Getting Started With Cloud Firestore for iOS

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Mobile coders have been taking advantage of Google’s Mobile Backend as a Service (MBaaS) platform Firebase Realtime Database for many years, helping them focus on building features for their apps without having to worry about the back-end infrastructure and database. By making it easy to store and persist data in the cloud and take care of authentication and security, Firebase allows coders to focus on the client side. 

Last year, Google announced yet another back-end database solution, Cloud Firestore, built from the ground up with the promise of greater scalability and intuitiveness. However, this introduced some confusion as to its place in relation to Google’s already existing flagship product, Firebase Realtime Database. This tutorial will outline the differences between the two platforms and the distinct advantages of each. You will learn how to work with Firestore document references, as well as reading, writing, updating and deleting data in real time, by building a simple reminders app.

Objectives of This Tutorial

This tutorial will expose you to Cloud Firestore. You'll learn how to leverage the platform for real-time database persistence and synchronization. We'll cover the following topics:

  • what Cloud Firestore is
  • the Firestore data model
  • setting up Cloud Firestore
  • creating and working with Cloud Firestore references
  • reading data in real time from Cloud Firestore
  • creating, updating and deleting data
  • filtering and compound queries

What Is Cloud Firestore?

Like Firebase Realtime Database, Firestore provides mobile and web developers with a cross-platform cloud solution to persist data in real time, regardless of network latency or internet connectivity, as well as seamless integration with the Google Cloud Platform suite of products. Along with these similarities, there are distinct advantages and disadvantages that differentiate one from the other. 

Data Model

On a fundamental level, Realtime Database stores data as one large, monolithic, hierarchical JSON tree, whereas Firestore organizes data in documents and collections, as well as sub-collections. This requires less denormalization. Storing data in one JSON tree has the benefits of simplicity when it comes to working with simple data requirements; however, it becomes more cumbersome at scale when working with more complex hierarchical data. 

Offline Support

Both products offer offline support, actively caching data in queues when there is latent or no network connectivity—synchronising local changes back to the back end when possible. Firestore supports offline synchronisation for web apps in addition to mobile apps, whereas the Realtime Database only enables mobile synchronization.

Queries and Transactions 

Realtime Database only supports limited sorting and filtering capabilities—you can only sort or filter on a property level, but not both, in a single query. Queries are also deep, meaning they return a large sub-tree of results back. The product only supports simple write and transaction operations which require a completion callback. 

Firestore, on the other hand, introduces index queries with compound sorting and filtering, allowing you to combine actions to create chain filters and sorting. You can also execute shallow queries returning sub-collections in lieu of the entire collection you would get with Realtime Database. Transactions are atomic in nature, whether you send a batch operation or single, with transactions repeating automatically until concluded. Additionally, Realtime Database only supports individual write transactions, whereas Firestore affords batch operations atomically.

Performance and Scalability

The Realtime Database, as you would expect, is quite robust and has low latency. However, databases are restricted to single regions, subject to zonal availability. Firestore, on the other hand, houses data horizontally across multiple zones and regions to ensure true global availability, scalability, and reliability. In fact, Google has promised that Firestore will be more reliable than Realtime Database. 

Another shortcoming of the Realtime Database is the limitation to 100,000 concurrent users (100,000 concurrent connections and 1,000 writes/second in a single database) after which you would have to shard your database (split your database into multiple databases) in order to support more users. Firestore automatically scales across multiple instances without you having to intervene. 

Designed from the ground up with scalability in mind, Firestore has a new schematic architecture that replicates data across multiple regions, takes care of authentication, and handles other security-related matters all within its client-side SDK. Its new data model is more intuitive than Firebase's, more closely resembling other comparable NoSQL database solutions like MongoDB, while providing a more robust querying engine. 


Finally, Realtime Database, as you know from our previous tutorials, manages security through cascading rules with separate validation triggers. This works with Firebase Database Rules, validating your data separately. Firestore, on the other hand, provides a simpler yet more powerful security model taking advantage of Cloud Firestore Security Rules and Identity and Access Management (IAM), with data validation excepted automatically.


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