Project: Blog With Comments

Introduction

This project builds a blog with posts, tags, and comments using MongoDB modeling choices from earlier chapters. You implement embedded comments and referenced comments side by side, add indexes for list queries, and expose read APIs with PyMongo or FastAPI.

Prerequisites

Project Goals

Feature	Notes
Post CRUD	title, slug, body, tags, published
Comments	embedded array or separate collection
List by date	sort `createdAt`, pagination
Lookup by slug	unique index on `slug`

Data Models

Approach A: Embedded Comments (One-to-Few)

javascript

Add comment with $push:

javascript

db.posts.updateOne(
  { slug: "mongodb-blog-project" },
  {
    $push: {
      comments: {
        author: "Bob",
        body: "Thanks!",
        createdAt: new Date()
      }
    }
  }
)

Approach B: Referenced Comments (Scale)

posts:

javascript

db.posts.insertOne({
  title: "Referenced Comments Post",
  slug: "ref-comments-post",
  body: "...",
  tags: ["scale"],
  published: true,
  createdAt: new Date()
})

comments:

javascript

db.comments.insertOne({
  postId: ObjectId("..."),
  author: "Carol",
  body: "Referenced comment.",
  createdAt: new Date()
})

Query comments for a post:

javascript

db.comments.find({ postId: post._id }).sort({ createdAt: 1 })

Indexes

javascript

db.posts.createIndex({ slug: 1 }, { unique: true })
db.posts.createIndex({ published: 1, createdAt: -1 })
db.comments.createIndex({ postId: 1, createdAt: 1 })

Explain list query:

javascript

db.posts.find({ published: true }).sort({ createdAt: -1 }).limit(10).explain("executionStats")

Expect IXSCAN, not COLLSCAN — Indexes chapter.

PyMongo: List and Add Comment (Referenced)

python

FastAPI Endpoints Sketch

Extend chapter 20 posts router:

python

Subset Pattern (Optional)

Homepage shows latest 3 comments embedded; full thread in comments collection — Common Modeling Patterns.

Post-Project Checklist

slug unique index enforced
Chose embedded vs referenced with written rationale
List query uses compound index on published + createdAt
explain shows index use

FAQ

Which comment model should I ship?

Embedded for < ~100 comments per post and single-document reads. Referenced when comments grow large or need independent moderation.

Soft-delete posts?

Add deletedAt and filter deletedAt: { $exists: false } — Delete and TTL.

Full-text search on posts?

Text index on title and body — Indexes.

Auth for posting?

Add JWT on write routes — FastAPI JWT.

Next project?

Product catalog uses dynamic attributes.