how to Query parent to child

Question

I have process in salesforce in such a way opportunity we can relate this opportunity to this lookup field parent_opportunity__c . Which relates opportunity to other parent opportunity.

I want to write a query parent to child :

select id,(select id from opportunity where parent_opportunity__c!=null) from opportunity where parent_opportunity__c=null

I have worked with different scenarios i cant able to crack it

select id,name,(select id,name from parent_opportunity__r) from opportunity this is showing error and

select id,name,(select id,name from opportunity) from parent_opportunity__c this is also error

Answer 1

You need the PLURAL of the parent_opportunity object name.

Given that your object is called parent_opportunity__c, it's likely your relationship is called something like child_opportunities__r. You can check this on the lookup field that defines this relationship.

Once you have that, use this field in your query - it should work.

You can see in the image of the definition of a lookup that the relationship from parent to child is Screenings__r and from child back up to Opportunity is Opportunity (as there is only one)