The challenge of hiring a skilled MongoDB developer can determine the success of your data strategies. MongoDB developers have the expertise to help your team manage large volumes of unstructured data, facilitate rapid applications development and deliver real-time data unstructured solutions. These developers are critical for handling complex, scalable applications that drive business growth.
But, how do you effectively hire a MongoDB developer? In this article, I’ll share some of our strategies for finding, screening, and hiring MongoDB experts – including technical interview questions along with answers to help you identify the best candidates.
Understanding MongoDB
MongoDB is a NoSQL database that supports a document-oriented data model. This means that it stores and retrieves data through documents, graph databases, and key value stores, making it a flexible data model for easy scalability and is suitable for applications that have large amounts of diverse and dynamic data.
Why Hire a MongoDB Developer?
Currently, 12,105 live websites use MongoDB, including well-known companies like Forbes and Toyota. Why? Let’s review the main reasons why companies hire MongoDB developers to manage their data.
1. A MongoDB Developer can Store Unstructured Data in Large Volumes
MongoDB allows users to save a lot of data with little or no structure. This is important for things like a customer’s continually changing location or past purchases, which consistently grow.
Once you hire a MongoDB developer, they will be able to add different types of data without setting database limits. This flexibility is impossible to overstress if it’s necessary for you.
2. Quick Development
If you hire a MongoDB developer who is talented, they can frequently add, update, or delete data structures without wasting much downtime between the numerous versions. On the other hand, trying to modify a relational database will undoubtedly go more slowly.
The dynamic schemas in MongoDB help your developer’s ability to attempt to incorporate or change anything within the database quickly.
3. A MongoDB Developer can Efficiently Scale Your Database Architecture
This database’s built-in sharding solutions make it easy to spread data across on-site servers or in the cloud, enabling you to make the most of cloud computing.
How to Hire a MongoDB Developer? 6 Key Steps
MongoDB developers are specialists in handling NoSQL databases. Given that these roles are not as common as other technical roles, finding MongoDB experts can be more challenging. Here are some of our tips to help you trace your recruitment plan effectively:
1. Identify Specific MongoDB Experience
For technical roles like MongoDB, it’s key to be very specific about what skills and abilities you need your candidates to have.
Start by determining familiarity with specific versions of MongoDB, as new features and deprecations can impact your project’s compatibility and performance. Additionally, look for experience in optimizing MongoDB’s storage engine and query performance, which is key for high-load environments.
In this early stage, where you’re defining the skills and experience you’re looking for in candidates, it’s always useful to identify your negotiable and non-negotiable skills. In other words, what skills are fundamental to performing the job (non-negotiables), and which ones are beneficial for the role but not critical (negotiables).
2. Level Up Your Sourcing Techniques
For technical roles that require a different level of specialization, simply posting job ads is not the most effective strategy. You need to be more intentional with your sourcing techniques.
A useful strategy is checking for contributions in MongoDB’s open source projects or other public repositories. While not always users are looking for jobs, if you pitch them an interesting proposal, you might just land a great candidate who you’ve already seen their coding style and collaboration skills firsthand.
Additionally, partnering with technical recruiters can make your search much more effective. Rather than starting from scratch, recruiters have already curated networks of potential candidates, speeding up the process.
3. Conduct Scenario-Based Technical Screening
Anyone can answer technical generic questions. There are thousands of articles in Google about “MongoDB Interview Questions,” and while having the theory clear is key, you’re hiring a MongoDB developer because you need someone with enough knowledge to help you solve your different data needs, so focus on evaluating their skills with actual problems.
This usually goes two ways: you can choose hypothetical scenarios that can give you a grasp of how candidates would solve these problems, or you can go with scenarios your company has faced.
For this type of screening, you can consider conducting a pair programming session to see how candidates integrate with existing team dynamics and coding practices.
4. Review Their Past Projects
For advanced and specialized roles, I always recommend reviewing the impact of a candidate’s previous work. You can do this by going through their portfolios, or descriptions of past projects that allow candidates to demonstrate how their contributions have driven improvements or led to innovations.
