G1Joshi 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.