Getting the records between objects which does not have relation

Question

We already knew that Account and Contact have relationship where as Account is parent. I created one more child for Account called RelateObj. But there is no any relation between RelateObj and Contact.

Now, I want to get Account and Contact records with respect to RelateObj. I tried with this by using Apex collection and it gives this error:

SObject row was retrieved via SOQL without querying the requested field: Contact.Account` and the class is listed below.

public class Example {

    public static List<childtoacc__c> findSiblings() {

    List<Contact> children = [select id,LastName from contact];
    List<RelateObj__c> values = new List<RelateObj__c>();
    Set<Id> parentIds = new Set<Id>();
       for (Contact child : children) {
             parentIds.add(child.Account.Id);
             values = [SELECT Id,name FROM RelateObj__c WHERE Id IN :parentIds];
       }
       System.debug('Values:::'+values);
       return values;
   }
}

Why do I get this error? Can we achieve this functionality only using SOQL?

Answer 1

As the error said, you didn't select the Account.Id field from the list of contacts. But I see an another problem. Your values variable is set in the for loop. Here's the right code:

public class Example {

    public static Map<RelateObj__c, List<Contact>> findSiblings() {

    List<Contact> children = [select id,LastName, Account.Id from contact];
    Map<Id, List<Contact>> contactsByAccountId = new Map<Id, List<Contact>>();
       for (Contact child : children) {
             if(contactsByAccountId.containsKey(child.Account.Id){
                  contactsByAccountId.get(child.Account.Id).add(child);               
             }else{
                  List<Contact> contacts = new List<Contact>(){child};
                  contactsByAccountId.put(child.Account.Id, contacts);
             }
       }

       Map<RelateObj__c, List<Contact>> contactsByRelatedObjs = new Map<RelatedObj__c, List<Contact>>();
       for(RelateObj__c relateObj : [SELECT Id,name, Account__c FROM RelateObj__c WHERE Account__c IN :contactsByAccountId.keySet()){
             contactsByRelatedObjs.put(relateObj, contactsByAccountId.get(relateObj.Account__c));
       }

       return contactsByRelatedObjs;
   }
}