Update Number of Contact on Account

Write a trigger to update the number of related contact of the given account.

trigger contrigger on Contact (after update, after insert, after delete) {

    List<Contact> conlist = new List<Contact>();

    Set<id> accIdSet = new set<id>();

   

    if(trigger.isUpdate || trigger.isInsert)

        conlist = trigger.new;

    if(trigger.isDelete)

        conlist = trigger.old;

   

    for(contact c : conlist){

        if(c.AccountId != null)

                accIdSet.add(c.AccountId);

    }

   

    List<Account> acclist = new List<Account>();

    for(account acc : [Select Id,Number_Of_Contact__c, (select id from Contacts ) from account where id in :accIdSet ]){

        acc.Number_Of_Contact__c= acc.contacts.size();

        acclist.add(acc);

    }

    Database.update(acclist);

}