How to get PermissionSet oldMap value and compare with new one in after update trigger

Question

I need to figure out if values in PermissionSet for current user are changed in trigger, i'm thinking about using oldMap but i can't figure it out.

Maybe this code will explain what i'm trying to do:

    for (User u : trigger.New)
    {
        List<PermissionSetAssignment> lstOldPermSet = Trigger.oldMap.get(u.id).PermissionSetAssignments;
        List<PermissionSetAssignment> lstNewPermSet = // get PermissionSetAssignments via soql query

        if(lstOldPermSet != lstNewPermSet)
        {

// code goes in here

        }

    }

Any suggestions?

Answer 1

The after update trigger on User object will fire only when you will update any field of the User object.

If you will add or remove thePermissionSets, the trigger on User object will not fire.