This chapter introduced MongoDB CRUD operations and the behavior of common query and update operators.

Before moving forward, make sure you can explain and use:

• insertOne() and insertMany().
• Ordered and unordered insertion behavior.
• find() and findOne().
• Comparison operators such as $gt, $gte, $lt, $lte, $in, and $nin.
• Logical operators such as $and, $or, $nor, and $not.
• Projection and its inclusion/exclusion rules.
• updateOne() and updateMany().
• Update operators such as $set, $unset, $inc, $mul, $rename, and $currentDate.
• Array update operators such as $push, $addToSet, $pull, $pop, and $pullAll.
• Nested-document updates using dot notation.
• The difference between modifier updates and replaceOne().
• Upserts and $setOnInsert.
• deleteOne() and deleteMany().
• findOneAndUpdate() and related find-and-modify operations.
• Write result counts, duplicate-key errors, validation errors, and ambiguous network failures.
• Document-level atomicity and multi-document transactions.

Final assessment

Create a collection for an online learning platform. Each course should include an identifier, title, level, category, price, publication state, tags, instructor information, and creation date.

Implement the following operations:

1. Insert at least five courses.
2. Retrieve published courses in descending creation order.
3. Find courses in a specified price range.
4. Return only the title and instructor name.
5. Find courses containing a specified tag.
6. Update one course's price and update time.
7. Increment enrollment counts atomically.
8. Add a tag without introducing an equal duplicate value.
9. Update one nested instructor field without replacing the embedded document.
10. Create or update a settings document with an upsert.
11. Delete a selected practice course.
12. Explain how a unique index helps enforce a logical key.
13. Demonstrate the difference between a modifier update and a replacement.
14. Identify the risks of a broad update or delete filter.
15. Explain how you would handle a network timeout after a non-idempotent write.

Readiness criteria

You are ready for the next chapter when you can select the appropriate CRUD method, construct an accurate filter, choose the correct update operator, inspect write results, and explain the operation's atomicity and failure behavior.

Next chapter

Chapter 5 will cover advanced MongoDB query techniques, including array query operators, $elemMatch, $all, $size, $exists, $type, $expr, $regex, $text, $where considerations, geospatial filters, and combining complex conditions safely.