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Writing your first apex trigger

Triggers are written to respond to the database changes and execute a set of business rule when these changes occur. Before we write a trigger let's understand the trigger and trigger handler class.

Trigger

Trigger is a piece of code written to act on database changes on a particular object. You should write only one trigger as an entry point the database changes for an object. If you write multiple triggers, your business calculations may not work as expected because the order of execution of a trigger is not guranteed in salesforce.

Trigger handler

A trigger handler is an apex class where the main logic for a trigger is written. The trigger itself should not contain any business logic. You can have one or more trigger handlers for an object in salesforce.

Trigger should only capture database events and then pass control to the trigger handler class to handle the business logic.

Trigger

Trigger Handler 1

Trigger Handler 2

Following is an example of an account trigger that sets the account industry to 'Technology' if the industry is blank:

In the above example:

Trigger

The file AccountTrigger is a trigger written on Account object, which will be invoked before a new record is inserted (Before Insert event) into the database.
The apex class AccountTriggerHandler is implementing the business logic for the AccountTrigger, which is called from the trigger.
The trigger context variables Trigger.isInsert, Trigger.isBefore, is used to conditionally invoking the handleBeforeInsert method from apex trigger. This is to make sure that trigger handler runs only for the Before Insert event.

Trigger Handler

The apex class AccountTriggerHandler is the trigger handler.
The Trigger.new method is used to get all the records in the trigger context in the trigger handler.
The Trigger.new returns a list of Sobjects, which is conveted to a list of account records using typcasting in apex.
The for loop for collection is used to iterate through all records and set the Industry to 'Technology' if it is blank.

Note

Always use a list to operate on the records that invoke the trigger, this is called bulkification. The trigger can be invoked from a single record or a list of records (up to 200). Bulkification helps to reduce system resource usage and avoid hitting governor limit exceptions.

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