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Question

I would like to display nested comments in Flask. I use MongoDb and my document structure is like this:

{"_id":16,"content":"This is first answer.","discussion_id":1,
"posted":{"$date":"2017-10-26T19:19:05.174Z"}}
{"_id":17,"content":"This is second answer.","discussion_id":1,
"posted":{"$date":"2017-10-26T19:19:27.325Z"}}
{"_id":18,"content":"This is third answer.","discussion_id":1,
"posted":{"$date":"2017-10-26T19:20:00.126Z"}}
{"_id":19,"content":"This is fourth answer.  This answer's parent should be second.","discussion_id":1,
"posted":{"$date":"2017-10-26T19:21:28.206Z"},"parentid":2}
{"_id":20,"content":"Fifth answer whose parent should be fourth.","discussion_id":1,
"posted":{"$date":"2017-10-26T19:22:11.393Z"},"parentid":4}

Test python program looks like this:

from flask import render_template
from flask import Flask
from flask_pymongo import PyMongo

app = Flask(__name__)
app.config['MONGO_DBNAME'] = 'programming'
app.config['MONGO_URI'] = 'mongodb://localhost:27017/programming'
app.config['JSON_AS_ASCII'] = False
mongo = PyMongo(app)

@app.route('/')
def index():
    table = mongo.db.comments

    commentList = table.find({'discussion_id' : 1})

    comments = []
    for comment in commentList:
        comments.append({'commentnumber' : comment['_id'], 'date' : comment['posted'], 'content' : comment['content']})
        result = mongo.db.comments.find_one( { '_id' : comment['_id'] , "parentid": { '$exists': True, '$ne': False } })
        if (result):
            comments.append({ 'parent' : comment['parentid'] })
            print("Parent comment ", comment['parentid'])

    return render_template('index.html', comments=comments)

if __name__ == "__main__":
    app.run(debug=True)

And jinja template I would like to display comments recursively.

{%- for item in comments recursive %}
<li>{{ item.content }}</li>
{%- if item.children -%}
<ul class="children">{{ loop(item.children) }}</ul>
{%- endif %}</li>
{%- endfor %}

How should one store current post's children and display nested comments recursively in Jinja.

Answer 1

I did something similar on the forums for the Flask site for my game Infinitroid, eg https://infinitroid.com/forum/posts/12

What I basically did is, on the server side, use the parent-id of each comment to determine an integer depth or indent level: if you sort by primary key, then later comments come after eariler ones, and the parent should already be on the list. So you can set depth = 0 for comments with no parent, and parent.depth + 1 for those with a parent (use a temporary dictionary for lookup).

Set up your CSS to indent based on tag nesting level. And then, use the algorithm below for display. In my case I display the comments via javascript (you can view source on that page if you're curious) but the algorithm should be doable in Jinja too.

Start at depth=0. For each comment:

• if dropping a depth level, add closing tag for each level dropped
• add an opening tag for this comment and increment depth level
• display the comment body
• on the last comment, add closing tags for any remaining depth levels

You can structure this as a "loop with exit" loop to avoid duplicating the closing-depth-levels part.