I don't know the rest logic how to add both contacts amount and display it account

Question

if a contact has a custom field as amount and account have a custom field total amount roll up the amount field on account if one account associated have two contacts. 1)first contact amount is 20 2)second contact amount is 30 then total amount will display 50 in account

Below is my code. I display contact amount field in account total amount I don't know how to do the rest of the logic. how can i add both contacts amount and display it in account

trigger CopyPhoneOnContact on Contact (before insert) {

List<String> upcon =new List<String>();
List<account> up=new List<account>();

for(contact c:trigger.new)
{
    upcon.add(c.accountid);
}
List<account> acc=[select phone from account where id in:upcon];

for(account a:acc)
{
    for(contact c:trigger.new)
    {
        if((a.id).equals(c.AccountId))
        {
            a.phone=c.Phone;
            up.add(a);
        }
    }
}
update up;

}

Answer 1

I think your issue is that you are trying to do this on the wrong trigger. It will be a lot easier to keep track of which contacts are part of which account if you do the logic in the Account trigger instead:

trigger updateRollUp on Account(before update)
{
    Map<ID, List<Contact>> contacts = new Map<ID, List<Contact>>();
    for(Account accn : trigger.new)
    {
        contacts.put(accn.ID, new List<Contact>();
    }
    for(Contact cont : [select Amount__c from Contact where accountid in :trigger.new])
    {
        contacts.get(cont.accountid).add(cont);
    }
    for(Account accn : trigger.new)
    {
        if(contacts.get(accn.ID).size() > 1)
        {
            accn.Total_Amount__c = 0;
            for(Contact cont : contacts.get(accn.ID))
            {
                accn.Total_Amount__c += cont.Amount__c;
            }
        }
    }
}

Your existing code just needs to only have one copy of each Account in your DML, but that's a relatively simple change, just call update on acc instead of up. Note that you can run into a recursion issue if your account trigger updates child contacts - how exactly this should be handled depends on your business rules, but it can be managed by using static variables, which persist through the whole database transaction.