Top 30+ MongoDB Interview Questions and Answers [2021]

MongoDB Interview Questions and Answers

MongoDB Interview Questions and Answers: MongoDB is a document database that uses JSON documents to store data. It is based on the concept of documents and collections. In addition to scalability and redundancy, MongoDB can hold numerous databases and gives better performance. This MongoDB interview question is primarily intended to provide you a general sense of the kind of interview questions you might encounter.

Recruiters typically start with basic questions in interviews and gradually increase the difficulty level. So, in this MongoDB Interview Questions and answers blog, we’ll start with the basics and work our way up to more sophisticated questions. You can prepare for your MongoDB Interview Questions and Answers by using these hand-picked MongoDB interview questions.

MongoDB Interview Questions and Answers for Beginners

Table of Contents

What are the different languages that MongoDB supports?

MonggoDB supports C, C++, C#, Java, Node.js, Perl, PHP, Python, Ruby, Scala, Go, and Erlang as official drivers.

Any of the languages listed above can use MongoDB. There are a few other community-supported drivers as well, but the ones listed above are given by MongoDB.

What distinguishes MongoDB from the competition?

MongoDB is regarded as the best NoSQL database due to the following characteristics:

  • Document-oriented (DO)
  • Exceptional performance (HP)
  • High availability (HA)
  • Easy scalability
  • Rich query language

How does MongoDB handle transactions and locking?

MongoDB does not employ traditional locking with reduction because it is designed to be light, fast, and understandable. It can be thought as as a counterpart to MySQL’s MyISAM auto entrust sculpt. Performance is improved with the simplest business sustain, especially in a system with multiple servers.

To what extent and when does data become multi-slice?

MongoDB scrap is a collection of MongoDB scrap. As a result, a lump or mass is retained as an album of all substances. There will be more than a few slice data achievement choices only if there is an additional time slot, but when there are more than one lump, data is extended to a lot of slices and can be extended to 64 MB.

Examine MongoDB in comparison to Couchbase and CouchbaseDB.

Although MongoDB, Couchbase, and Couchbase DB are similar in many aspects, they differ in terms of model execution, crossing points, storage, and duplications, among other things.

What are the various NoSQL database types? Please give an example.

There are four basic types of NoSQL databases:

  • Key value store NoSQL database
  • Document store NoSQL database
  • Column store NoSQL database
  • Graph base NoSQL databse

There are a lot of NoSQL databases out there. NoSQL databases include MongoDB, Cassandra, CouchBD, Hypertable, Redis, Riak, Neo4j, HBASE, Couchbase, MemcacheDB, Voldemort, RevenDB, and others.

What’s the difference between MongoDB and MySQL, and how do you tell the two apart?

MongoDB Interview Questions and Answers: Despite the fact that MongoDB and MySQL are both free and open source databases, they differ significantly in terms of data representation, relationship, transaction, data querying, schema design and specification, performance speed, normalisation, and other factors. Comparing MySQL vs MongoDB is comparable to comparing relational and non-relational databases.

Is it possible to have a primary-key, foreign-key connection in MongoDB?

MongoDB does not allow main key-foreign key relationships by default.

Is a lot of RAM required for MongoDB?

No. MongoDB does not require a lot of RAM to run. Because it dynamically allocates and de-allocates RAM according to the requirements of the processes, it can run on a tiny amount of RAM.

In MongoDB, when do we utilize a namespace?

The namespace is utilized when the names of the database and collection are sequenced.

MongoDB Interview Questions and Answers for Intermediate

What is the best way to get an old file into the moveChunk directory?

When balancing the slices, the old files are converted to backup files and moved to the moveChunk directory once the functions are completed.

What is the significance of a query that is covered?

Because indexes are kept in RAM or sequentially on disc, a covered query makes query execution faster. It speeds up the execution of the query.

MongoDB can match the query condition as well as return the result fields using the same index without having to dig within the documents with a covered query because the fields are covered in the index itself.

What is MongoDB sharding?

Sharding is a MongoDB feature that allows you to store data records across many machines. It’s a MongoDB strategy to dealing with data growth. It divides data horizontally in a database or a search engine. A shard, often known as a database shard, is a partition.

What is MongoDB’s replica set?

A replica is a collection of mongo instances that share the same data set. One node in a replica set is primary, while the other is secondary. From primary to secondary nodes, all data is replicated.

What is the difference between a primary and secondary replica set in MongoDB?

Primary nodes in MongoDB are the nodes that may receive writes. Master nodes are another name for these. MongoDB replication is single master, which means that only one node can accept write operations at a time.

Slave nodes are second-level nodes. These are read-only nodes that mirror the primary.

In MongoDB, what syntax is used to build a Collection?

The following syntax can be used to build a collection in MongoDB:

db.createCollection(name,options)

In MongoDB, what syntax is used to dump a Collection?

To drop a collection in MongoDB, use the following syntax:

db.collection.drop()

What exactly is CRUD?

CRUD operations are available in MongoDB:

  • Create
  • Read
  • Update
  • Delete

What factors should be considered when developing a schema in MongoDB?

