I am trying to load data via talend ETL, where my Related to (whatId) is a lookup on a custom object's external id.

I am stuck, and I believe i have everything set up correctly

my salesforce shows the custom module in the lookup list enter image description here

and my etl is setup like so

enter image description here

but ther error i am receiving is this

InvalidBatch : Entity type for the polymorphic foreign key reference: What didn't match the supplied type: Contact_Report__c

I checked the fields just in case I am matching string to string, so thats not it

I did not setup the objects, not sure how they got contact report (custom object) in the task lookup for what, but maybe something is missing there?

I'm pretty stumped, any and all help is greatly appreciated

2 Answers 2


It doesn't seem possible as of now, to use external Id feature while upserting the tasks, but an Idea has been raised already for the same. https://success.salesforce.com/ideaview?id=08730000000Br0QAAS

You may want to upvote the same.

Hope this helps :)

  • so, i suppose i could pass in a salesforce id to the whatid instead of the external, correct?
    – Jay Rizzi
    Commented May 25, 2017 at 14:52
  • That's absolutely correct :) Commented May 25, 2017 at 14:52
  • It does seem possible, please check my answer. We just made this work that way.
    – xouns
    Commented Apr 15, 2022 at 19:04

Please check this answer, this also worked for us. In Talend, remove the '__c' postfix from the Entity Name (the SObject).


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