Platform Events in Lightning (Emp API)

We can use Platform Events in Lightning (Emp API) to connect business processes in Salesforce and external sources through the exchange of real-time event data.  Platform events are secure and scalable. We can create a Platform Event and add custom fields as per the business needs. Platform event messages are published to the Event Bus. Messages are stored in Event Bus temporarily which can be retrieved by components that subscribe to these events. Let’s get into the implementation.

Implementation

In this implementation, we will create a Rest Resource that will create a Case and publish a Platform Event. External Application will call this web service. Lightning Component in Utility Bar will subscribe to this event and open a Case automatically in Salesforce.

Create Connected App

Create a Connected App and enable OAuth Settings. Check this post to know how to create and set up a Connected App. Consumer Key and Secret will be generated. Connected App should look something like below:

Create Platform Event

Platform Events and fields are created in the same way we create Objects and fields.

• Type Platform Event in Quick Find box and click on Platform Events under Integrations.
• Click on the New Platform Event and provide Label and Plural Label. For Publish Behaviour, select Publish After Commit to publish the event only after the transaction is successful. Click Save.
• Under Custom Fields & Relationships, click New and add CaseId field of type Text.

Publish Platform Event from REST Resource

We can publish the event messages from a Salesforce app using Processes, Flows, Apex, or an External App using Salesforce APIs. In the implementation, we will publish from Apex Rest Resource.

To publish an event message from Apex Class, we just need to create an instance of Platform Event we created earlier. Add it in the list and use EventBus.publish() to publish the event messages.

Below is the simple Rest Resource that accepts the subject and description from the HTTP Request and creates a Case. It also publishes the Platform event with the Id of the Case.

CaseResource.apxc

@RestResource(urlMapping='/CaseService/')
global class CaseResource {
	
    @HttpPost
    global static String createCase(String subject, String description){
        Case objCase = new Case(Subject = subject, Description = description, 
                                AccountId = [SELECT Id FROM Account WHERE Name = 'Niks Developer' LIMIT 1].Id);
        insert objCase;
        
        // Creating a Platform event.
        list<New_Case__e> newCaseList = new list<New_Case__e>{new New_Case__e(CaseId__c = objCase.Id)};
            
        // Calling method to publish events
        List<Database.SaveResult> newCaseResults = EventBus.publish(newCaseList);
        
        // Error Handling
        for (Database.SaveResult sr : newCaseResults) {
            if (sr.isSuccess()) {
                System.debug('Successfully published event.');
            } else {
                for(Database.Error err : sr.getErrors()) {
                    System.debug('Error returned: ' +err.getStatusCode() +' - ' +err.getMessage());
                }
            }       
        }
        return objCase.Id;
    }
}

Subscribe to Platform Event

We can subscribe and receive event messages in Processes, Flows, Apex triggers, or CometD clients. In this implementation, we will subscribe from Lightning Aura Component.

First, we need to add lightning:empApi utility in the component. In doInit handler of JS Controller, we have to call a subscribe method of empApi utility and pass the channel and replayId. Channel contains the name of Event and replayId is used to get the new events. There is more to replayId but we will cover that later. For now, just assign -1 to it. Add the logic to open a new case from the Case Id retrieved from event.data.payload. Then() is used to perform post subscription logic like saving the subscriptions to unsubscribe it later.

We have to keep this component in Utility Bar. Because it should stay subscribed to Platform Event all the time so that every time a Case is created by External Application, it should open in Salesforce application. Only Utility Bar is available on all the pages in the Salesforce application.

subscribeCmp.cmp

<aura:component implements="flexipage:availableForAllPageTypes, lightning:utilityItem" access="global" >
	<lightning:empApi aura:id="empApi"/>
    
     <!-- Calls the onInit controller function on component initalization -->
    <aura:handler name="init" value="{!this}" action="{!c.doInit}"/>
    
    <!-- Holds the streaming event subscription -->
    <aura:attribute name="subscription" type="Map" />

    <!-- Form for subscribing/unsubscribing to/from events -->
    <lightning:input aura:id="channel" label="channel" name="channel" type="text" value="/event/New_Case__e"/>
</aura:component>

subscribeCmpController.js

({
	doInit : function(component, event, helper) {
        
		// Get the empApi component
        const empApi = component.find('empApi');
        // Get the channel from the input box
        const channel = '/event/New_Case__e';
        // Replay option to get new events
        const replayId = -1;

        // Subscribe to an event
        empApi.subscribe(channel, replayId, $A.getCallback(eventReceived => {
            var casePayload = eventReceived.data.payload;
            
            // Process event
            var navEvt = $A.get("e.force:navigateToSObject");
            navEvt.setParams({
              "recordId": casePayload.CaseId__c
            });
    		navEvt.fire();
        }))
        .then(subscription => {
    		// Post Subscription Logic.
            console.log('Subscription request sent to: ', subscription.channel);
            // Save subscription to unsubscribe later
            component.set('v.subscription', subscription);
        });
	}
})

Go to App Manager from Quick Find box. Edit the App, Click on Utility Items in the sidebar. Click on Add Utility Item and select our component. For Panel Width and Panel Height, enter 1 and click on Start automatically checkbox. Click Save. It will add the component in Utility Bar but it will not popup after clicking as the width and height are 1. Still, It will still execute all the code written inside. That is all we needed to run our implementation. Let’s test it.

Platform Events in Lightning (Emp API)

To test this, we just need to call our Web Service and pass the subject and description. We will test this using Username and Password flow from Postman.

• First hit the Token URL with username, password, client_id, client_secret, and grant_type (password) as query parameters with the POST method. Make sure to append the Security token to password.
• We will get the access_token. Use this access_token to call our Web Service with Authorization and Content-Type header. Pass the subject and description in the request body.

Note: & in below Endpoints might be replaced with &

Token Endpoint:

https://<your domain>/services/oauth2/token?username=<username>&password=<password+securitytoken>&grant_type=password&client_id=<clientid from connected app>&client_secret=<clientsecret from connected app>

Web Service Endpoint:

https://<your domain>/services/apexrest/CaseService/

If you get an authentication failure error, just add your user’s profile in the Connected App.

This is how we can use Platform Events in Lightning (Emp API). Check official Salesforce documentation here to know more about Platform Events. If you like this implementation, you may want to check the following hand-picked implementations for you.

• Lightning Message Service – Future of Communication
• Publish-Subscribe Model in LWC
• Named Credentials in Salesforce with Example
• Named Credentials using OAuth 2.0
• Named Credentials PER USER with OAuth 2.0

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