How to clone a list without sharing the reference?

Question

I need a best way to avoid the object reference between two list. For example, I have list of Contact records and I create one more list in which I make the changes to each record's LastName. My problem is, if I make changes in new list, the first list last name also changes. Here is my code.

list<contact> cont = new List<contact>([select id, lastName from contact where lastname Like '%xyz%' Limit 3]);
list<Contact> editedCont = new List<Contact>();
editedCont.addAll(cont);
for(contact c: editedCont)
   c.lastname = 'abc';
System.debug(cont);
System.debug(editedcont);

Answer 1

You don't need to loop at all, this is exactly what List.deepClone() is for.

From the List documentation

deepClone(preserveId, preserveReadonlyTimestamps, preserveAutonumber)

Makes a duplicate copy of a list of sObject records, including the sObject records themselves.

This is in contrast to the regular clone() method, whose documentation says

clone()

Makes a duplicate copy of a list.

Note that if this is a list of sObject records, the duplicate list will only be a shallow copy of the list. That is, the duplicate will have references to each object, but the sObject records themselves will not be duplicated.

To also copy the sObject records, you must use the deepClone method.

Since you do want to make copies of the sObject records themselves, deepClone() is what you'd want to use.

Answer 2

Something like this will get you going.. not sure exactly what you're trying to do

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

for(Contact c: [select id, lastName from contact where lastname Like '%xyz%' Limit 3])
{
    c.lastname = 'abc';
    contactsToUpdate.add(c);

}

update contactsToUpdate;