If you look at activity and what it's connected to via the whatId, it's represented as a lookup. It would seem that polymorphic is closer to MDR.

Any idea what's going on there?

  • Seems like a valid point Apr 23, 2013 at 14:20
  • 3
    Polymorphic relationships are lookups, save for it can be a variety of sObjects, rather than fixed to one? Apr 23, 2013 at 15:43

1 Answer 1


Lookup is just a salesforce specific term for a foreign key relationship. Master-detail has a number of additional implications that generally are not true of polymorphic lookups.

For example, an object on the detail side of a MDR has no owner field, and is not able to participate in the sharing model; instead access to it is controller by the parent record. They're also able to use rollup summary fields and cross-object workflow.

While many polymorphic lookups cascade delete like MDRs do they don't always meet the full criteria for a MDR, and listing them as a lookup is more appropriate despite their special behavior.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.