assignment to has_many through relationship does not work

For example `physician.patients = [patient1, patient2, patient3]` does not work (assuming `patients` is a `has_many :through` relationship through an appointments table.

The problem is that updating patients, implies removal of any existing records in the appointments table, *and* creation of new appointments. In fact we have to investigate what rails does if for example some appointments for a patient already exist.

At any rate it involves several operations take place.

A simplistic approach be to loop through and delete any existing records, THEN to loop through pushing the new records on.

This might be sufficient for a work around, with perhaps a warning.

A better approach might be to have a separate operation, that makes a single call to the server, the update the relationship. This has the advantage of insuring it follows rails semantics.

A third approach would be to just disallow this method, with an error message.

Input needed!