The following describes how to use SOQL queries with polymorphic relationships in Apex. If you want more general information on polymorphic relationships, see Understanding Polymorphic Keys and Relationships in the Force.com SOQL and SOSL Reference.
List<Event> = [SELECT Description FROM Event WHERE What.Type IN ('Account', 'Opportunity')];
List<Event> = [SELECT TYPEOF What WHEN Account THEN Phone WHEN Opportunity THEN Amount END FROM Event];
Event myEvent = eventFromQuery; if (myEvent.What instanceof Account) { // myEvent.What references an Account, so process accordingly } else if (myEvent.What instanceof Opportunity) { // myEvent.What references an Opportunity, so process accordingly }
public class PolymorphismExampleClass { // Utility method for a User public static void processUser(User theUser) { System.debug('Processed User'); } // Utility method for a Group public static void processGroup(Group theGroup) { System.debug('Processed Group'); } public static void processOwnersOfMerchandise() { // Select records based on the Owner polymorphic relationship field List<Merchandise__c> merchandiseList = [SELECT TYPEOF Owner WHEN User THEN LastName WHEN Group THEN Email END FROM Merchandise__c]; // We now have a list of Merchandise__c records owned by either a User or Group for (Merchandise__c merch: merchandiseList) { // We can use instanceof to check the polymorphic relationship type // Note that we have to assign the polymorphic reference to the appropriate // sObject type before passing to a method if (merch.Owner instanceof User) { User userOwner = merch.Owner; processUser(userOwner); } else if (merch.Owner instanceof Group) { Group groupOwner = merch.Owner; processGroup(groupOwner); } } } }