MongoDB Interview Questions
- What is MongoDB?
MongoDB is a popular NoSQL database that stores data in a document-oriented format.
- What are the advantages of using MongoDB?
Advantages of using MongoDB include flexible data modeling, scalability, high performance, and support for distributed systems.
- What is a document in MongoDB?
A document is a unit of data in MongoDB, which is similar to a row in a relational database.
- What is a collection in MongoDB?
A collection is a group of documents in MongoDB, similar to a table in a relational database.
- What is the difference between a document and a collection in MongoDB?
A document is a unit of data in MongoDB, while a collection is a group of documents.
- What is a primary key in MongoDB?
In MongoDB, the primary key is called the "_id" field. It is a unique identifier for each document.
- What is sharding in MongoDB?
Sharding is the process of distributing data across multiple servers or nodes in a distributed database system.
- How do you perform backups in MongoDB?
Backups in MongoDB can be performed using the "mongodump" and "mongorestore" utilities.
- What is indexing in MongoDB?
Indexing in MongoDB is the process of creating an index on a collection to improve query performance.
- What is the difference between a single-node and a replica set in MongoDB?
A single-node MongoDB deployment consists of a single server, while a replica set deployment includes multiple servers that are set up to automatically replicate data between them.
- What is a MongoDB query?
A MongoDB query is used to retrieve data from a collection in the database.
- What is aggregation in MongoDB?
Aggregation in MongoDB is the process of performing data analysis using various operations such as grouping, sorting, and filtering.
- What is a capped collection in MongoDB?
A capped collection is a fixed-size collection in MongoDB that automatically overwrites old data when the collection reaches its size limit.
- How do you handle transactions in MongoDB?
In MongoDB, transactions can be used to ensure atomicity, consistency, isolation, and durability of data changes.
- What is the maximum document size in MongoDB?
The maximum document size in MongoDB is 16 MB.
- What is a TTL index in MongoDB?
A TTL (Time To Live) index in MongoDB is used to automatically remove documents from a collection after a specified amount of time has elapsed.
- What is MapReduce in MongoDB?
MapReduce in MongoDB is a data processing technique used to process large amounts of data and return aggregated results.
- What is the difference between MongoDB and SQL?
MongoDB is a NoSQL database that stores data in a document-oriented format, while SQL is a relational database that uses tables to store data.
- How do you perform updates in MongoDB?
Updates in MongoDB can be performed using the "update" and "replaceOne" commands.
- What is the role of a MongoDB server?
The role of a MongoDB server is to store and manage data, handle client requests, and provide support for data querying and manipulation.
- What are the different types of data modeling techniques in MongoDB?
The different types of data modeling techniques in MongoDB include Embedded, Referenced and Hybrid.
- What is the purpose of the MongoDB ObjectId?
The MongoDB ObjectId is a unique identifier assigned to each document in a collection. It is automatically generated by MongoDB and ensures that each document has a unique identifier.
- What is the difference between MongoDB and Cassandra?
MongoDB is a document-oriented database that is primarily used for storing and managing unstructured data, while Cassandra is a wide column store that is used for managing structured data.
- What is the difference between MongoDB and Hadoop?
MongoDB is a database management system, while Hadoop is a distributed data processing platform. MongoDB is primarily used for storing and managing data, while Hadoop is used for processing large datasets.
- What is the role of a MongoDB cursor?
A MongoDB cursor is used to iterate through a set of results returned by a query. It provides a way to navigate through the results without loading them all into memory at once.
- What is the difference between a left join and an inner join in MongoDB?
In MongoDB, a left join returns all documents from the left collection and matching documents from the right collection, while an inner join returns only the matching documents from both collections.
- What is a covered query in MongoDB?
A covered query in MongoDB is a query that can be satisfied using only the index and does not require MongoDB to load the document into memory.
- What is the purpose of the $set operator in MongoDB?
The $set operator is used to update a specific field in a document without affecting the other fields.
- What is the purpose of the $push operator in MongoDB?
The $push operator is used to add an element to an array in a document.
- What is the difference between a unique index and a sparse index in MongoDB?
A unique index ensures that each document in a collection has a unique value for the indexed field, while a sparse index only indexes documents that have a value for the indexed field.
- What is the purpose of the $unwind operator in MongoDB?
The $unwind operator is used to separate an array field into multiple documents, one for each element in the array.
- What is a replica set in MongoDB?
A replica set in MongoDB is a group of servers that replicate data across multiple nodes for redundancy and high availability.
