Apex Trigger For New Child From Field Update - Update 2

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.

Now the problem seems to be that I am attempting to create an Onboarding page (custom child obj) from a field change on the Opportunity page (child obj) and have the new Onboarding page linked to the same Account that the Opportunity was linked to.

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

I am able to save the code but am receiving the following error on the Opportunity page when I attempt to submit it with the StageName = Closed Won:

Error:Apex trigger CreateOB caused an unexpected exception, contact your administrator: CreateOB: execution of AfterUpdate caused by: System.DmlException: Insert failed. First exception on row 0; first error: FIELD_INTEGRITY_EXCEPTION, Account Name: id value of incorrect type: 00611000007THcnAAG: [Account_Name__c]: Trigger.CreateOB: line 11, column 1

Answer 1

Instead of:

inserts.add(new Onboarding__c(Account_Name__c = a.Id));

you probably need:

inserts.add(new Onboarding__c(Account_Name__c = a.AccountId));

(assuming Onboarding__c.Account_Name__c is a lookup to objects of type Account).

Probably worth changing the variable from a to o to make the code a bit clearer.

Answer 2

An alternative to this trigger is to use the new process builder, you should be able to open a case with SalesForce and ask for it to be turned on in your org, it's still beta. Once it is turned on you will find "Processes" on the setup page under the "Workflow and Approvals" menu.
I stepped through creating a related task similar to what you would do for the onboarding record.
Click the "New Process" button and give it a name/description.
Click on the "Add Object" component and select the Opportunity object.
Enter your criteria similar to a workflow rule
Then click on the "Immediate Action" component and select create new record and prepopulate the fields. Clicking on the pencil next to the field allows you to use another field's values.