INVALID_CROSS_REFERENCE_KEY error while trying to create EntitySubscription in custom object controller

Question

So I'm getting the following erre:

FATAL_ERROR|System.DmlException: Insert failed. First exception on row 0; first error: INVALID_CROSS_REFERENCE_KEY, invalid cross reference id: []

For this code snippet -

public object__c j{get; set;}

public newcustomController(ApexPages.StandardController stdController){
    j = (object__c)stdController.getRecord();        
}

public PageReference save() {
    upsert j;



    EntitySubscription e = new EntitySubscription();
    e.SubscriberId = j.iMedia_Lead__c;
    e.parentID = j.id;
    insert e;

    PageReference jobPage = new ApexPages.StandardController(j).view();
    jobPage.setRedirect(true);
    return jobPage;
}

The idea is that the field iMedia_Lead__c is a user lookup. When someone edits a record and adds a value to the lookup field, the associated user then autofollows the record.

Any ideas what could be causing this error?

EDIT Just ot make sure I was referencing an ID object, I added the following:

public PageReference save() {
    upsert j;


    ID d = j.iMedia_Lead__c;
    EntitySubscription e = new EntitySubscription();
    e.SubscriberId = d;
    e.parentID = j.id;
    insert e;

    PageReference jobPage = new ApexPages.StandardController(j).view();
    jobPage.setRedirect(true);
    return jobPage;
}

Still no dice, but I'm pretty sure I'm passing in the ID value correctly.

EDIT 2 So after some manipulation, I am now getting this error -

Insert failed. First exception on row 0; first error: DUPLICATE_VALUE, duplicate value found: duplicates value on record with id: : []

with this code snippet:

public PageReference save() {
    upsert j;

    if(j.iMediaLead__c != null)
    {
        EntitySubscription e = new EntitySubscription();
        e.SubscriberId = j.iMediaLead__c;
        e.parentID = j.id;
        insert e;
    }
}

And the error is occuring at insert e. Any insights into this?

Answer 1

If iMedia_Lead__c is a lookup, you might be referencing the id incorrectly in the controller. Try this:

e.SubscriberId = j.iMedia_Lead__c.Id;

Update

Assuming all of the field types are correct in the assignments:

e.SubscriberId = j.iMedia_Lead__c;
e.parentID = j.id;

Since the above didn't work, my next steps in debugging would be to use System.Debug to view j.iMedia_Lead__c and j.id to verify they are as expected. After that I would try hard-coding values to verify the assignment works as expected.