- What is the purpose of the $group operator in MongoDB?
The $group operator is used to group documents by a specific field and perform aggregation operations on the grouped data.
- What is a change stream in MongoDB?
A change stream in MongoDB is a real-time stream of changes to the data in a collection. It can be used to monitor changes and trigger events or alerts.
- What is the purpose of the $lookup operator in MongoDB?
The $lookup operator is used to perform a left outer join between two collections and return the matching documents from both collections.
- What is the purpose of the $addToSet operator in MongoDB?
The $addToSet operator is used to add a value to an array field in a document only if the value does not already exist in the array.
- What is the purpose of the $in operator in MongoDB?
The $in operator is used to match documents where the value of a field matches any value in a specified array.
- What is the purpose of the $geoNear operator in MongoDB?
The $geoNear operator is used to return documents that are near a specified point in a geospatial index.
- What is sharding in MongoDB?
Sharding in MongoDB is a technique used to partition data across multiple servers to improve performance and scalability.
- What is a capped collection in MongoDB?
A capped collection in MongoDB is a fixed-size collection that is automatically overwritten once it reaches its size limit. It is used to store temporary or log data.
- What is the purpose of the $text operator in MongoDB?
The $text operator is used to perform a full-text search on a collection and return documents that match the specified search term.
- What is the difference between find() and findOne() in MongoDB?
find() returns all matching documents for a query, while findOne() returns the first matching document.
- What is a gridFS in MongoDB?
GridFS in MongoDB is a way to store and retrieve large files and binary data such as images, videos, and audio files that exceed the BSON document size limit.
- What is the difference between update() and save() in MongoDB?
update() is used to update one or more fields in a document, while save() is used to replace an entire document.
- What is the purpose of the $match operator in MongoDB?
The $match operator is used to filter documents based on specified conditions before processing the data using other aggregation operators.
- What is the purpose of the $out operator in MongoDB?
The $out operator is used to write the results of an aggregation pipeline to a new or existing collection.
- What is the purpose of the $redact operator in MongoDB?
The $redact operator is used to restrict access to specific fields in a document based on a user's access level.
- What is the purpose of the $bucket operator in MongoDB?
The $bucket operator is used to group documents into buckets based on a specified expression and create a histogram.
- What is the difference between an index and a unique index in MongoDB?
An index in MongoDB is used to improve query performance, while a unique index ensures that each document has a unique value for the indexed field.
- What is the purpose of the $pushAll operator in MongoDB?
The $pushAll operator is used to add multiple elements to an array field in a document.
- What is the purpose of the $elemMatch operator in MongoDB?
The $elemMatch operator is used to match documents where a field contains an array of objects and at least one of the objects matches a specified condition.
- What is the purpose of the $addToSet and $each operators in MongoDB?
The $addToSet and $each operators are used to add multiple values to an array field in a document and ensure that the array does not contain duplicate values.
- What is the purpose of the $in and $nin operators in MongoDB?
The $in and $nin operators are used to match documents where the value of a field matches or does not match any value in a specified array.
- What is the difference between a database and a collection in MongoDB?
A database in MongoDB is a container for collections, while a collection is a container for documents.
- What is the purpose of the $exists operator in MongoDB?
The $exists operator is used to match documents where a specified field exists or does not exist.
- What is the purpose of the $sum operator in MongoDB?
The $sum operator is used to calculate the sum of a specified field for a group of documents.
- What is the difference between a query and a projection in MongoDB?
A query in MongoDB is used to specify the selection criteria for documents, while a projection is used to specify which fields to include or exclude from the query results.
- What is a MongoDB replica set?
A replica set in MongoDB is a group of MongoDB servers that maintain the same data set, providing high availability and automatic failover.
- What is the purpose of the $lookup operator in MongoDB?
The $lookup operator is used to perform a left outer join between two collections in MongoDB.
- What is an aggregation pipeline in MongoDB?
An aggregation pipeline in MongoDB is a framework for processing data using a sequence of stages that can filter, group, project, and sort data.
- What is the purpose of the $unwind operator in MongoDB?
The $unwind operator is used to deconstruct an array field in a document and output a document for each element in the array.
- What is the purpose of the $dateToString operator in MongoDB?
The $dateToString operator is used to convert a date field to a string representation in a specified format.
- What is a TTL index in MongoDB?
A TTL index in MongoDB is an index that automatically deletes documents after a specified time period.
- What is the difference between a primary key and a unique key in MongoDB?
A primary key in MongoDB is an automatically generated _id field that is unique for each document, while a unique key is an index on a user-specified field that ensures its values are unique.
