Method does not exist or incorrect signature: void containsKey(Id) from the type Set<Id>

Question

I am getting the following error on line 12 and 25 and would need some help in resolving it.

Error on line 12:

Method does not exist or incorrect signature: void containsKey(Id) from the type Set

Error on Line 25:

Method does not exist or incorrect signature: void get(Id) from the type List

trigger UpdateContactPhoneNumberOnCases on Contact (after update) {
List <case> affectedCases = [select id, Contact_Phone__c  from case 
                            where contactId in : trigger.newMap.keyset()];

    // A map of contact Ids -> to list of cases

    map<id, list<case>> affectedCasesByContactId = new Map<Id,List<case>>();

    // Now populate the map  (affectedCasesByContactId)

    for (case c: affectedCases) {
**12---->**        if (affectedCasesByContactId.keyset().containsKey(c.contactId)){
            affectedCasesByContactId.get(c.contactId).add(c);

        }else {
            affectedCasesByContactId.put(c.contactId, new List<case>{c});
        }

    }

// create a new list to hold our newly updated cases

    List <case> updatedcases = new List<case>();
    for (Id contactId: trigger.newMap.keyset()) {        
**25--->** if(trigger.old.get(contactId).phone != trigger.new.get(contactId).phone)
           {
            for (case thisCase: affectedCasesByContactId.get(contactId)){
            thisCase.Contact_Phone__c = trigger.new.get(contactId).phone;
            updatedcases.add(thisCase);
        }
    }

}
           try{
           update updatedcases;
           } catch (exception e){
               system.debug(e.getMessage());
           }
           }

Answer 1

For the first one, instead of:

affectedCasesByContactId.keyset().containsKey(...)

use either the Map method containsKey on the Map:

affectedCasesByContactId.containsKey(...)

or the Set method contains on the Set:

affectedCasesByContactId.keyset().contains(...)

For the second one instead of trying to access from the List:

trigger.new.get(...)

access from the Map:

trigger.newMap.get(...)

Take a look at the available Trigger Context Variables and also do some Googling about lists and maps to get clear about how to use those most effectively.

Answer 2

The method you're looking for is contains(). containsKey() is in Map, not Set.