20 Mongoose Interview Questions and Answers

Mongoose is a popular web development framework that helps developers create and manipulate data in MongoDB databases. If you’re applying for a position that involves web development, it’s likely that you’ll be asked Mongoose-related questions during your interview. In this article, we review some of the most common Mongoose questions and provide tips on how to answer them.

Mongoose Interview Questions and Answers

Here are 20 commonly asked Mongoose interview questions and answers to prepare you for your interview:

1. What is Mongoose?

Mongoose is a MongoDB object modeling tool designed to work in an asynchronous environment. Mongoose supports both promises and callbacks.

2. Can you explain how to connect to a MongoDB using Mongoose?

In order to connect to a MongoDB using Mongoose, you will need to first install the Mongoose npm package. Once you have done that, you can use the Mongoose.connect() function to connect to your MongoDB database.

3. Can you give me an example of how you would define a schema in Mongoose?

A schema in Mongoose is simply a representation of the structure of your data. For example, if you were creating a schema for a blog post, it might look something like this:

“`
var blogSchema = new mongoose.Schema({
title: String,
body: String,
date: { type: Date, default: Date.now },
comments: [{ type: mongoose.Schema.Types.ObjectId, ref: ‘Comment’ }]
});
“`

This schema defines a few key things about our data: that it will have a title and body (both strings), a date (with a default value of the current date and time), and an array of comments (which are ObjectIds that reference the Comment model).

4. How do the Schema and Model objects work together?

The Schema object contains information about the structure of the data in the collection, while the Model object contains functions that allow you to interact with the data in the collection.

5. How can we use mongoose models to create, read, update, and delete documents from our database?

We can use mongoose models to create, read, update, and delete documents from our database by using the model functions create(), find(), update(), and deleteOne().

6. How do we specify validation rules for data fields when defining our schema?

We can specify validation rules for data fields by adding validation keywords to the field definition in our schema. For example, we could add the “required” keyword to a field to make sure that it is always populated with a value.

7. In what situations is it best to use a Mongoose virtual field over a normal one?

A Mongoose virtual field is best used when you want to define a field that is not actually stored in the MongoDB database, but that you want to be able to access and manipulate as if it were a normal field. This can be useful for computed fields, or for fields that you want to be able to populate from an outside source.

8. What’s the difference between static methods and instance methods in Mongoose?

Static methods are methods that are called on the model itself, while instance methods are methods that are called on documents that are retrieved from the database. For example, you might have a static method on the User model called findByEmail that takes an email address and returns the user with that email address. An instance method might be one that returns the user’s full name.

9. What are some ways to validate Mongoose schemas?

There are several ways to validate Mongoose schemas. One way is to use the built-in validators that Mongoose provides, such as the “required” validator. Another way is to use custom validation functions. Finally, you can also use a third-party validation library like Validator.js.

10. What are middleware functions in Mongoose?

Middleware functions in Mongoose are functions that are run before or after certain operations are executed. For example, you could use a middleware function to run some code before a document is saved to the database. This would allow you to do things like validate the data or perform some other operation on it before it is actually stored.

11. How does Mongooe handle concurrency issues with multiple users writing to the same document?

Mongoose uses a technique called “optimistic concurrency” to handle this issue. What this means is that when a user tries to save a document that has been modified by another user, Mongoose will first check to see if the current version of the document in the database is the same as the version that the user started with. If it is, then the changes are saved. If it isn’t, then an error is thrown and the changes are not saved.

12. What is your opinion on the performance of Mongoose?

I believe that Mongoose is a great tool for creating quick and easy prototypes. However, for production applications, I believe that there are better options out there in terms of performance.

13. What are pre-hooks and post-hooks in Mongoose?

Pre-hooks and post-hooks are functions that are run before and after certain methods are called on Mongoose models, respectively. For example, you could use a pre-hook to encrypt a password before it is saved to the database, or use a post-hook to send a confirmation email after a new user is created.

14. Why should I use Mongoose over raw MongoDB queries?

Mongoose provides a schema-based solution to modeling your data, which means that you can define types and validations for your data that will be enforced when you try to insert or update documents. This can help to keep your data consistent and avoid errors. Additionally, Mongoose provides a number of helpful features, like pre- and post- hooks, that can make working with data easier.

15. What’s the difference between findOne() and findById()?

The findOne() function will return the first document that matches the query. The findById() function will return the document with the specified id.

16. Is it possible to have more than one model per collection with Mongoose? If yes then why would you want to do that?

Yes, it is possible to have more than one model per collection with Mongoose. There are a few reasons why you might want to do this:

– You might want to have different models for different purposes. For example, you might have a “User” model for storing information about users, and a “Post” model for storing information about posts.

– You might want to have different models for different parts of your application. For example, you might have a ” frontend” model for storing information that will be used in the frontend of your application, and a ” backend” model for storing information that will be used in the backend of your application.

– You might want to have different models for different versions of your application. For example, you might have a ” v1″ model for storing information about the first version of your application, and a ” v2″ model for storing information about the second version of your application.

17. Can you explain what populate() is used for in Mongoose?

The populate() method in Mongoose is used to automatically populate the referenced fields in a document with the data from the referenced document. This is useful when you want to retrieve data from multiple documents in a single query.

18. What is the purpose of $where in Mongoose queries?

The $where operator in Mongoose queries allows you to execute arbitrary JavaScript expressions to query for documents. This can be useful if you need to query for documents based on complex criteria that can’t be easily expressed using the other Mongoose query operators. However, you should be aware that using $where can be very slow, since it has to execute the JavaScript expression for every document in the collection.

19. Can you give some examples of common query operators in Mongoose?

Some common query operators in Mongoose are $gt (greater than), $lt (less than), $eq (equal to), $ne (not equal to), $in (in), and $nin (not in). These operators can be used to construct queries that filter documents based on specific criteria.

20. What are some tips to keep in mind while designing Mongoose Schemas?

1. Keep your schemas as simple as possible – only include the fields that you absolutely need.
2. Make use of Mongoose’s built-in features, like validation and typecasting.
3. Use virtuals to avoid duplication of data.
4. Use pre and post hooks to add extra functionality to your schemas.