Apex object field for reverse lookup

Question

Let's say I have 2 custom objects: Person and Award. Award has a lookup field to Person called Receiver.

If I query an object of Award, I know I can do Award.Receiver__r to access fields of the related Person. Is it possible to do the reverse - provided I know that a specific Person object has an Award (i.e. an Award exists whose lookup field specifies that person), can I access the fields of that Award via a field on Person object in Apex and/or SOQL?

Answer 1

Yes. You are looking for a Left Outer Join, where the type of query you first reference is a Right Outer Join. Your query might look like:

SELECT (SELECT Id FROM Awards__r) FROM Person__c

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You can control the value of this Child Relationship Name in the configuration on the lookup field. Custom lookups append __r to the relationship name. When configuring the lookup definition, this option will be on Step 3 of the configuration wizard.

You can also change it later by editing the field.

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You can verify the child relationship to use programmatically (where I guessed it might be Awards__r) using this snippet in Execute Anonymous:

for (ChildRelationship relation : SObjectType.Person__c.getChildRelationships())
    if (relation.getChildSObject() == Award__c.sObjectType)
        system.debug(relation.getRelationshipName()); // use this output verbatim

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Note that while you can treat this sub-query like a field, it contains a List<Award__c> in this instance.

Person somePerson = [SELECT (SELECT Id FROM Awards__r) FROM Person__c LIMIT 1];
List<Award__c> awards = somePerson.Awards__r;
// you can also get it dynamically
awards = somePerson.getSObjects('Awards__r');