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Mammu Custom Object relationship query?
[SELECT MailingStreet, MailingCity, AccountId FROM Contact WHERE AccountId IN : acctIds] In this query we will retrieve Contacts based on Account IDs, I want to implement the same functinality using Custom Object Where Parent object is Campsite__c and Child Object is Campsite_Reservation__c. Can any body write the query? And anyone explain when to use __r and __c
Create a set that saves all your parent object id. i.e parentObjectIdSet.
The use the following query,
if the parent field name on child object is Campsite__c then,
[select id, name, field1__c from Campsite_Reservation__c where Campsite__c in: parentObjectIdSet];
This is to retrive particular child records.
To accomplish your requirement, there are two Methods for writing the SOQL :
Method 1 - Child-to-parent relationship, we can use dot notation to access the parent object fields
In this method your query would be like this,
list<Campsite_Reservation__c> campSiteReservations = [SELECT Id,field_Name__c,Campsite__r.field1__c from Campsite_Reservation__c where Campsite__c In :campSiteIds ]
,or
list<Campsite_Reservation__c> campSiteReservations = [SELECT Id,field_Name__c,Campsite__r.field1__c from Campsite_Reservation__c WHERE Campsite__r.Id In :campSiteIds]
Method 2 - Parent-to-child relationship queries do not use dot notation
list<Campsite__c> campSites = [SELECT Id,field1__c,(SELECT Id,field_Name__c FROM Campsite_Reservation__r) FROM Campsite__c In :campSiteIds];
list<Campsite_Reservation__r> campSiteReservations = new list<Campsite_Reservation__r>();
for(Campsite__c tempObj : campSites ){
campSiteReservations.addAll(tempObj.Campsite_Reservation__r);
}
Now, the use of "__r" and "__c":
As can be seen from the Method 1, "__r" is used when we need to access the fields of the parent object in the Child-to-parent relationship SOQL, like "Campsite__r.Id " in your case.
As from the Method 2, "__r" is also used in case when getting the child records using inner query.
NOTE : in method 2, "__r" is not used with the fields of the child object and parent object.
I think this clarified your questions.
Please go through this link http://www.salesforce.com/us/developer/docs/soql_sosl/Content/sforce_api_calls_soql_relationships_and_custom_objects.htm#sforce_api_calls_soql_relationships_and_custom_objects
for more understanding.
Thanks