Top MongoDB Interview Questions for 2025

Introduction to MongoDB

Now that you are here, you might have already come across our Best Programming Languages to Learn in 2024 Guide. Developers and designers for cloud-based applications are being hired based on their skills in solving problems. For this reason, it is very important that you at least learn one of the programming languages and master it.

Hopefully, this article will help you understand and remember the most commonly asked and frequently answered MongoDB interview questions and answers. Now, coming back to the subject,

What is MongoDB?

MongoDB is one of the most widely used document-type database management programs, which is used for building high-level internet applications. MongoDB is also an open-source NoSQL database that uses documents with an optional schema.

MongoDB is now most popular with development teams that use agile methodologies for document-based database Internet applications. Developers use MongoDB to write code in languages like Java, JavaScript, C, C++, and Python.

Being a cloud-native, document-based database service that works on the cloud and also supports AWS, MongoDB is one of the most widely accepted platforms by developers for building internet-based applications.

Here are a few MongoDB Interview Questions that will help you head your interviews confidently and clear any face-to-face interview with ease.

MongoDB Interview Questions for Fresher’s

1. In MongoDB, what are databases?

In MongoDB, sets of documents are called collections. MongoDB then groups these collections into a database that can be hosted by MongoDB, but it is restricted to spreading the data of collections across other databases. Some database titles of MongoDB are as follows:

→ Admin
→ local
→ config

 2. What does a MongoDB collection mean?

In MongoDB, "Collection" refers to the collective sets of documents or a group of documents. For a row in a relational database, if a document behaves as an analog in MongoDB, then the collection in MongoDB can be imagined as an analog table.

Collections are not required to be in the shape of a table. In fact, even within a single collection, documents can have any number of shapes since collections have dynamic schemas.

 3. In MongoDB, what exactly is a document?

In MongoDB, a document refers to a key order set that associates object values. A document in MongoDB can be represented with a map, hash, or dictionary. In JavaScript, a document is also represented as an object. And for retrying a document, passing a query filter returns documents and objects from collections that match the filter.

 4. What exactly is a Mongo Shell?

The Mongo Shell is a JavaScript interpreter interface to MongoDB, used to update data and perform administrative operations. Using Mongo Shells, arbitrator JavaScript program functions, inspection of instances, and other operations like exploring MongoDB can be performed.

 5. What function does the MongoDB profiler serve?

The functionality of a MongoDB database profiler is to collect and display detailed information about every database command executed against a running database instance.

6. Describe what a document and a collection in MongoDB are. 

In MongoDB, the fundamental data unit is a document. 

It's an internal BSON-stored object that resembles JSON and contains crucial value pairs. 

There may be layered structures and various fields in each document. 

As an illustration 

{

  _id: ObjectId("64fe1234567890abcdef1234"),

  name: "John Doe",

  age: 30,

  skills: ["JavaScript", "MongoDB"]

}

Collection 

→ A collection is a group of documents in MongoDB. 
→ It's similar to a table in relational databases, but schema-less. 
→ All documents in a collection are stored together and can be queried inclusively. 
→ Illustration: A user's collection may contain multiple documents like the one  over

7. What are TTL indicators, and how are They Used in MongoDB? 

TTL( Time To Live) indicators in MongoDB are special indicators that automatically remove documents from a collection after a certain period. They're generally used for data that needs to expire after a specific time, such as session information, logs, or temporary data. To  produce a TTL  indicator, you can specify the expiration time in seconds 

8. What is MongoDB's Approach to Data Consistency?

MongoDB offers a number of tools to guarantee data consistency:

Journaling: Write-ahead logging is used by MongoDB to preserve data integrity.

Write Concerns: It allows you to describe the amount of acknowledgment that you want MongoDB to provide for write operations (for example, primary-only acknowledgment or primary plus secondary acknowledgment).

Data consistency for read operations may be guaranteed by configuring read concerns, and replication guarantees data consistency across many nodes.

9. A project scope statement: what is it?

In terms of the PMBOK Guide, "The process of describing project scope, boundaries, and deliverables as a form of documentation is called a Project Scope Statement." Project restrictions, milestones, task descriptions, and other details pertaining to the project and its product scope are all included in this paperwork. A project scope statement not only enables project managers to monitor the project but also informs stakeholders of deliverables and modifications.

