20 Firestore Interview Questions and Answers

When applying for a position that involves working with Firestore, it is important to be prepared for questions about the platform. Firestore is a popular database solution for mobile and web applications, and knowing how to answer questions about it can help you stand out from other candidates. In this article, we discuss some of the most common Firestore interview questions and how to answer them.

Firestore Interview Questions and Answers

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

1. What is Firestore?

Firestore is a cloud-based NoSQL database that can be used for storing and syncing data across multiple devices. It offers real-time updates so that changes made on one device are immediately reflected on all other devices that are connected to the database.

2. Can you explain the purpose of using an index in a Firestore collection?

An index is used in a Firestore collection to specify which fields in the collection should be searchable by Firestore’s built-in search functionality. By default, all fields in a Firestore collection are indexed, but you can remove fields from the index or add new fields to the index as needed.

3. What are composite indexes and why are they useful?

Composite indexes are indexes that combine multiple fields in an index. This can be useful when you need to query data based on multiple fields. For example, if you have a collection of users and you want to be able to query them by both their name and their age, you would need to create a composite index on those two fields.

4. Can you give me some examples of how you would use complex queries with Firestore?

There are many ways to use complex queries with Firestore, depending on your specific needs. For example, you might use a complex query to find all documents that contain a certain keyword, or to find all documents that were created within a certain time frame. You could also use a complex query to find all documents that are associated with a particular user.

5. Is it possible to query multiple collections or subcollections at once? If yes, then how?

Yes, it is possible to query multiple collections or subcollections at once in Firestore. This can be done by using the Collection Group Query feature. This feature allows you to run a query across all collections that contain a certain field.

6. How do you perform sorting on a query?

To perform sorting on a query, you need to use the orderBy() method. This method takes a field name and a direction (ascending or descending) as arguments. For example, to sort a query by the name field in ascending order, you would use the following code:

query.orderBy(“name”, “ascending”);

7. How many documents can be returned from a single call to the Firebase Realtime Database? What’s the limit for Cloud Firestore?

The Firebase Realtime Database can return up to 100 documents from a single call. Cloud Firestore does not have a limit on the number of documents that can be returned from a single call.

8. Are parent-child relationships supported by Cloud Firestore?

Yes, parent-child relationships are supported by Cloud Firestore. You can use Cloud Firestore to create, manage, and query data structures that contain parent-child relationships.

9. What is the difference between Cloud Firestore and Realtime Database?

Cloud Firestore is a newer product from Google that offers several advantages over the older Realtime Database product. Cloud Firestore is a fully managed, cloud-native database that makes it easy to store, sync, and query data for your mobile and web apps. It offers seamless integration with other Firebase and Google Cloud products, and it scales automatically to handle high loads. Realtime Database, on the other hand, is a legacy product that is not as well-suited to modern development needs. It is not as easy to use, it does not scale as well, and it does not offer as many features as Cloud Firestore.

10. Which one do you recommend – Cloud Firestore or Realtime Database? Why?

It depends on the project. If you need a more structured database, then Cloud Firestore is a better choice. If you need a simpler database that can handle more unstructured data, then Realtime Database might be a better choice.

11. What happens when you exceed the document write limit in Cloud Firestore?

When you exceed the document write limit in Cloud Firestore, your app will receive a 429 error code.

12. What does shallow queries mean in the context of Firestore?

A shallow query is a query that only returns the data for a specific document, rather than the data for all of the documents in a collection. This can be useful if you only need to retrieve a small amount of data from a large collection.

13. What is cross-document transactions in Firestore?

Cross-document transactions are a way to update multiple documents in Firestore at the same time. This is useful if you need to make sure that multiple documents are updated in a consistent way, or if you need to update a document based on the contents of another document. Transactions can be used to update documents in different collections, or even in different databases.

14. What types of data can be stored in Cloud Firestore?

Cloud Firestore can store three types of data:

1. Documents: Cloud Firestore stores data in the form of documents, which are organized into collections. Documents can contain any type of data, including sub-collections.

2. Collections: Cloud Firestore stores data in the form of collections, which are similar to tables in a relational database. A collection can contain any number of documents.

3. Sub-collections: Cloud Firestore stores data in the form of sub-collections, which are similar to rows in a relational database. A sub-collection can contain any number of documents.

15. What are the advantages of using Cloud Firestore as compared to other cloud-based NoSQL solutions like DynamoDB?

Cloud Firestore is a newer solution from Google, and it offers several advantages over DynamoDB. First, Cloud Firestore offers automatic scaling, so it can handle more traffic without needing to be manually scaled. Second, Cloud Firestore offers more robust querying capabilities, so you can more easily find the data you need. Finally, Cloud Firestore offers real-time updates, so you can be sure that your data is always up-to-date.

16. What type of security rules can be used with Cloud Firestore?

Cloud Firestore provides a number of different security rules that can be used to control access to data. These rules can be used to allow or deny read and write access to data based on a number of different criteria. For example, rules can be used to allow only authenticated users to access data, or to allow only users with specific roles to access certain data.

17. What should I do if I want to make changes to the structure of my database after deployment?

If you want to make changes to the structure of your database after deployment, you should use the Firebase CLI to export your database to a JSON file. You can then make the changes to the JSON file and import it back into your database.

18. How do you delete a collection in Cloud Firestore?

To delete a collection in Cloud Firestore, you must first delete all of the documents within the collection. Once all documents have been deleted, the collection will be automatically deleted.

19. What is the best way to import large amounts of data into Cloud Firestore?

The best way to import large amounts of data into Cloud Firestore is to use the Cloud Firestore REST API. This will allow you to import data from a JSON file, which can be generated from any data source.

20. What are the limitations of Cloud Firestore?

The biggest limitation of Cloud Firestore is that it is a NoSQL database, which means that it is not as structured as a SQL database. This can make it more difficult to query data, and can also lead to data inconsistencies.