Test 2 Study Guide

The second test of the course covers Module 2: Working with Databases. You can review the material on the following pages:

• Working with Databases (Overview)
• Introduction to NoSQL
• Introduction to MongoDB
• CRUD Operations
• MongoDB with Node.js
• Data Modelling and Queries

Key Concepts

In addition to reviewing the content above, you should feel comfortable answering the following questions:

• What is the difference between a SQL database and a NoSQL database?
• What are the three levels of organization in MongoDB (from largest to smallest)?
• What is an ObjectId, and what is the _id field used for?
• What is the difference between find and findOne? What does findOne return if nothing matches?
• What does a query filter do, and what happens when you pass multiple fields in a single filter?
• What does each of the following update operators do: $set, $unset, $inc, $push, $pull?
• What happens if you pass a plain object to updateOne without using an update operator like $set?
• Why do database operations in Node.js require async and await?
• What is the purpose of try/catch/finally when working with database code? Why is finally a good place to close the connection?
• How does find() behave differently in Node.js compared to the Mongo shell? What method do you call to get the results as an array?
• What is the difference between embedding and referencing when designing a document schema? Give an example of when each is appropriate.
• Write a query that finds all documents where a numeric field is greater than a given value.
• What is the difference between $and and $or? When do you need explicit $and versus relying on implicit $and?
• What do sort, limit, and skip do? How can they be combined for pagination?
• What is projection, and why would you use it?