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!

Cover Photo by Meghan Schiereck on Unsplash