then we need to set up the path that our link is going to point to. 0:33
    This link is going to need to include ID's for the post and the comment. 0:38
    So we're going to do that by passing another array. 0:43
    We're going to pass @post instance variable, and the comment local variable. 0:45
    We're going to want to submit this link using the delete HTTP method. 0:53
    So we're going to add the method argument here, and 0:58
    we're going to pass that as symbol of delete. 1:01
    Save that, and go to our browser, and refresh, and here are our new delete 1:05
    links, but as you can see, there's no destroy action on the comments controller. 1:10
    We'll need to add that now, so we'll go to the comments controller, 1:15
    and we'll add a new method named destroy. 1:21
    First, we'll need to find the comment that we're getting rid of, 1:28
    and we'll assign it to the common instance variable, 1:34
    that'll be the result of Comment.find( params [:id]). 1:39
    It'll pull that from the link path. 1:44
    Then we need to actually get rid of that comment, 1:50
    we'll call @comment.destroy, and lastly, 1:53
    we're going to need to send the browser somewhere after we destroyed the comments. 1:55
    So we're going to make a comment to redirect_to @post. 2:00
    So let's save that. 2:07
    We'll go back to my post show view, and we'll click on the delete link again, and 2:09
    this time it calls the destroy action, deletes the comments, and 2:14
    redirects us back to the show post page. 2:18
    So now our users can create, read, update, and delete comments that belong to a post. 2:22
    In the first stage we showed you how to work with associated models in 2:27
    the console. 2:30
    In this stage we've shown you how to update your routes, controllers, and 2:31
    views to work with those same models. 2:34
    We've shown you the basics for incorporating an associated model into 2:37
    your rails app, but see the teacher's notes if you'd like to learn more. 2:41
    Hopefully now, you're really starting to see the usefulness of associations. 2:45
    They allow you to represent the relationships between your app's data 2:49
    in ways you couldn't before. 2:52
    We haven't see everything yet though. 2:54
    In the final stage of this course, we'll look at one more kind of association, and 2:56
    we'll see additional operations you can perform on associated models. 3:00

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