How do I update a grandchild's field if there is a change in grandparent field? I know I have to write a trigger because its cross object

I can access the immediate child record of parent which is child

 List<parent__c> fbr = [SELECT Name , 
                           (SELECT Id , Name, CreatedDate FROM child__r) 
                           FROM parent__c];

Any reference will be helpful. Thanks

Attribution to: MnZ

Possible Suggestion/Solution #1

"In each specified relationship, only one level of parent-to-child relationship can be specified in a query. For example, if the FROM clause specifies Account, the SELECT clause can only specify the Contact or other objects at that level. It could not specify a child object of Contact." (http://www.salesforce.com/us/developer/docs/dbcom_soql_sosl/Content/sforce_api_calls_soql_relationships.htm)

One option would be to rephrase the query, if you can, into a select from the Grandchild object, as you can reference 5 levels of parents upwards. e.g.

select child__r.parent__r.name, name from grandchild__c where ....

Attribution to: Doug B

Possible Suggestion/Solution #2

You can get your grandchilderen with a subselect in the SOQL where clause.

In words:

Select the grandchilderend who's parent's parent is one of the grandparents you have.

In code:

//example=  account (parent) -> testobject__c -> testChildObject__c (grandchild)

    List<Account> accs = trigger.New;  //list of grandparents that have been changed
    list<testChildObject__c> lst = [SELECT Id,name, testobject__c 
                                    FROM testChildObject__c 
                                    WHERE testObject__c In (SELECT id 
                                                            FROM testObject__C 
                                                            WHERE Account_lookup__c in:accs
                                                            )
                                  ];

• testChildObject__c object has a lookup to the testobject__c: field testObject__c
• testobject__c object has a looup to account: field Account_lookup__c

Attribution to: Samuel De Rycke
This content is remixed from stackoverflow or stackexchange. Please visit https://salesforce.stackexchange.com/questions/33829