Advanced Topics Hub

flowchart TB
    subgraph Advanced[Advanced MongoDB Topics]
        Tx[Transactions<br/>Multi-doc ACID]
        RS[Replica Sets<br/>High Availability]
        Shard[Sharding<br/>Horizontal Scaling]
        CS[Change Streams<br/>Real-time Changes]
        RW[Read/Write Concern<br/>Durability & Consistency]
        Perf[Performance & explain<br/>Query Optimization]
    end

    Advanced --> Practice[Production Readiness ✅]

    style Tx fill:#7c3aed,color:#fff
    style RS fill:#3b82f6,color:#fff
    style Shard fill:#059669,color:#fff
    style CS fill:#f59e0b,color:#fff
    style RW fill:#ec4899,color:#fff
    style Perf fill:#06b6d4,color:#fff
    style Practice fill:#10b981,color:#fff

// Handle duplicate key error
try {
  await User.create({ email: "existing@example.com" });
} catch (err) {
  if (err.code === 11000) {
    const field = Object.keys(err.keyValue)[0];
    throw new Error(`${field} already exists`);
  }
  throw err;
}

1. SCHEMA DESIGN
   ✅ Design schemas around your query patterns (query-first design)
   ✅ Embed data that's always accessed together
   ✅ Reference data that grows unboundedly

2. INDEXING
   ✅ Index every field used in find(), sort(), and $lookup
   ✅ Use compound indexes that match your queries (ESR rule)
   ✅ Use explain() to verify index usage

3. QUERIES
   ✅ Use projection — only return fields you need
   ✅ Use pagination (limit + skip or cursor-based)
   ✅ Put $match early in aggregation pipelines
   ❌ Avoid $where (JavaScript execution — very slow)

4. CONNECTIONS
   ✅ Use connection pooling (Mongoose does this by default)
   ✅ Set appropriate pool size for your app's concurrency

5. OPERATIONS
   ✅ Use bulk operations instead of loops
   ✅ Use $inc, $push instead of read-modify-write
   ✅ Use TTL indexes for auto-expiring data