MongoDB interview questions and answers

 1. What is MongoDB?

• MongoDB is a NoSQL database management system that uses a document-oriented data model. It stores data in flexible, JSON-like documents with dynamic schemas, making it easy to store and manage structured, semi-structured, and unstructured data.

2. What are the key features of MongoDB?

• Flexible Schema: MongoDB's schema-less design allows for dynamic and flexible data structures within the same collection.
• High Scalability: MongoDB supports horizontal scaling through sharding, allowing it to handle large volumes of data and high throughput.
• Replication: MongoDB supports replica sets, providing high availability and fault tolerance by maintaining multiple copies of data across different servers.
• Rich Query Language: MongoDB's query language supports a wide range of operations, including CRUD (Create, Read, Update, Delete), aggregation, indexing, and more.
• Geospatial Indexing: MongoDB has built-in support for geospatial indexing and querying, making it suitable for location-based applications.
• GridFS: MongoDB's GridFS allows for storing and retrieving large files, such as images and videos, in the database.

3. What is a document in MongoDB?

• A document in MongoDB is a JSON-like data structure composed of field-value pairs. It is analogous to a row in a relational database, but with a more flexible schema. Documents are stored in collections and can vary in structure from one document to another within the same collection.

4. How do you query data in MongoDB?

• Data in MongoDB is queried using the find() method, which returns a cursor to the result set. Queries can specify conditions using query operators like $eq, $gt, $lt, etc. For example:

  mongodb
  db.collection.find({ field: { $eq: value } })
  

5. What is a collection in MongoDB?

• A collection in MongoDB is a grouping of MongoDB documents. It is analogous to a table in a relational database. Collections do not enforce a schema, so documents within the same collection can have different structures.

6. What is sharding in MongoDB?

• Sharding in MongoDB is the process of distributing data across multiple machines to improve scalability and performance. It involves partitioning data into chunks and distributing these chunks across multiple shards (servers). MongoDB's sharding architecture allows it to handle large volumes of data and high throughput by distributing the load across multiple servers.

7. How do you perform aggregation in MongoDB?

• Aggregation in MongoDB is performed using the aggregate() method, which applies a sequence of operations to the documents in a collection. Aggregation operations include $match, $group, $sort, $project, $unwind, and more. For example:

  mongodb
  db.collection.aggregate([
      { $match: { field: value } },
      { $group: { _id: "$field", count: { $sum: 1 } } }
  ])
  

8. What is indexing in MongoDB?

• Indexing in MongoDB is the process of creating indexes on fields to improve query performance. Indexes allow MongoDB to quickly locate documents based on the indexed fields. MongoDB supports various types of indexes, including single-field indexes, compound indexes, multikey indexes, geospatial indexes, and text indexes.

9. What is replication in MongoDB?

• Replication in MongoDB is the process of synchronizing data across multiple servers to ensure high availability and fault tolerance. MongoDB uses replica sets, which consist of multiple MongoDB instances (nodes) organized into primary and secondary nodes. Data is replicated from the primary node to secondary nodes, providing redundancy and automatic failover in case of node failure.

10. How do you perform transactions in MongoDB? - MongoDB supports multi-document transactions starting from version 4.0 for replica sets and version 4.2 for sharded clusters. Transactions in MongoDB allow you to perform multiple operations on multiple documents in a single atomic operation, ensuring data consistency across multiple documents.

11. What is the MongoDB Atlas? - MongoDB Atlas is a fully managed cloud database service provided by MongoDB. It allows users to deploy, operate, and scale MongoDB databases in the cloud without the need for manual setup or management of infrastructure. MongoDB Atlas provides features such as automated backups, monitoring, and security controls.

12. How do you back up and restore data in MongoDB? - Data in MongoDB can be backed up using tools such as mongodump and mongorestore, which allow you to dump data from a MongoDB database to a binary format and restore it from the dump files, respectively. Additionally, MongoDB Atlas provides automated backups and point-in-time restores for databases deployed on the Atlas platform.