What is indexing in MongoDB and how it can improve query performance?

With MongoDB's indexing feature, we may select a particular field or set of fields from a collection's documents to be used as an index. Then, this index may be used to quickly find documents that match a specific query. For instance, if we frequently search for users in a user collection by their email address, we can speed up these searches by creating an index on the email field. Indexing can also be used to define the sort order of the documents in a collection or to apply unique constraints on a field.

Explain aggregation in MongoDB.

We can conduct operations on several documents using aggregation, including filtering, grouping, and data transformation. The architecture for carrying out these processes, known as the aggregation pipeline, was introduced in MongoDB as a more powerful and adaptable method of aggregating data than the earlier group function.

How can we merge two collections in MongoDB?

The aggregate method in MongoDB can be used to combine two collections. In particular, we may do a left outer join on the two collections using the $lookup operator as the pipeline's initial stage. Due to the use of a common field, we will be able to combine documents from the two collections, and the merged documents will have fields from both collections.

What is CORS and how does it relate to MongoDB?

Cross-Origin Resource Sharing is referred to as CORS. Web browsers use this security measure to prevent web pages from sending requests to domains other than the one that originally served them. When developing a web application that sends HTTP requests to a MongoDB server that is located on a separate domain, CORS is important in the context of MongoDB. In this instance, we must enable CORS on the MongoDB server in order for the browser to accept HTTP queries. Setting the —setParameter enableCors=true flag when the MongoDB server is started will accomplish this.