Trigger on child object to update parent field

Question

I am trying to update a Custom check-box field 'IsDepartment__c' in Parent Object 'Contact' that when child object/s 'DepartmentOfContact__c' is/are created or undeleted then that field will be checked and when deleted will be unchecked. but it is not working properly

public with sharing class DepartmentOfContactExistHandler {
private List<DepartmentOfContact__C> newList;
private List<DepartmentOfContact__C> oldList;
private Map<Id, DepartmentOfContact__C> oldMap;
private Map<Id, DepartmentOfContact__C> newMap;

public DepartmentOfContactExistHandler( List<DepartmentOfContact__C> newList, List<DepartmentOfContact__C> oldList, Map<Id, DepartmentOfContact__C> oldMap, Map<Id, DepartmentOfContact__C> newMap ){
    this.newList = newList;
    this.oldList = oldList;
    this.newMap = newMap;
    this.oldMap = oldMap;
}
public void ifDepartmentExistforContact(){
    set<Id> conIds = new set<Id>();

    for(DepartmentOfContact__C dep: newList){
        conIds.add(dep.Contact__r.Id);
    }
    Map<ID, DepartmentOfContact__C> depofConfoContacts = new Map<ID, DepartmentOfContact__C>([select Id from DepartmentOfContact__C where Contact__r.Id IN :conIds]);
    Map<ID, Contact> consToUpdate = new Map<ID, Contact>([select Id,IsDepartment__c,(select Id from DepartmentOfContact__r) from Contact where Id IN :conIds]);
    for(Contact con : consToUpdate.values()){
        Set<ID> depofConIds = new Set<ID>();
        for (DepartmentOfContact__C depcon : depofConfoContacts.values()) {
            if (depcon.Contact__r.Id == con.Id)
                depofConIds.add(depcon.Contact__r.Id);
        }
        if (con.IsDepartment__c != false && depofConIds.size()== null){
            con.IsDepartment__c = false;
        }else if(con.IsDepartment__c == false && depofConIds.size()!= null){
            con.IsDepartment__c = true;
        }   
    }
    if(consToUpdate.values()!= null){
        update consToUpdate.values();
    }
}
public void ifDepartmentdelforContact(){
    set<Id> conIds = new set<Id>();

    for(DepartmentOfContact__C dep: oldList){
        conIds.add(dep.Contact__r.Id);
    }
    Map<ID, DepartmentOfContact__C> depofConfoContacts = new Map<ID, DepartmentOfContact__C>([select Id from DepartmentOfContact__C where Contact__r.Id IN :conIds]);
    Map<ID, Contact> consToUpdate = new Map<ID, Contact>([select Id,IsDepartment__c from Contact where Id IN :conIds]);
    for(Contact con : consToUpdate.values()){
        Set<ID> depofConIds = new Set<ID>();
        for (DepartmentOfContact__C depcon : depofConfoContacts.values()) {
            if (depcon.Contact__r.Id == con.Id)
                depofConIds.add(depcon.Contact__r.Id);
        }
        if (con.IsDepartment__c != false && depofConIds.size()== null){
            con.IsDepartment__c = false;
        }else if(con.IsDepartment__c == false && depofConIds.size()!= null){
            con.IsDepartment__c = true;
        }

    }
    if(consToUpdate.values()!= null){
        update consToUpdate.values();
    }
  }

}

and my trigger is on child object

trigger DepertmentOfContact on DepartmentOfContact__c (after delete, after insert, after undelete, 
after update) {

    if(Trigger.isAfter && Trigger.isInsert){
        DepartmentOfContactExistHandler dep1 = new DepartmentOfContactExistHandler(Trigger.new, Trigger.old, Trigger.oldMap, Trigger.newMap);
        dep1.ifDepartmentExistforContact();

    }


    if(Trigger.isAfter && Trigger.isUpdate){

        DepartmentOfContactExistHandler dep2 = new DepartmentOfContactExistHandler(Trigger.new, Trigger.old, Trigger.oldMap, Trigger.newMap);
        dep2.ifDepartmentExistforContact();
    }

    if(Trigger.isAfter && Trigger.isDelete){

        DepartmentOfContactExistHandler dep3 = new DepartmentOfContactExistHandler(Trigger.new, Trigger.old, Trigger.oldMap, Trigger.newMap);
        dep3.ifDepartmentdelforContact();

    }
    if(Trigger.isAfter && Trigger.isUndelete){

        DepartmentOfContactExistHandler dep4 = new DepartmentOfContactExistHandler(Trigger.new, Trigger.old, Trigger.oldMap, Trigger.newMap);
        dep4.ifDepartmentExistforContact();

       }

    }

Answer 1

If you have made the relationship a master-detail one (or can change it to one), you could accomplish this by adding a roll-up summary field to Contact that counts the number of DepartmentOfContact__c objects and then have a second checkbox formula field based off that that checks whether the count is greater than zero. There is a maximum of 10 of these roll-up summary fields per object at present.

One problem in your trigger code is that you are referencing relationship fields that are not populated in triggers. So instead of dep.Contact__r.Id use dep.Contact__c.

If you want to stick to the trigger approach, then something like this should work. It does less queries and doesn't contain doubly nested loops that become a performance problem when large numbers of objects are involved:

trigger DepartmentOfContact on DepartmentOfContact__c (after delete, after insert,
        after undelete, after update) {

    Set<Id> falseIds = new Set<Id>();
    Set<Id> trueIds = new Set<Id>();
    if (Trigger.isDelete || Trigger.isUpdate) {
        for (DepartmentOfContact__c d : Trigger.old) {
            if (d.Contact__c != null) falseIds.add(d.Contact__c);
        }
    }
    if (Trigger.isInsert || Trigger.isUndelete || Trigger.isUpdate) {
        for (DepartmentOfContact__c d : Trigger.new) {
            if (d.Contact__c != null) trueIds.add(d.Contact__c);
        }
    }
    if (falseIds.size() > 0 || trueIds.size() > 0) {
        // Query for Contacts that are in the wrong state and update them
        Contact[] contacts = [
                select Id
                from Contact
                where (Id in :falseIds and IsDepartment__c = true)
                or (Id in :trueIds and IsDepartment__c = false)
                ];
        for (Contact c : contacts) {
            c.IsDepartment__c = !falseIds.contains(c.Id);
        }
        update contacts;
    }
}

The Trigger.isUpdate is the awkward case when the Contact__c changes because the old and new Contact need updating. Code could be added to check that it is that specific field that is changing.