Apex Trigger For New Child From Field Update

Question

My goal is to enable my team to update a particular field on the Opportunity Object (Stage__c) to 'Closed Won', and have that auto-generate a new custom child object (Onboarding) that is linked to the same account that the Opportunity is linked to.

At this point, I have produced the following trigger but am continuously prompt with

"Error: Compile Error: Invalid field Stage__c for SObject Opportunity at line 6 column 17"

Below is my entire trigger. Any thoughts/advice are greatly appreciated!

trigger CreateOB on Account (after insert, after update) {
    Onboarding__c[] inserts = new Onboarding__c[] {};
    for (Opportunity a : Trigger.new) {
        if (a.Stage__c == 'Closed Won') {
            Account old = Trigger.oldMap.get(a.Id);
            if (a.Stage__c != old.Stage__c) {
                inserts.add(new Onboarding__c(Account_Name__c = a.Id));
            }
        }
    }
    insert inserts;
}

Answer 1

Your Trigger is on account but you are Assigning trigger.new to the Opportunity sObject in your for loop

The error means there is no field named Stage__c on the Opportunity Object

Are you sure you have created a custom field named Stage? Or are you trying to update the standard field Stage. If the latter, the API name of the standard Field is StageName

It may also be fixed by changing Opportunity to Account in the for loop as that may be what you meant to have. (Only if Stage__c exists on Account

Answer 2

Since your trigger is on the Account object, your trigger.new list will contain a list of accounts that the trigger is running on. So you're basically trying to check the Stage__c field on the Account object, which doesn't exist.

Not sure what your process is, but 2 options are available here:

1) Change your trigger to be on Opportunity

2) Replace trigger.new with a SOQL query in order to obtain the opportunity's Stage__c field:

for (Account a : [SELECT Id, Opportunity.Stage__c FROM Account WHERE Id IN :trigger.newMap.keySet()])

and then

if (a.Opportunity.Stage__c == 'Closed Won') // your code here