Lets understand what is Polymorphic Relationships. In a polymorphic relationship, the referenced object of the relationship can be one of several different types of object for example who and what field on Task and Event Object. Who can be Contact or Lead.
Relationship field and Polymorphic field
Let understand the different between Relationship field and Polymorphic field
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Relationship field
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Polymorphic field
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OwnerId field of the Account and contact object. Most of the Lookup and master-detail fields.
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OwnerId field of the event Object. It can be Calender or User. Or Who
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Example Select id, Owner.Name from Account
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Example SELECT Id, Owner.Name FROM Event WHERE Owner.Type = 'User'
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To get Parent record data use dot(.).
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You can use a TYPEOF clause in a query
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What Field is also polymorphic field on Event/Task object. What about if we need to get field base on SObject Type? We have solution of this problem : TYPEOF.
TypeOF
TYPEOF is an optional clause that can be used in a SELECT statement of a SOQL query when you’re querying data that contains polymorphic relationships. A TYPEOF expression specifies a set of fields to select that depend on the runtime type of the polymorphic reference. TYPEOF is available in API version 46.0 and later (It is also available in API version 26.0 and later as part of a Developer Preview).
Syntax:
SELECT fieldList
TYPEOF typeOfField
WHEN whenObjectType THEN whenFieldList [...]
ELSE elseFieldList
END
FROM objectType
Use Case:
On Task Object "Related To" (What) is Polymorphic field. Which can be account, opportunity or other sobject. If "Related To" (What) field is related to account then we need to get account phone and number of employees fields. If the "Related To" (WhatId) field is related to Opportunity then we need to get amount and closeDate.
Set see how we can create our query for above requirement.
SELECT
TYPEOF What
WHEN Account THEN Phone, NumberOfEmployees
WHEN Opportunity THEN Amount, CloseDate
ELSE Name
END
FROM Task
WHERE What.Type In ('Account','Opportunity')
- In this query we used TYPEOF to get runtime type of the polymorphic reference field.
- We can use the TYPE to filter our query.
Let see how to handle it in Apex Class
List<Task> listTask = [SELECT
TYPEOF What
WHEN Account THEN Phone, NumberOfEmployees
WHEN Opportunity THEN Amount, CloseDate
ELSE Name
END
FROM Task
WHERE What.Type In ('Account','Opportunity')];
for (Task tsk: listTask) {
if (tsk.What instanceof Account) {
Account acc = tsk.What;
System.debug('--acc--->'+acc.NumberOfEmployees);
} else if (tsk.What instanceof Opportunity) {
Opportunity opp = tsk.What;
System.debug('--opp--->'+opp.CloseDate);
}
}
- Use InstanceOf to check the Object Type.
