How do I create a UI for a Many-to-Many relationship?

Can anyone advise on the best way to create a UI for establishing Many-to-Many relationships ?

Lets use an example from a previous question List <<-->> Patient.

I can create two separate Table Views, one for Lists and another for Patients which will allow the user to create Lists and Patients using two开发者_如何学Python separately created Array Controllers (Lists and Patients), one linked to the List entity and other linked to the Patient entity.

Now I would like to be able to add/remove Patients from a List by creating an Table View that shows only Patients in the selected List. To do this I create a Array Controller (ListPatients) linked to the entity Patient with a Content Set binding to Lists.selection.patients.

Now things stop working nicely from here on....

If I bind a button to the ListPatients.add method then a NEW Patient gets created - there seems to be no way to simply add a NEW relationship between an existing Patient and the List.

Ideally what I would like to be able to do is to have a drop down list to select the Patient from.

Does anyone have any suggestions as to how best to do this without needing to create a new entity to represent this relationship.

What you need is a swapping Master-Detail view where either the List table or the Patient table is the Master or the Detail at any particular time.

When the List is the Master view, selecting a row will cause the Detail view to display all the Patient objects in the rowList.patients relationship. When the Patient is the Master view, selecting a row will cause the Detail view to display all the List objects in the rowPatient.lists relationship.

You really do want to break up the UI so the users always have a clear idea what the relationship is between the two tables. I would recommend a set of four tables, two each for each Master-Detail setup. That way, the user will also understand what they are looking at.

That will also make it easy to add new objects. Just put an add new button under the detail table and the user will understand that clicking it will add a new object to the relationship of the object selected in the Master view.