Traverse objects in a single SOQL

Question

There are 2 child objects for Account object, namely AccChild1 and AccChild2. Is it possible to traverse from AccChild2 to Account object, and then from Account to AccChild1 object in a single SOQL query?

This is something like: Child1 --> Parent --> Child2

Answer 1

Answer is yes, you can do it one soql.

List<Account> accts = [
    select Id, (
        select Id from AccChildren2__r
        )
    from Account
    where Id in (
        select Account__c from AccChild1__c
        )
    ];

for(Account acct :accts){
    List<AccChild2__c> children2 = acct.AccChildren2__r;
    //do something
}

Pay attention, that you need to specify correct child relationship name for AccChild2__c sobject from Account. refer to Understanding Relationship Names, Custom Objects, and Custom Fields