Node.js + MongoDB Comments/Subcomments Implementation Method

Your question is about one-to-many relationship.

One post can have multiple comments and each comment can have multiple comments. However, one comment does not have multiple posts, and likewise, one comment cannot have multiple comments and sub-comments. So if you refer to the official document or these articles, you can roughly organize them like this.

/* Strategy */
{
  _id: 102,
  comment: "You know..."
  /* Skipping */
  subcomments: [103, 105, 111, 156] /* comments processed as subcomments._ids */
},
{
  _id: 103,
  comment: "ㄴLOL",
  /* Skipping */
  subcomments: null /* If there are no subcomments or deleted, remove the key or null */
},
/* Skipping */