Trigger to prevent deletion of apartment if flat is associated with it

Question

I have to write a trigger to prevent deleting of Apartment records if there are flat records related to it

Here is my solution

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trigger DoNotDeleteAccountHavingRelatedContact on Apartment__c(before delete)  
{  
    for(Apartment__c acc : [SELECT Id FROM Apartment__c WHERE Id IN (SELECT Apartment__c.id FROM Flat__c) AND Id IN :Trigger.oldMap.KeySet()]){
        Trigger.oldMap.get(acc.Id).adderror('Account cannot be deleted');
    }
}

Please help..Thank u in advance

Answer 1

Assuming Apartment__c is the parent object and Flat__c is the child object, then instead of:

SELECT Apartment__c.id FROM Flat__c

you just need:

SELECT Apartment__c FROM Flat__c

because the Apartment__c field holds the Id. (Apartment__r.Id will also provide the apartment Id.)