Through these reviews, you can reveal details such as how they have scaled databases, and understand their thought process behind these decisions. You can also discuss more in detail about their experiences designing or optimizing databases and the impact these changes had.
5. Structure Technical Deep-Dive Interviews
When planning your interview questions, make sure that these are aligned with the specific skills and expertise you want to evaluate. Often, I’ve found that some companies resort to more generic questions that don’t really relate to the role they’re hiring for.
For example, when interviewing a senior-level MongoDB developer, tailor your questions to understand their knowledge of more advanced features such as transactions, index management, and aggregation pipelines. Additionally, explore their experience with cross-technology integration, such as how they have used MongoDB in conjunction with other tools and platforms, like Apache Kafka for stream processing or Elasticsearch for full-text search capabilities.
A more targeted approach will ensure that your interview assesses the skills you’re more interested in.
6. Don’t Forget About Soft Skills and Culture Fit
Cultural fit and soft skills are as important as tech skills. If a candidate has all the technical knowledge, but struggles to communicate or collaborate with the rest of the team, then this will probably lead to problems in the future.
To avoid this, make sure that your interviews also focus on behavioral and situational questions, where you can see firsthand how they handle conflict, teamwork, and pressure.
Questions about their past work experience can be useful, as can exercises like pair programming, as mentioned, or group interviews, to see how they work in a live environment.
15 Interview Questions to Vet MongoDB Developers
If you have an interview coming up and are still unsure what questions to ask, here are 15 MongoDB interview questions (with answers) that are useful when evaluating candidates.
1. What are the main advantages of using MongoDB over a traditional relational database?
MongoDB offers a flexible schema design which allows for quicker iteration and development. It’s highly scalable both horizontally and vertically, and it excels in handling large volumes of structured, semi-structured, and unstructured data. Its document model is more intuitive for developers and can align more directly with the data structures used in applications.
2. What is the Structure of ObjectID in MongoDB?
This returns a 12-byte ObjectId value that consists of:
- A 4-byte value representing the seconds since the Unix epoch,
- A 3-byte machine identifier
- A 2-byte process id, and
- A 3-byte counter, starting with a random value
3. How does MongoDB handle transactional data?
Since version 4.0, MongoDB has supported multi-document ACID transactions. This allows MongoDB to handle transactional data by grouping multiple operations on different documents into a single atomic operation, ensuring consistency and isolation even across distributed deployments.
4. Describe the working of an index in MongoDB.
Indexes in MongoDB store a small portion of the data set in an easy-to-traverse form. They improve the speed of search operations by allowing MongoDB to locate a document efficiently without scanning every document in a collection. Common index types include single-field, compound, multi-key, and text indexes.
5. Can you explain sharding in MongoDB and why it’s important?
Sharding in MongoDB is the process of distributing data across multiple machines. It is a method used to scale horizontally by dividing the data set and distributing the data over multiple servers. Sharding is crucial for dealing with very large data sets and high throughput operations, allowing MongoDB to provide better performance and storage capacity.
6. Given a collection of e-commerce order documents with fields for order_id, customer_id, amount, and date, write an aggregation pipeline to calculate the total sales and average sale amount per day.
db.orders.aggregate([
{
$group: {
_id: { $dateToString: { format: "%Y-%m-%d", date: "$date" } },
totalSales: { $sum: "$amount" },
averageSale: { $avg: "$amount" }
}
},
{ $sort: { _id: 1 } }
]);
7. Implement a MongoDB transaction in pseudo-code to update the inventory collection (decrease stock) and create a new order in the orders collection.
const session = db.getMongo().startSession();
session.startTransaction();
try {
db.inventory.updateOne(
{ productId: "xyz" },
{ $inc: { stock: -1 } },
{ session }
);
db.orders.insertOne(
{ productId: "xyz", quantity: 1, status: "confirmed" },
{ session }
);
session.commitTransaction();
} catch (error) {
session.abortTransaction();
throw error;
} finally {
session.endSession();
}
8. Write a brief plan for migrating a large dataset from a relational database to MongoDB, focusing on a table with historical user data.
