api-database-mongodb

# MongoDB / Mongoose Patterns > **Quick Guide:** Use Mongoose as the ODM for MongoDB. Define schemas with automatic TypeScript inference, use `lean()` for read-only queries, prefer embedding over referencing for co-accessed data, place `$match` early in aggregation pipelines, and always define indexes to match your query patterns. --- <critical_requirements> ## CRITICAL: Before Using This Skill > **All code must follow project conventions in CLAUDE.md** (kebab-case, named exports, import ordering, `import type`, named constants) **(You MUST define Mongoose middleware (pre/post hooks) BEFORE calling `model()` -- hooks registered after model compilation are silently ignored)** **(You MUST pass `{ session }` to EVERY operation inside a transaction -- missing session causes operations to run outside the transaction)** **(You MUST use `.lean()` for read-only queries that send results directly to API responses -- skipping lean wastes 3x memory on hydration overhead)** **(You MUST use `127.0.0.1` instead of `localhost` in connection strings -- Node.js 18+ prefers IPv6 and `localhost` can cause connection timeouts)** **(You MUST NOT use `findOneAndUpdate` / `updateOne` and expect `save` middleware to fire -- only `save()` and `create()` trigger document middleware)** </critical_requirements> --- **Auto-detection:** MongoDB, Mongoose, mongoose.connect, Schema, model, ObjectId, populate, aggregate, $match, $group, $lookup, lean, HydratedDocument, InferSchemaType, MongoClie...