- What is a covered query in MongoDB?
A covered query in MongoDB is a query that can be satisfied entirely using an index, without requiring the server to examine the actual documents.
- What is the purpose of the $geoNear operator in MongoDB?
The $geoNear operator is used to find documents in a collection that are nearest to a specified location.
- What is the purpose of the $graphLookup operator in MongoDB?
The $graphLookup operator is used to perform a recursive graph search in a collection to find related documents.
- What is the purpose of the $set operator in MongoDB?
The $set operator is used to modify the value of a field in a document.
- What is a covered index in MongoDB?
A covered index in MongoDB is an index that includes all the fields required for a query, so the query can be satisfied entirely using the index.
- What is the purpose of the $type operator in MongoDB?
The $type operator is used to match documents where a specified field has a specific BSON type.
- What is the purpose of the $group operator in MongoDB?
The $group operator is used to group documents in a collection based on a specified field or expression.
- What is the difference between a collection and a document in MongoDB?
A collection in MongoDB is a group of related documents, while a document is a single record that contains data.
- What is the purpose of the $elemMatch operator in a projection in MongoDB?
The $elemMatch operator in a projection in MongoDB is used to return the first matching element from an array field that meets the specified criteria.
- What is the purpose of the $slice operator in MongoDB?
The $slice operator is used to return a subset of elements from an array field in a document.
- What is the purpose of the $dateFromString operator in MongoDB?
The $dateFromString operator is used to convert a string to a date field in a specified format.
- What is the purpose of the $regex operator in MongoDB?
The $regex operator is used to perform a regular expression search on a string field in a document.
- What is a shard key in MongoDB?
A shard key in MongoDB is used to partition data across multiple servers in a sharded cluster.
- What is a compound index in MongoDB?
A compound index in MongoDB is an index that includes more than one field.
- What is the difference between a cursor and an array in MongoDB?
A cursor in MongoDB is a pointer to the result set of a query, while an array is a collection of documents that have been retrieved from the database.
- What is the purpose of the $text operator in MongoDB?
The $text operator in MongoDB is used to perform a full-text search on a text field in a collection.
- What is a capped collection in MongoDB?
A capped collection in MongoDB is a fixed-size collection that automatically overwrites older documents as new ones are added.
- What is the purpose of the $addToSet operator in MongoDB?
The $addToSet operator in MongoDB is used to add an element to an array field in a document, but only if the element does not already exist in the array.
- What is the difference between a join and a lookup in MongoDB?
A join in MongoDB is a process of combining data from two or more collections based on a common field, while a lookup is a process of performing a left outer join between two collections.
- What is the purpose of the $position operator in MongoDB?
The $position operator in MongoDB is used to specify the position of a substring in a string field for a text search.
- What is the purpose of the $inc operator in MongoDB?
The $inc operator in MongoDB is used to increment the value of a numeric field in a document.
- What is a secondary index in MongoDB?
A secondary index in MongoDB is an index that is created on a non-primary key field to improve query performance.
- What is the purpose of the $geoIntersects operator in MongoDB?
The $geoIntersects operator in MongoDB is used to find documents in a collection that intersect with a specified geometry.
- What is the purpose of the $exists operator in MongoDB?
The $exists operator in MongoDB is used to match documents where a specified field exists or does not exist.
- What is the purpose of the $merge operator in MongoDB?
The $merge operator in MongoDB is used to merge the results of a pipeline with an existing collection.
- What is the difference between a single-field index and a compound index in MongoDB?
A single-field index in MongoDB is an index that includes only one field, while a compound index includes more than one field.
- What is the purpose of the $min and $max operators in MongoDB?
The $min and $max operators in MongoDB are used to find the minimum and maximum values of a specified field in a collection.
- What is the purpose of the $sum operator in MongoDB?
The $sum operator in MongoDB is used to calculate the sum of the values of a specified field in a collection.
- What is the purpose of the $in operator in MongoDB?
The $in operator in MongoDB is used to match documents where a specified field has one of several values.
- What is the purpose of the $out operator in MongoDB?
The $out operator in MongoDB is used to write the results of a pipeline to a new collection.
- What is the purpose of the $sample operator in MongoDB?
The $sample operator in MongoDB is used to return a random sample of documents from a collection.
- What is the difference between a multi-document transaction and a single-document transaction in MongoDB?
A multi-document transaction in MongoDB is a transaction that involves multiple documents in one or more collections, while a single-document transaction involves only one document in a collection.
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