api-database-mongodblisted

# MongoDB Native Driver Patterns > **Quick Guide:** Talk to MongoDB through the official `mongodb` driver with no schema layer in between. Create ONE `MongoClient` per process and reuse it -- it owns the connection pool. Type collections with a generic: `db.collection<UserDoc>("users")`. Write operations return acknowledgements, never documents. `find()` returns a lazy cursor; stream it with `for await` instead of `toArray()` for anything unbounded. Put `$match` first in every pipeline so it can use an index. Verify indexes with `explain("executionStats")` rather than assuming. Transactions need a replica set, a session on every operation, and a callback that can safely run twice. --- <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 create exactly ONE `MongoClient` per process and reuse it -- the client owns a connection pool, so constructing one per request opens a new pool per request and exhausts the server's connection limit)** **(You MUST pass `{ session }` to EVERY operation inside a transaction -- an operation without it silently runs outside the transaction and is not rolled back)** **(You MUST write `withTransaction` callbacks to be safely re-runnable -- the driver retries them on transient errors, so any side effect outside the transaction happens more than once)** **(You MUST iterate or close every