Top MongoDB Interview Questions and Answers

 

Here are top MongoDB interview questions,

1. What is MongoDB?

MongoDB is a NoSQL document-oriented database that stores data in JSON-like documents.

 

2. What is a document in MongoDB?

A document is a basic unit of data in MongoDB. It is a JSON-like data structure composed of key-value pairs.

 

3. What is a collection in MongoDB?

A collection is a group of MongoDB documents. It is equivalent to an RDBMS table.

 

4. What is the difference between MongoDB and SQL databases?

MongoDB is a NoSQL database, while SQL databases are relational databases. MongoDB uses a flexible, document-based model, whereas SQL databases use tables and predefined schemas.

 

5. What is the primary key in MongoDB?

In MongoDB, the "_id" field serves as the primary key for a document. It must be unique within a collection.

 

6. How can you create a database in MongoDB?

A database is automatically created when you start adding data to it. You can use the "use" command to switch to a specific database, and MongoDB will create it if it doesn't exist.

 

7. How do you insert documents in MongoDB?

To insert documents in MongoDB, you can use the "insertOne()" or "insertMany()" methods. For example:

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db.collectionName.insertOne({ key: value });

db.collectionName.insertMany([{ key: value1 }, { key: value2 }]);

 

8. How do you query documents in MongoDB?

You can use the "find()" method to query documents in MongoDB. For example:

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db.collectionName.find({ key: value });

 

9. What is an index in MongoDB?

An index in MongoDB is a data structure that improves the speed of data retrieval operations. It can be created on a single field or a combination of fields.

 

10. How can you create an index in MongoDB?

To create an index, you can use the "createIndex()" method. For example:

db.collectionName.createIndex({ key: 1 });

 

11. How do you update documents in MongoDB?

You can use the "updateOne()" or "updateMany()" methods to update documents in MongoDB. For example:

db.collectionName.updateOne({ key: value }, { $set: { newKey: newValue } });

 

12. How do you delete documents in MongoDB?

To delete documents, you can use the "deleteOne()" or "deleteMany()" methods. For example:

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db.collectionName.deleteOne({ key: value });

 

13. What is aggregation in MongoDB?

Aggregation in MongoDB is a framework used to process and combine data from multiple documents, performing operations such as grouping, filtering, and calculating aggregates.

 

14. How do you perform aggregation in MongoDB?

You can use the "aggregate()" method to perform aggregation in MongoDB. It takes an array of stages that define the aggregation pipeline. For example:

db.collectionName.aggregate([

  { $match: { key: value } },

  { $group: { _id: "$field", total: { $sum: "$value" } } }

]);

 

15. What is sharding in MongoDB?

Sharding is a method of distributing data across multiple machines in a MongoDB cluster. It helps in horizontal scaling and improves performance and capacity.

 

16. How do you enable sharding in MongoDB?

To enable sharding, you need to use the "sh.enableSharding()" method and specify the database you want to shard. For example:

sh.enableSharding("databaseName");

 

17. What is replica set in MongoDB?

A replica set is a group of MongoDB servers that maintain the same data set. It provides redundancy and high availability by replicating data across multiple servers.

 

18. How do you create a replica set in MongoDB?

To create a replica set, you need to initialize the primary node and add secondary nodes using the "rs.initiate()" and "rs.add()" commands, respectively.

 

19. How does MongoDB ensure high availability and fault tolerance?

MongoDB achieves high availability and fault tolerance through features like replica sets, automatic failover, data replication, and built-in monitoring.

 

20. How can you monitor MongoDB performance?

MongoDB provides a variety of monitoring tools, including the MongoDB Management Service (MMS), which allows you to track performance metrics, set up alerts, and view real-time and historical data.

Above are few top MongoDB interview questions. Remember to prepare and expand on these answers.

Good luck with your interview!  👍