The following points must be considered:

  • Create a schema that meets the needs of your users.
  • If you’re going to use multiple items together, combine them into a single document. Separate them if necessary.
  • Do joins when you’re writing, not when you’re reading.
  • Optimize your schema for the most common use cases.
  • In the schema, perform sophisticated aggregation.

What is the function of the profiler in MongoDB?

The MongoDB database profiler displays the performance characteristics of each database operation. Using the profiler, you can identify queries that are slower than they should be.

Advance MongoDB Interview Questions and Answers

What are the Sharded cluster’s components?

The following are the components of a sharded cluster:

  • Shards
  • Query routers
  • Config servers

What is the command for creating a database?

The Database Name command can be used to create a database.

What’s the difference between Cassandra and MongoDB?

The following are the differences between MongoDB and Cassandra:

  • Cassandra is a high-performance distributed database system, while MongoDB is a cross-platform document-oriented database system.
  • Cassandra is written in Java, while MongoDB is written in C++.
  • In the event of a failure, MongoDB is simple to manage, whereas Cassandra delivers high availability with no single point of failure.

What is MongoDB’s purpose?

For operational requirements with live needs, we typically employ MongoDB as the primary data storage. MongoDB is suited for around 80% of the apps that we design nowadays. MongoDB is simple to use and extends in ways that are difficult to achieve with traditional databases.

MongoDB excels in a variety of use cases where relational databases fall short, such as semi-structured and structured applications, as well as large scalability requirements and multi-datacenter deployments.

MongoDB isn’t appropriate for all applications. Complex transactional applications and scan-based apps that read enormous portions of data, for example, are not ideal for MongoDB.

Product catalogues, mobile apps, content management, real-time personalization, and applications that provide individual perspectives across several systems are all examples of common MongoDB applications.

What is the procedure for starting a MongoDB instance or server?

  • To start the MongoDB Server, we must follow the procedures below:
  • To begin, open a command line and type “mongod.exe” into it.
  • On the other side, we proceed to the path where MongoDB was installed.
  • To run the file, navigate to the bin folder, find the “mongod.exe” file, and double-click it.
  • We can connect to MongoDB using the Shell by going to the folder “C: MongoDB/bin” and typing mongo.

What is Capped Collection and how does it work?

MongoDB Interview Questions and Answers Must Read this question: The Capped collection is a unique type of collection in MongoDB. This means that the collection size can be limited in this collection. Capped Collection has the following syntax:

The following fields are available in the Capped Collection syntax:

Collection Name: This field is the name of the capped collection that we construct.

Capped: Capped is a boolean field that is true if a capped collection is created. Its value is false by default.

auto indexed: This is a boolean flag that controls whether or not auto-indexing is performed. Indexes will be constructed automatically if this flag is set to true. Indexes will not be built automatically if the flag is set to false.

Size: It refers to the maximum number of documents that can be stored in bytes. In the context of capped collections, it is a necessary field.

Max: The maximum number of documents that can be collected is represented by this parameter.

What does oplog (operational log) mean?

The operational log (oplog) is a specific type of restricted collection that keeps track of all operations that alter the data in our databases. Initially, it applies all database operations to the primary and then logs these activities on the primary’s oplog. The secondary members then reproduce and apply the asynchronous process’ operations.

In MongoDB, how do we execute Join operations?

The Join procedure is available in MongoDB3.2. The left outer join is the same as the new $lookup operator supplied with the aggregation pipeline. Example:

{
   $lookup:
     {
       from: <collection to join>,
       localField: <field from the input documents>,
       foreignField: <field from the documents of the "from" collection>,
       as: <output array field>
     }
}

In a Javascript Array, how can we retrieve MongoDB databases?

To obtain the existing databases, use “Show DBS” in the MongoDB console. We run the following code to obtain the MongoDB databases programmatically:

use admin
dbs = db.runCommand({listDatabases: 1})
dbNames = []
for (var i in dbs.databases) { dbNames.push(dbs.databases[i].name) }
Hopefully this will help someone else.
The below will create an array of the names of the database:
var connection = new Mongo();
var dbNames = connection.getDBNames();

What is the best way to update the object in the Nested Array?

The object is updated by running the following code:

Skip code block
{
“_id” : ObjectId(“4faaba123412d654fe83hg876”),
“user_id” : 123456,
“total” : 100,
“items” : [
{
“item_name” : “my_item_one”,
“price” : 20
},
{
“item_name” : “my_item_two”,
“price” : 50
},
{
“item_name” : “my_item_three”,
“price” : 30
}
]

Conclusion

The questions are categorized into three levels so that you can easily move from basic concepts to the most advance ones. The above compiled list of frequently asked questions will help you get through the interview confidently. Do not forget to go through the basic concepts of MongoDB before moving forward with these MongoDB Interview Questions and Answers.

Terry White

Terry White is a professional Drupal & WordPress developer, Web developer, Web designer, Software Engineer, and Blogger. He strives for pixel-perfect design, clean robust code, and a user-friendly interface. If you have a project in mind and like his work, feel free to contact him

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