Apex Trigger Between Two Child Objects - triggers

Question

I am in the early stages of learning Apex and trying to write some code for a particular scenario. I have two custom objects called Outstanding and Transaction that are both children of an Account. I want to write a trigger that updates the end date of the Outstanding record that has a start date >= the start date on the Transaction and an end date < the end date on the Transaction. I want the end date on the correct Outstanding record to change to the end date on the Transaction.
Example:
Transaction: Start_Date__c (is changed to)= 1/2/2019
End_Date__c=1/31/2020
Outstanding Records:
Start_Date__c 1/4/2018 End_Date__c 1/4/2019
Start_Date__c 1/4/2019 End_Date__c 1/4/2020
Start_Date__c 1/4/2020 End_Date__c 1/4/2021
When the Transaction's start date is changed to 1/2/2019, I want the trigger to find the relevant Outstanding record 2 and update the end date to 12/31/2019.
Hopefully, that makes sense. If it doesn't, please let me know and I'll try to explain it again. Any help would be appreciated. Thanks.

Answer 1

You have to write a trigger on your Transaction Object on after update context. Please try the below codes.
**Trigger** :
`trigger TransactionTrigger on Transaction__c (after update) {
Map<Id,Transaction__c> accTraMap = new Map<Id,Transaction__c>();
for(Transaction__c transac : trigger.new){
accTraMap.put(transac.Account__c, transac);
}
if(!accTraMap.isEmpty()){
TransactionTriggerHandler.afterUpdate(accTraMap);
}
}`
**Class :**
public class TransactionTriggerHandler {
public static void afterUpdate(Map<Id,Transaction__c> accTransMap){
list<Outstanding__c> outstanding = [SELECT Id, Name, StartDate__c, EndDate__c, Account__c
FROM Outstanding__c where Account__c in:accTransMap.keyset()];
list<Outstanding__c> outstandingToUpdate = new list<Outstanding__c>();
for(Outstanding__c o : outstanding){
if(accTransMap.containsKey(o.Account__c)){
if(o.StartDate__c >= accTransMap.get(o.Account__c).Start_Date__c && o.EndDate__c < accTransMap.get(o.Account__c).End_Date__c){
o.EndDate__c = o.EndDate__c.toStartOfMonth().addDays(-1);
outstandingToUpdate.add(o);
}
}
}
system.debug('\n updated outstanding '+outstandingToUpdate);
if(!outstandingToUpdate.isEmpty()){
update outstandingToUpdate;
}
}
}