Can I create a polymorphic key from a custom object?

Hi Himanshu,

I found an idea for the above requirement. Please find the link of idea:

https://success.salesforce.com/ideaview?id=08730000000BqzBAAS

To mimic the functionality by say using a custom text field, would be a rigorous customization: Custom text field, mark as “ExternalId” for indexing purpose.

Thanks