Mongodb

MongoDB

MongoDB is a document database. It stores data in JSON-like documents (BSON). It is the most popular NoSQL database, known for flexibility and scalability.

When to Use

• Rapid Prototyping: Schema-less design allows iterating fast without migrations.
• Content Management: Storing diverse assets with varying metadata.
• Catalogs: Product catalogs where each product has different attributes (size, color, wattage).

Quick Start

// Using Mongoose (Node.js)
const kittySchema = new mongoose.Schema({
  name: String,
});
const Kitten = mongoose.model("Kitten", kittySchema);

const silence = new Kitten({ name: "Silence" });
await silence.save();

Core Concepts

Documents (BSON)

Data is stored in "documents" (JSON objects) inside "collections" (Tables). { "_id": 1, "name": "Apple", "price": 10 }

Embedded Data vs References

• Embed: Store related data inside the document for fast reads. (e.g., Comments inside a Post).
• Reference: Store the ID and look it up ($lookup) for many-to-many relationships.

Sharding

MongoDB scales horizontally by splitting data across multiple servers (shards) based on a "shard key".

Best Practices (2025)

Do:

• Use Version 8.0+: For performance gains in time-series and queryable encryption.
• Index Early: "Compass" (GUI) or "Atlas Performance Advisor" will tell you when you miss indexes.
• Limit Array Growth: Don't use unbounded arrays (e.g., logging every login in the user document).

Don't:

• Don't join everything: MongoDB supports $lookup (JOINS), but overuse kills performance. Embed data if accessed together.
• Don't ignore Document Size: Max document size is 16MB.

References

• MongoDB Manual
• MongoDB University