catch old field values of parent object from child object's trigger in master detail relationship

Question

i have trigger on custom child object seasonAddress and it has Masterdetail relationship with contact object. if current season address record is marked as invalid, parent contact record is get updated with the address fields of earlier valid address field values of contact. So i need get the old version of contact records in 'before update trigger' on seasonaddress object.. how can we achive this please help me..

Answer 1

Assuming you're manually determining whether the address is valid or not, you'd need to fire a trigger based on a "invalid address" flag on the Contact record and access the Contact__Histories object to access the previous value of that field.

This is of course assuming that you are tracking the history of that field on the Contact object.

So, to Summarize, you need to make sure you're tracking the field history of the address field on the Contact object and then fire your trigger on the "Address is invalid" action and query Contact__Histories and loop over that collection to get the most recent address value and then update your Contact record with that address.

Answer 2

In the update context, you can access the

trigger.old

or

trigger.oldMap

system variables to get the fields from the object before the update occurs. An example of using this is

for (SObject s: trigger.new){
    SObject oldS = trigger.oldMap.get(s.id);
    //do stuff
}

After getting the old object, you can get the Contact that matches this object and set the field to that old value.