Upsert in managed package fails with DUPLICATE_VALUE - Is custom WF rule root cause?

Question

One can read about sporadic DUPLICATE_VALUE errors during Upsert in many forums. They mostly occur in Dataloader scenarios with a root cause being Oracle race conditions. But what I have here is not sporadic, but occurs every single time in a specific customer org running our managed app.

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The error occurs in a custom save action called on the EDIT page of a custom object. Clicking "Save" also update the child records using this method. I use upsert as the page needs to work for New and Edit scenarios (Should I replace it with insert / upsert?)

public PageReference doSave() {

    // Note: Required as below try/catch would prevent the platforms default behaviour to rollback on error
    Savepoint toBeforeState = Database.setSavepoint();

    // Note: Without try/catch DML errors would be shown as ugly white error page
    try {
        upsert parent;

        for(Child__c child : children) {
            if(child.Id == null) {
                child.mdr_Parent__c = parent.Id;
            }
        }

        upsert children;
    }
    catch(Exception ex) {
        ApexPages.addMessages(ex);
        Database.rollback(toBeforeState);

        // Note: Workaround for Ref.1

        removeInvalidIds();
    }

    PageReference result = (ApexPages.hasMessages()) ? null : new PageReference('/' + parent.Id);
    return result;
}

Ref.1: "Data not available" when using Database.rollback() in custom save action

This how we reproduce this error in a single customer org:

1. Save and provoke an custom (unpackaged) validation error on the packaged Child__c
2. Validation Error is displayed
3. Correct error and click save again
4. DUPLICATE_VALUE is displayed as follows

System.DmlException: Upsert failed. First exception on row 1; first error: DUPLICATE_VALUE, duplicate value found: unknown duplicates value on record with id: a0IZ0000003WUaY: []

The record of the provided Id does NOT exist after that. I guess the error comes from a Unique field on the child record which is set by a WF rule:

OR( ISNEW(), ISCHANGED( Field1__c ), ISCHANGED( Field2__c ))

Maybe ISNEW() is triggered even by an Upsert on an existing record?!

We are unable to reproduce this in our DE org (even with validation rules) BUT I can stop this error in the customer org when I turn off a workflow rule that is performing a Field Update on the same object.

Answer 1

Check how you populate the children collection. It sounds like you are adding the same object to it multiple times. Make sure you use the new keyword (as in new Child__c()) for the new items being added, and not just changing some fields on an existing object and re-adding it to the collection.