nested-comments

Nested Comments

Intro

A root comment can have up to 10 nested layers.

1. Comment A (root)
   └── 2. Reply to A
       └── 3. Reply to 2
            ...
            └── 10. Reply to 9

Instead of using recursion, I will build the feature using Stack and Map.

Table Design

CREATE TABLE IF NOT EXISTS comments (
    id UUID PRIMARY KEY,
    post_id UUID NOT NULL,
    user_id UUID NOT NULL,

    content TEXT NOT NULL,
    path VARCHAR(255), -- stack of its parents

    updated_at TIMESTAMP NOT NULL,
    created_at TIMESTAMP NOT NULL
);

Setting Up

1. Start all services:

make compose-all

2. Shutdown all services:

make compose-down

curl Sample

To keep it simple, I hardcoded the following ids in the script. Feel free to replace them:

• Post id: 01982686-4c00-7abe-826b-bf325c510b7b
• User id: 01982686-75ad-78ad-8587-d4c9815c5741

1. Create a comment layer 1

   curl -X POST http://localhost:3000/comments \
   -H "Content-Type: application/json" \
   -d '{
       "postId": "01982686-4c00-7abe-826b-bf325c510b7b",
       "userId": "01982686-75ad-78ad-8587-d4c9815c5741",
       "content": "This is a new comment"
   }'

2. Create a comment layer 2

   curl -X POST http://localhost:3000/comments \
   -H "Content-Type: application/json" \
   -d '{
       "postId": "01982686-4c00-7abe-826b-bf325c510b7b",
       "userId": "01982686-75ad-78ad-8587-d4c9815c5741",
       "content": "This is a comment layer 2",
       "path": "{comment layer 1 id}"
   }'

3. Create a comment layer 3

   curl -X POST http://localhost:3000/comments \
   -H "Content-Type: application/json" \
   -d '{
       "postId": "01982686-4c00-7abe-826b-bf325c510b7b",
       "userId": "01982686-75ad-78ad-8587-d4c9815c5741",
       "content": "This is a comment layer 3",
       "path": "{comment layer 2 path}/{comment layer 2 id}"
   }'

4. List comments by post

   curl -x GET http://localhost:3000/comments/post/01982686-4c00-7abe-826b-bf325c510b7b

   Response:

   [
       {
           "id": "019826d5-13b7-7788-935b-408bac22c8d2",
           "postId": "01982686-4c00-7abe-826b-bf325c510b7b",
           "userId": "01982686-75ad-78ad-8587-d4c9815c5741",
           "content": "This is a new comment",
           "createdAt": "2025-07-20T07:55:55.192Z",
           "updatedAt": "2025-07-20T07:55:55.192Z",
           "path": null,
           "replies": [
               {
                   "id": "019826d5-6a9b-7515-8025-e86b316f72fd",
                   "postId": "01982686-4c00-7abe-826b-bf325c510b7b",
                   "userId": "01982686-75ad-78ad-8587-d4c9815c5741",
                   "content": "This is a comment layer 2",
                   "createdAt": "2025-07-20T07:56:17.435Z",
                   "updatedAt": "2025-07-20T07:56:17.435Z",
                   "path": "019826d5-13b7-7788-935b-408bac22c8d2",
                   "replies": [
                       {
                           "id": "019826d6-f127-7268-ae69-cb56f047ded3",
                           "postId": "01982686-4c00-7abe-826b-bf325c510b7b",
                           "userId": "01982686-75ad-78ad-8587-d4c9815c5741",
                           "content": "This is a comment layer 3",
                           "createdAt": "2025-07-20T07:57:57.415Z",
                           "updatedAt": "2025-07-20T07:57:57.415Z",
                           "path": "019826d5-13b7-7788-935b-408bac22c8d2/019826d5-6a9b-7515-8025-e86b316f72fd",
                           "replies": []
                       }
                   ]
               }
           ]
       }
   ]