Master to detail referencing in query

Question

I have below piece of code where I want to traverse to details from the base query on master object. But I am getting error Like :

Error

Compile Error: Didn't understand relationship 'Account_List_Item_vod__r' in FROM part of query call. If you are attempting to use a custom relationship, be sure to append the '__r' after the custom relationship name. Please reference your WSDL or the describe call for the appropriate names

Apex code

Map<Id,set<Id>> MapOfAcctListItem = new Map<Id,Set<Id>>();

              for(Account_List_vod__c cpc : [select Access_vod__c,Display_Order_vod__c,Icon_Name_vod__c,Id,Name,OwnerId, 
                                                        (select ID,Account_vod__c,External_ID_vod__c 
                                                         from Account_List_Item_vod__r) 
                                                 from Account_List_vod__c 
                                                 where OwnerId in :MapOfTierObj.keyset()
                                                 And Name =:ListName])
        {
            if(!cpc.Account_List_Item_vod__r.isempty())
            {
                if(!MapOfAcctListItem.containsKey(cpc.OwnerId)){
                    MapOfAcctListItem.put(cpc.OwnerId,cpc.Account_List_Item_vod__r);}
                else{    
                MapOfAcctListItem.get(cpc.OwnerId).addAll(cpc.Account_List_Item_vod__r);}
            }
        }

Can someone please let me know where I go wrong here?

Answer 1

You can get the specific API Name of the child relationship using describes. Run this script via Execute Anonymous, substituting the proper names for parent and child objects:

for (ChildRelationship relation : SObjectType.Parent__c.getChildRelationships())
    if (relation.getChildSobject() == Child__c.sObjectType)
        system.debug(relation.getRelationshipName());

In this case you would change Parent__c to Account_List_vod__c and change Child__c to Account_List_Item_vod__c, though I'm making a guess at the name of the child object.