External Object RelationShip

Question

I have 2 External Objects "Orders and OrderDetails" I want to create External LookUp relationship between "Orders and OrderDetails".

I read some where that "To create External LookUp relationhip/Indirect relationship parent should have a field with ExternalId and Unique features". If it is a standard/Custom object it's easy to edit the field and make as ExternalId and Unique.

When i'm trying to make a "ExternalId and Unique" for field in OrderDetails, there is no such option to check for OrderDetails, may be because of OrderDetails is an external Object.

1.But what can i do so that the field become Unique and ExternalId?

2.or else ExternalId and Unique need to be created in the External System(I mean in SQLServer) itself

Answer 1

You can only use an External Lookup to reference another external object. In that case, it references the ExternalId standard field on the target domain. You don't have to declare it unique, an object's ID is always assumed to be unique. Also, uniqueness on an External Object is determined by the external data source, and not controllable within Salesforce, which is why you won't find the "Unique" attribute on the field for an external object.

An indirect lookup has to have a field with ExternalId and Unique attributes set, but it can only point to a standard or custom object. That's a different use case: it's used for referencing a standard or custom object FROM an external data source that doesn't store Salesforce record IDs.