Moving this back to under review.
Will you please give us more information on your use case for this request?
I'm working on multitenant application so my PK consists of ProductId (identity) and TenantId and there is no way to set PK as ProductId only.
But I've succeeded to solve the problem by using MetadataStore.registerEntityTypeCtor and defining own initialization function that filled PK fields.
Then I've faced the other problem "Internal Error in key fixup - unable to locate entity" and solved it by replacing EntityGroup._fixupKey function with my custom function with only one changed string:
var ix = this._indexMap[tempValue + ":::" + TenantId];
I guess it would be very helpful if you describe this way somewhere in the doc.frizzyH commented
The problem is not resolved. It just says that you can not use multipart keys with Breeze.