Building a Mobile Chat App Using Realm – Integrating Realm into Your App
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If you're looking to add a chat feature to your mobile app, you can repurpose the article's code and the associated repo. If not, treat it as a case study that explains the reasoning behind the data model and partitioning/syncing decisions taken. You'll likely need to make similar design choices in your apps.
Update: March 2021
If you want to build and run the app for yourself, this is what you'll need:
Name the app "RChat" and click "Create Realm Application":
Copy the "App ID." You'll need to use this in your iOS app code:
Let's start by looking at some of the
When logged in, the app opens two realms:
userRealmlets the user read and write just their own data from the Atlas
chatsterRealmenables the user to read data for every user from the Atlas
The app uses the to interact with the back end Realm application to perform actions such as logging into Realm. Those operations can take some time as they involve accessing resources over the internet, and so we don't want the app to sit busy-waiting for a response. Instead, we use publishers and subscribers to handle these events.
userRealmPublisherare publishers to handle logging in, logging out, and opening realms for a user:
AppStateclass is instantiated, the realms are initialized to
niland actions are assigned to each of the Combine publishers:
We'll later see that an event is sent to
chatsterLoginPublisherwhen a user has successfully logged into Realm. In
AppState, we define what should be done when those events are received. For example, events received on
loginPublishertrigger the opening of a realm with the partition set to
user=<id of the user>, which in turn sends an event to
When the realm has been opened and the realm sent to
userRealmPublisher, the Realm struct is stored in the
userRealmattribute and the local
useris initialized with the
Userobject retrieved from the realm:
chatsterLoginPublisherbehaves in the same way, but for a realm that stores
After logging out of Realm, we simply set the attributes to nil:
After seeing what happens after a user has logged into Realm, we need to circle back and enable email/password authentication in the back end Realm app. Fortunately, it's straightforward to do.
From the Realm UI, select "Authentication" from the lefthand menu, followed by "Authentication Providers." Click the "Edit" button for "Email/Password":
Enable the provider and select "Automatically confirm users" and "Run a password reset function." Select "New function" and save without making any edits:
Don't forget to click on "REVIEW & DEPLOY" whenever you've made a change to the back end Realm app.
Select "Triggers" and then click on "Add a Trigger":
Set the "Trigger Type" to "Authentication," provide a name, set the "Action Type" to "Create" (user registration), set the "Event Type" to "Function," and then select "New Function":
Name the function
createNewUserDocumentand add the code for the function:
Note that we set the
user=<id of the user>, which matches the partition used when the iOS app opens the User realm.
"Save" then "REVIEW & DEPLOY."
Browse to the "Rules" section in the Realm UI and click on "Add Collection." Set "Database Name" to
RChatand "Collection Name" to
User. We won't be accessing the
Usercollection directly through Realm, so don't select a "Permissions Template." Click "Add Collection":
At this point, I'll stop reminding you to click "REVIEW & DEPLOY!"
Select "Schema," paste in this schema, and then click "SAVE":
Repeat for the
And for the
Realm Sync is used to synchronize objects between instances of the iOS app (and we'll extend this app to also include Android). It also syncs those objects with Atlas collections. Note that there are three options to create a Realm schema:
- Manually code the schema as a JSON schema document.
- Derive the schema from existing data stored in Atlas. (We don't yet have any data and so this isn't an option here.)
- Derive the schema from the Realm objects used in the mobile app.
We've already specified the schema and so will stick to the first option.
Select "Sync" and then select your Atlas cluster. Set the "Partition Key" to the
partitionattribute (it appears in the list as it's already in the schema for all three collections), and the rules for whether a user can sync with a given partition:
The "Read" rule controls whether a user can establish one-way read-only sync relationship to the mobile app for a given user and partition. In this case, the rule delegates this to a Realm function named
The "Write" rule delegates to the
To create these functions, select "Functions" and click "Create New Function." Make sure you type the function name precisely, set "Authentication" to "System," and turn on the "Private" switch (which means it can't be called directly from external services such as our mobile app):
Create a Realm function named
userDocWrittenTo, set "Authentication" to "System," and make it private. This article is aiming to focus on the iOS app more than the back end Realm app, and so we won't delve into this code:
Set up a database trigger to execute the new function whenever anything in the
We've now created enough of the back end Realm app that mobile apps can now register new Realm users and use them to log into the app.
When first run, no user is logged in and so
AppState.loggedInchecks whether a user is currently logged into the Realm
Clicking the button executes one of two functions:
signupmakes an asynchronous call to the Realm SDK to register the new user. Through a Combine pipeline,
signupreceives an event when the registration completes, which triggers it to invoke the
loginfunction uses the Realm SDK to log in the user asynchronously. If/when the Realm login succeeds, the Combine pipeline sends the Realm user to the
loginPublisherpublishers (recall that we've seen how those are handled within the
When the view loads, the UI is populated with any existing profile information found in the
Userobject in the
As the user updates the UI elements, the Realm
Userobject isn't changed. It's only when they click "Save User Profile" that we update the
Userobject. Note that it uses the
userRealmthat was initialized when the user logged in to open a Realm write transaction before making the change:
Once saved to the local realm, Realm Sync copies changes made to the
Userobject to the associated
Userdocument in Atlas.
Once the user has logged in and set up their profile information, they're presented with the
At any time, another user can include you in a new group conversation. This view needs to reflect those changes as they happen:
When the other user adds us to a conversation, our
Userdocument is updated automatically through the magic of Realm Sync and our Realm trigger; but we need to give SwiftUI a nudge to refresh the current view. We do that by registering for Realm notifications and updating the
lastSyncstate variable on each change. We register for notifications when the view appears and deregister when it disappears:
When the status of a conversation changes (users go online/offline or new messages are received), the card displaying the conversation details should update.
conversation.unreadCountis part of the
Userobject and so we need another Realm trigger to update that whenever a new chat message is posted to a conversation.
We add a new Realm function
chatMessageChangethat's configured as private and with "System" authentication (just like our other functions). This is the function code that will increment the
Userdocuments for members of the conversation:
That function should be invoked by a new Realm database trigger (
ChatMessageChange) to fire whenever a document is inserted into the
Note that we only open a
Conversationrealm when the user opens the associated view because having too many realms open concurrently can exhaust resources. It's also important that we stop observing the realm by setting it to
nilwhen leaving the view:
To send a message, all the app needs to do is to add the new chat message to Realm. Realm Sync will then copy it to Atlas, where it is then synced to the other users:
In this article, we've gone through the key steps you need to take when building a mobile app using Realm, including:
- Managing the user lifecycle: registering, authenticating, logging in, and logging out.
- Managing and storing user profile information.
- Adding objects to Realm.
- Performing searches on Realm data.
- Syncing data between your mobile apps and with MongoDB Atlas.
- Reacting to data changes synced from other devices.
- Adding some back end magic using Realm triggers and functions.
There's a lot of code and functionality that hasn't been covered in this article, and so it's worth looking through the rest of the app to see how to use features such as these from a SwiftUI iOS app:
- Location data
- Camera and photo library
- Actions when minimizing your app
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