MongoDB Concepts 2

Related to Aggregatio Framework, which of the following are true?

• Only one expression per stage can be used.

• Some expressions can only be used in specific stages.

• When using only one stage, the shorthand syntax db.coll.aggregate({stage}) can be used.

• An aggregation pipeline is a list of stages.

Answer explanation

The correct answers highlight that some expressions are stage-specific and that an aggregation pipeline consists of multiple stages. The other statements are incorrect as they misrepresent the framework's capabilities.

Which of the following is true of the $match stage?

• It uses the familiar MongoDB query language.

• $match can use both query operators and aggregation expressions.

• $match can only filter documents on one field.

• It should come very early in an aggregation pipeline.

Answer explanation

The $match stage uses MongoDB's query language, allowing for complex queries. It is best placed early in the aggregation pipeline to reduce the number of documents processed in subsequent stages, improving performance.

Which of the following statements are true of the $project stage?

• Beyond simply removing and retaining fields, $project lets us add new fields.

• $project cannot be used to assign new values to existing fields.

• $project can only be used once within an Aggregation pipeline.

• Once we specify one field to retain, we must specify all fields we want to retain. The _id field is the only exception to this.

Answer explanation

The $project stage allows adding new fields and requires all fields to be specified for retention, except for the _id field. The other statements are incorrect.

What does it mean when we say that MongoDB follows a code-first approach?

• It allows you to use third-party frameworks to give you read and write operations.

• You can store unstructured data.

• There are no complex table definitions, so you can start writing your first data as soon as you connect to your MongoDB database.

• You’re ready to work on your database as soon as your table design is created.

Answer explanation

A code-first approach in MongoDB means you can start using the database immediately without complex table definitions, allowing for quick data entry as soon as you connect.

MongoDB documents of a similar type are grouped into _______________.

• A collection

• A cluster

• A replica set

• An index

Answer explanation

MongoDB documents of a similar type are grouped into a collection. This is the fundamental structure for organizing data in MongoDB, allowing for efficient data retrieval and management.

Fill in the blank. ___________ provided by MongoDB means as your data needs grow, you can partition your data.

• Replication

• Aggregation

• Projection

• Sharding

Answer explanation

Sharding provided by MongoDB allows you to partition your data across multiple servers, making it easier to scale as your data needs grow. This is essential for handling large datasets efficiently.

MongoDB is schema-less. What does that mean?

• MongoDB does not require that you create the schema and the table structures before writing the data.

• With MongoDB, you alter your tables to store additional fields.

• You can only store structured data in MongoDB.

• Create the table structures that will hold your data.

Answer explanation

MongoDB being schema-less means you don't need to define a schema or table structure before inserting data. This allows for flexibility in data storage, unlike traditional databases that require predefined schemas.

Which of the following are comparison operators in MongoDB? (Select all that apply.)

• $gte

• $lte

• $eql

• $lt

Answer explanation

In MongoDB, $gte (greater than or equal), $lte (less than or equal), and $lt (less than) are valid comparison operators. $eql is not a recognized operator in MongoDB.

Jenni works at an e-commerce start-up that uses MongoDB for its customer data management, product catalog and payment processing. Her startup now wants to add personalized recommendations for customers using real-time analytics. Jenni and her team will need to move data to a separate analytics database to handle this new use case.

• True

• False

Answer explanation

False is correct because MongoDB can handle real-time analytics and personalized recommendations without needing to move data to a separate analytics database.

You want to create a new membership tier for your bike-sharing service for users who take long trips. Using the trips collection in the sample_training database, you need to find the trips taken by subscribers with the longest trip durations. Return the top 5 results in descending order. To do this, which query should you use? (Select one.)

• db.trips.find({ usertype: "Subscriber" }, { sort: { tripduration: -1 } }, { limit: 5 });

• db.trips.find({ usertype: "Subscriber" }, { sort: { tripduration: 1 } }, { limit: 5 });

• db.trips.find({ usertype: "Subscriber" }).sort({ tripduration: 1 }).limit(5);

• db.trips.find({ usertype: "Subscriber" }).sort({ tripduration: -1 }).limit(5);

Answer explanation

The correct query is db.trips.find({ usertype: "Subscriber" }).sort({ tripduration: -1 }).limit(5); This retrieves trips by subscribers, sorts them by trip duration in descending order, and limits the results to the top 5.