Planned lessonMID-042-L07

Demo: building the reviews service on MongoDB

On This Lesson 3 topics

This lesson is planned. The outline below lists the topics it will cover. The full lesson has not been published yet.

In this lesson

build the reviews service with a ratings summary. Prepares MID-042-LAB1.

Draft outline details

Create the Review document and repository; add POST /products/{id}/reviews and GET for the latest 20.
Add the compound index { productId: 1, createdAt: -1 } and prove IXSCAN with explain.
Add GET /products/{id}/rating-summary using an aggregation ($match, $group average and count).
Run it against 100 000 seeded reviews; compare timings with and without the index.
Planned mistake: embed the review list inside a ProductReviews document; at a few thousand reviews updates slow down. Fix: one document per review and a separate summary.
Use Testcontainers with a MongoDB image for the integration test (verify image tag).

Where is the average computed?

Show answer

In the database, by the aggregation pipeline.

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