Here is a sample Rollup Summary calculation trigger for Lookup relationship. In below example I’m using Account object as parent and Contact object as child.
I’m updating Account object Account record field Number_of_Contacts__c with Count of all related Contact records.
Apex Trigger:
trigger ContactTrigger on Contact (after insert, after update, after delete, after undelete) {
Set<Id> accountIds = new Set<Id>();
if(trigger.isInsert || trigger.isUpdate || trigger.isUndelete){
for(Contact con:trigger.new){
if(con.AccountId != null){
accountIds.add(con.AccountId);
}
}
}
if(trigger.isUpdate || trigger.isDelete){
for(Contact con:trigger.old){
if(con.AccountId != null){
accountIds.add(con.AccountId);
}
}
}
if(!accountIds.isEmpty()){
List<Account> accList = [SELECT Id, Number_of_Contacts__c, (SELECT Id FROM Contacts)
FROM Account WHERE Id IN : accountIds];
if(!accList.isEmpty()){
List<Account> updateAccList = new List<Account>();
for(Account acc:accList){
Account objAcc = new Account(Id = acc.Id, Number_of_Contacts__c = acc.Contacts.size());
updateAccList.add(objAcc);
}
if(!updateAccList.isEmpty()){
update updateAccList;
}
}
}
}
public with sharing class Sample
{
public string selectedValue {get; set;}
public List<SelectOption> industry {get; set;}
public void getIndustry()
{
Schema.DescribeFieldResult industryDescription = Account.Industry.getDescribe();
industry = new List<SelectOption>();
for (Schema.Picklistentry pl : industryDescription.getPicklistValues())
{
industry.add(new SelectOption(pl.getValue(),pl.getLabel()));
}
}
public void checkValue()
{
System.debug('Selected Industry Type - ' + selectedValue);
}
}