Platform Event

 What is Platform Event?

• Platform Event is based on Event-Driven Architecture enable apps to communicate inside and outside of Salesforce.
• Platform events are based on the publish/subscribe model and work directly with a message bus that handles the queue of incoming events and processes listening for them. This is built-in real-time integration patterns in the Salesforce Platform which help to reduce point-to-point integration

What is Event-Driven Software Architecture?

An event-driven (or message-driven) software architecture consists of event producers, event consumers, and channels.

• Event: A change in state that is meaningful in a business process.
• Event message / Notification: A message that contains data about the event.
• Event producer: The publisher of an event message over a channel.
• Channel: A conduit in which an event producer transmits a message. Event consumers subscribe to the channel to receive messages. Also referred to as event bus in Salesforce.
• Event consumer: A subscriber to a channel that receives messages from the channel

Characteristics of Platform Event

•  SObject like Salesforce Entity
• Suffixed with __e
•  Only Checkbox, Date, Date/Time, Number, Text, and Text Area field available.
• Pub / Sub based communication
• No Polling required. Whenever an event occurs, the consumer will get notified  

Difference between SObject and Platform Events-

• Platform event only support insert whereas sObject support all DML
• You can not query Platform events through SOQL or SOSL
• You can not use Platform in reports, list views, and search. Platform events don’t have an associated tab
• Published platform events can’t be rolled back.
• Only after insert Triggers Are Supported

Publishing / Subscribing Platform Events-

Publish Platform Events

We can publish platform events in 3 ways:

1. Publish Events Messaging using APEX- User EventBus.publish() method to publish
2. Publish Events Messaging using Declarative tools 
3. Publish Events Messaging using Salesforce API from external app

Subscribing Platform Events :

We can subscribe to the platform events with the following ways :

1. Apex Trigger-Write an “after insert” Apex trigger on the event object to subscribe to incoming events.
2. Subscribe to platform event notification in Lightning components
1. Lightning web components :  Use the empApi methods in your Lightning web component, import the methods from the lightning/empApi module as follows
   
   
   import { subscribe, unsubscribe, onError, setDebugFlag, isEmpEnabled }
       from 'lightning/empApi';
2. Subscibe in an Aura Component : Use the empApi methods in your Aura component, add the lightning:empApi component inside your custom component and assign an aura:id attribute to it
   
   <lightning:empApi aura:id="empApi"/>
3. In an external app, you subscribe to events using CometD as well.
4. Flow and process builder. Check this post.

To know about other integration API at a glance, pls Click here