CRUD Challenges

Introduction

CRUD challenges sharpen the muscle memory you'll lean on every day. Each task targets a real production pitfall — upserts, optimistic concurrency, projections, soft deletes, bulk operations — so the patterns become second nature.

Understanding the topic

The 7 CRUD challenges in this lesson:

• 1. Idempotent signup with upsert + $setOnInsert.
• 2. Optimistic concurrency with version field.
• 3. Soft delete + restore endpoint.
• 4. Paginated list using cursor (_id beats skip).
• 5. Bulk import with insertMany + ordered:false.
• 6. Atomic counter using $inc + findOneAndUpdate.
• 7. Embed-or-reference decision for comments on a post.

Informative example

Challenge 2 — optimistic concurrency in one round-trip:

const res = await db.tasks.findOneAndUpdate(
  { _id, version: currentVersion },
  { $set: { title, updatedAt: new Date() }, $inc: { version: 1 } },
  { returnDocument: "after" }
);
if (!res) throw new ConflictError("task changed since you loaded it");

Best practices

• Implement every challenge twice — once naive, once optimal.
• Run explain("executionStats") on each and verify index usage.
• Time each operation with console.time(); you'll feel the difference.