10. Which approaches are used in remote MongoDB deployments to manage data consistency?

There are several ways to attain data consistency in remote MongoDB deployments:

Read Preference: To manage which data is read, set read preferences.
Write Concern: To regulate the acknowledgment of write operations, use write concern levels.
Transactions: To guarantee consistency across documents, MongoDB allows multi-document transactions.

11. MongoDB charts are what?

One of MongoDB's new integrated tools for data visualization is called MongoDB Charts.

The greatest method for producing visuals with data from a MongoDB database is to use MongoDB Charts.

Using a programming language like Python or Java enables users to quickly express data from a database without writing code.

MongoDB Interview Questions for Intermediates

1. Explain the MongoDB indexes.

In MongoDB, there are special structures called indexes that hold a piece of the data set in a way that makes it simple to explore. The value of a particular field or group of fields is stored in the index in descending order according to the value of the field that is provided in the index.

2. Describe the GridFS feature in MongoDB.

A specification called GridFS explains how to separate files into pieces for storage and reassemble them for retrieval. The GridFS driver implementation is in charge of organizing and running the file storage activities. Both the chunks and the file's metadata are stored by default in two separate files called fs.files and fs.chunks.

3. Describe a covered query in MongoDB.

When the fields used for queries are part of the index used for the query and when the fields returned in the query result have the same index, such a query is called a "covered query."

4. How much RAM does MongoDB require?

Even a minimal amount of RAM can be used to run MongoDB. Based on the needs of other processes, MongoDB allocates and releases RAM in real time.

5. Does MongoDB support foreign key constraints?

No, MongoDB does not support such relationships.

6. What data types are supported in MongoDB documents? 

MongoDB supports a variety of BSON data types, which extend standard JSON types: 

String →Textual data. 
Number → Integer( int), Long( long), Double( double), Decimal( Decimal128). 
Boolean → true or false. 
Date → Stores date and time in UTC format. 
Array → List of values( can store mixed types). 
Object/ Bedded Document → Nested documents within a document. 
ObjectId → Unique identifier automatically generated for, id field. 
Null → Represents a null value. 
Binary Data → Stores double data like images or lines. 
Regular Expression → For pattern matching. 
Timestamp → Special internal type used for replication and sharding. 
Code/JavaScript  → Stores JavaScript law.

7. Explain the Concept of Write Concern and Its Significance in MongoDB 

Write Concern in MongoDB refers to the position of acknowledgment requested from MongoDB for write operations. It determines how many nodes must confirm the write operation before it's considered successful. Write concern situations range from "acknowledged" (default) to "unacknowledged," "journaled," and various "replica acknowledged" levels.

The significance of write concern lies in balancing between data continuity and performance. Advanced write concern ensures data is safely written to disk and replicated, but it may impact performance due to the added latency.. 

8. An explanation of MongoDB's Aggregation Framework

For processing and transforming data on documents in a collection, MongoDB's Aggregation Framework is an effective tool.

It operates by transferring documents via a pipeline with many stages, each of which applies a certain operation on the data, such as sorting, filtering, grouping, reshaping, and computing aggregations.

Developing intricate data conversions and analytics right within the database is made easier with this technology.

9. When does MongoDB use GridFS, and what is it?

GridFS is a MongoDB specification for storing and retrieving big files. It is employed when particular file parts need to be efficiently retrieved or when files are larger than the 16 MB BSON-document size restriction.

GridFS divides a big file into smaller pieces and saves each piece as a distinct document in the fs. files and fs chunks collections. Large files, like pictures, films, or extensive databases, may be stored and retrieved effectively because of this.

 Now onto advanced-level MongoDB interview questions

MongoDB Interview Questions for Professionals

1. A high-level comparison of SQL databases with MongoDB

Tables, rows, columns, and records are the different types of data that SQL databases hold. This data is kept in a predefined model that isn't very flexible for modern, rapidly expanding, real-world internet-based web applications. In divergence, MongoDB employs a flexible framework that is simple to change and expand.

2. What is the reason for the enormous size of MongoDB data files?

When you configure the server, MongoDB pre-allocates data files to save space and minimize file system fragmentation.

3. MongoDB Charts: What Are They?

Integrated into MongoDB, MongoDB Charts is a brand-new tool for visualizing data.