The migration plan would involve:
- Extracting data from the relational database using a SQL SELECT query.
- Transforming the data into a JSON format suitable for MongoDB.
- Using a tool like mongoimport to load the data into MongoDB, possibly in batches if the dataset is very large.
- Testing the newly migrated data in MongoDB to ensure integrity and performance.
- Incrementally switching application queries from the SQL database to MongoDB.
9. Outline steps to secure a MongoDB database that contains sensitive user data.
- Enable authentication and use role-based access control to limit who can access what data.
- Use TLS/SSL to encrypt data in transit.
- Enable encryption at rest to protect data stored on disk.
- Regularly update MongoDB and its environment to keep security patches current.
- Implement auditing to monitor access and changes to the database.
10. Explain What Sharding is and Why it’s Useful
Sharding is “a method for distributing data across multiple machines.” It is used in MongoDB to support deployments with particularly large data sets and high throughput operations.
If you have a database system with large data sets or high throughput applications, these can put a strain on the capacity of a single server. Hire a MongoDB developer who knows a solution to this.
The two methods for addressing system growth are vertical and horizontal scaling.
Additionally, a sharded cluster consists of shard, mongos, and config servers:
- “Shard: Each shard contains a subset of the sharded data and can be deployed as a replica set.
- Mongos: The mongos acts as a query router, providing an interface between client applications and the sharded clusters.
- Config servers: Config servers store metadata and configuration settings for the cluster. As of MongoDB 3.4, config servers must be deployed as a replica set (CSRS).”
11. Is it Possible to Isolate Your Cursors From Intervening With the Write Operations? If so, how?
Yes. You use the snapshot() method on a cursor. This isolates the operation for a specific case by traversing the index on the _id field, guaranteeing that the query will only return each document once.
12. Explain Create Operations and Give an Example
Create or insert operations are similar to most other databases. They add a new document to a collection, and if the collection doesn’t currently exist, the insert operation will create it. You can either insert one or insert many documents into a collection via these methods:
db.collection.insertOne()
db.collection.insertMany()
Each insert operation in MongoDB targets a specific collection. Here’s an example:
db.users.insertOne({
name: "sue",
age: 26,
status: "pending"
});
13. Explain and Give an Example of the Update Operation
As their name implies, update operations modify existing documents in a collection. There are three different methods you can use to update documents:
- db.collection.updateOne()
- db.collection.updateMany()
- db.collection.replaceOne()
Hire a MongoDB developer who can give an example of any of these. We’ve decided to show how to use updateMany():
db.users.updateMany(
{ age: { $lt: 18 } },
{ $set: { status: "reject" } }
);
14. How do you ensure redundancy and high availability in MongoDB?
MongoDB uses replica sets to ensure redundancy and high availability. A replica set consists of multiple replica nodes, with one primary node that handles all write operations and multiple secondary nodes that replicate the primary data. This setup provides automatic failover and data redundancy, ensuring data is always available even if a server fails.
15. Explain the significance of the primary key _id in MongoDB
The _id field is a special field in every MongoDB document that acts as the primary key. It is unique for each document in a collection and ensures that every document can be uniquely identified. The _id field is indexed by default, which facilitates fast document retrieval.
Hire The Best Remote MongoDB Developer For Your Business with DistantJob
The key to hiring MongoDB developers is making an effective recruitment process that starts by clearly defining the skills and qualifications necessary for the role, followed by an interview process designed to identify the talent you need.
However, this is easier said than done, so if you’re looking for a shortcut to hire a MongoDB without wasting resources or time, you can contact us. We’ve helped companies hire highly skilled developers for the past 15 years. Our all-in-one model goes beyond merely finding and vetting candidates; we also support companies with comprehensive HR packages and services.
Want to know more? Let’s talk.
