WHAT IS BEFORE UPDATE EVENT IN APEX TRIGGER, EXPLAIN IT WITH AN EXAMPLE?

BEFORE UPDATE:

This event runs the block of code before the updated data is committed to the database. Operations such as validation can be performed under this event to prevent wrong entry in the database.

SYNTAX:

trigger triggerName on objectName (before update) {

   // Block of code

}

SCENARIO:

We are having the requirement to prevent status being updated to “Closed - Converted” status on a lead object when LEAD SOURCE is null. We are going to build a trigger on lead object to prevent status being updated to “Closed - Converted” status when LEAD SOURCE is null.

APEX TRIGGER:

trigger leadMainTrigger on Lead (before update) { // Specifying the event.

    validateLeadData obj=new validateLeadData(); // Declaring the instance of the class.

    if(trigger.isbefore && trigger.isupdate) // Using context variables.

    {

     obj.method1(trigger.new); //Calling apex class method.

    }

}

APEX CLASS:

public class validateLeadData {

    public void method1(List<Lead> leadList){ //Getting list of lead records from trigger.new.

        for(Lead obj:leadList){ //Iterating over lead list.

            if(obj.status=='Closed - Converted' && obj.LeadSource==''){ // checking conditions.

                obj.addError('Lead status can be updated to "Closed - Converted" status only if LEAD SOURCE is not null ');  // Throw error if the conditions are satisfied.

            }  

        } 

    }

}

Now let us update the lead status on record to "Closed - Converted" when LEAD SOURCE is null.