What happens when a contact changes the identifier

Question

Let's imagine we were using a sitecore username as an identifier (example), but later we realized that it is better to use an email as an identifier.

So, we started identifying our visitors using their email rather then username.

However, what happens to the old data? Will it be automatically merged or there will be two distinct contacts?

Also what are the general implications of changing the contact identifier?

Answer 1

When using the Identify() method and switching identifiers, because the contact is known, Identify() won't merge the contacts like it would for an anonymous original contact.

So the end result is that you will have two contacts in xDB, one for each identifier. The information isn't lost, but it's not tracked as one contact.

That's where ContactManager would come into play.

There is a public method on ContactManager called MergeContacts.

public void MergeContacts(Contact survivingContact, Contact dyingContact)
{
  Sitecore.Diagnostics.Assert.IsFalse(survivingContact.IsReadOnly, "Cannot save a read-only contact to XDB.");
  Sitecore.Diagnostics.Assert.IsFalse(dyingContact.IsReadOnly, "Cannot save a read-only contact to XDB.");
  if (this.repository == null)
    return;
  this.repository.MergeContacts(survivingContact, dyingContact);
}

I would use this method, and maybe a script (see Dmytro's link in comment for approaches) and use this method to merge the contacts, and "kill" off the Dying Contact, and "keep" the Surviving Contact