Forem Issue Walkthrough: Comment Liquid Tags

I learned a lot from working on a Forem issue, where comments containing Comment Liquid Tags were rendered invalid if the tagged comment was later deleted.

Yes. That was a mouthful.

I created a walkthrough video sharing my troubleshooting process. If you would rather read, I have reproduced my process below the video image. 😊

Say Arit creates a comment, and then Bene creates their comment and includes a Liquid Tag to Arit's comment:

Next, Arit deletes her comment. When Bene goes to edit her comment containing the tag to Arit's now-deleted comment, she sees an error message. Also, the permalink to Bene's comment 404's.

Looking in the code, the app > liquid_tags > comment_tag.rb file initializes and renders the tagged comment. The app > views > comments > _liquid.html.erb file is the actual tagged-comment view.

Looking at the find_comment method in comment_tag.rb, we see that the error message raised by the exception matches what we see in the application:

def find_comment(id_code)
   Comment.find(id_code.to_i(26))
rescue ActiveRecord::RecordNotFound
   raise StandardError, "Invalid comment ID or comment does not exist"
end

Intuitively, I felt like a good solution would be to return a message like "Comment Not Found" within the Liquid Tag, while leaving the enclosing comment intact. But I was not sure how to bypass the error exception in order to accomplish this.

After a short tete-a-tete with my teammate Rhymes (🙏🏾), I learned a key difference between the .find and .find_by methods: if the record is not found, .find always raises an exception while .find_by returns nil.

By calling .find_by, I could then render different views in _liquid.html.erb, depending on whether the local comment variable (passed into the render method) existed.

def find_comment(id_code)
   Comment.find_by(id_code.to_i(26))
end

<div class="liquid-comment">
  <% if comment %>
    <div class="details">
      <a href="/<%= comment.user.username %>">
      ...
      ...
  <% else %>
    <div class="body">
      <p>Comment Not Found</p>
    </div>
  <% end %>
</div>

But when I tested my implementation, I got another error:

Unsupported argument type: 53 (Integer)

The only code I changed that accepts an argument was the find_comment method. I realized that .find_by requires me to specify which attribute to search by. Furthermore, the Comment.id_code attribute is a string, not an integer. So I made the appropriate corrections:

 def find_comment(id_code)
    Comment.find_by(id_code: id_code)
 end

Testing my local application, everything worked as expected 🎉:

Figuring out how to solve a certain coding problem is sometimes akin to detective work. 🔎 You use the clues provided in the codebase (or by other devs) to figure out what needs to be changed, and where.

I hope this was helpful to someone. 😄 Thanks for reading/watching!