By leveraging data from a MongoDB database, MongoDB Charts provides the finest method for visualizing data.

Users can quickly visualize data from a database using this tool without having to write any code in a programming language like Python or Java.

MongoDB Charts is available in two alternative implementations:

MongoDB Charts PaaS (Platform as a Service)

MongoDB Charts Server

4. How does MongoDB define a replica set?

Replication is the process we employ to maintain exact duplicates of your data across several servers. All production deployments should use it. If something happens to one or more of your servers, replication will keep your application running and your data secure.

Using MongoDB, a replica set can be built for this kind of replication. A group of servers known as a "replica set" consists of a primary server, which accepts writes, and numerous secondary servers, which maintain copies of the primary server's data. A new primary can be chosen by the secondary from among themselves if the primary fails.

5. What are some utilities for backup and restore in MongoDB?

Functions for backup, restore, import, export, and other related operations are absent from the Mongo shell. But there is no need for complicated GUIs or coding labor because MongoDB has developed ways to achieve this. In order to do this, a number of utility scripts are available, which may be used to import or export large amounts of data from the database. Among these useful programs are:

→ mongoimport
→ mongoexport
→ mongodump
→ mongorestore

6. How to Handle Schema Design and Data Modeling in MongoDB? 

→ Schema design and data modeling in MongoDB involve defining how data is organized and stored in a document-  acquainted database. Unlike SQL databases, MongoDB offers flexible schema design, which can be both an advantage and a challenge. Crucial considerations for schema design include 

→ Embedding vs. Representing: Deciding whether to embed affiliated data within a single document or use references between documents. 

→ Document Structure Designing documents that align with operation query patterns for effective read and write operations. 

→ Indexing: Creating indicators to support query performance. 

→ Data Duplication Accepting some position of data duplication to optimize for read performance. 

→ Sharding: Designing the schema to support sharding if vertical scaling is needed.  

Example in javascript 

const session = client.startSession();

session.startTransaction();

try {

 db.collection1.insertOne({ name: "Alice" }, { session });

db.collection2.insertOne({ name: "Bob" }, { session });

session.commitTransaction();                                                                                                                                                                                                                                                                                                                                                    } catch (error) {

 session.abortTransaction();

} finally {

session.endSession();

}

7. How is data migration managed in a functional MongoDB environment?

Use tools similar to mongodump and mongorestore from MongoDB to transfer data in real time. These tools minimize downtime by enabling you to import and export data between clusters.

8. What characteristics does MongoDB have?

Indexing: It offers unique, compound, geographical, and full-text indexing capabilities in addition to supporting generic secondary indexes.

aggregate: It offers a framework for aggregate built on the idea of pipelines for data processing.

Types of special collections and indexes: Time-to-live (TTL) collections for data that ought to expire at a specific moment are supported.

File storage: Large files and file information may be stored using its user-friendly protocol.

Sharding: The technique of dividing data among devices is called "sharding."

 

Tips to prepare for MongoDB Interview Questions

1. Learn the Fundamentals of MongoDB

Make sure you fully understand the following fundamental ideas before beginning to answer MongoDB interview questions:

Documents and collections

JSON vs. BSON

Flexibility and Schema Design

CRUD (Create, Read, Update, Delete) operations

These fundamental subjects will be tested at the start of many MongoDB interview questions.

2. Engage in Practical CRUD Tasks

Practical expertise is highly valued by employers. Prepare responses to the following MongoDB interview questions:

Creating queries with find(), updateMany(), insertOne(), and so on.

Making use of sorting, filtering, and projection

To improve your practical abilities, consider working through activities on sites like LeetCode or MongoDB University.

3. Understand indexing well

MongoDB interview questions should be expected to pertain to:

Index types include text, geographic, multikey, single field, and compound.

How performance is enhanced by indexing

When indexes should not be used

Bonus points for discussing index intersection and covered searches.

Conclusion

This article has briefed you on all the necessary questions you will need for your MongoDB interview. This article contains all of the top 15 MongoDB interview questions and answers that one would require for a professional career designing web-based applications.

JavaScript experts also use MongoDB to implement soft and smooth processing for queries and commands run against an already running database.

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Sprintzeal provides comprehensive professional training courses in high-level programming languages for candidates all over the world, such as the JavaScript Certification Training Course and the Full Stack Developer Master Program.