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cocoadata-bindingcore-datansarraycontroller

Bind a NSSet representing a to-many relationship to the selection of a NSArrayController

Here's the scenario. There are two CoreData model objects, A and B, and the relationship between them is that A has-many B, represented by the property setOfBs. I'd like to display two tables, one listing all the As (Table 1), another listing all the Bs (Table 2). As the user selects items in Table 1, the selection in Table 2 changes to reflect the value of setOfBs of the A selected in Table 1. The content of the table doesn't change, only the selection changes. And if the selection in Table 1 changes, it would change the setOfBs to reflect that.

Can this be accomplished using bindings? Or would custom logic be required?

Solution

  • I believe you will have to write additional logic to get this approach to work. Here's why: The selection bindings for NSArrayControllers (and all the UI objects that bind to them) are based on selection indexes but when you have an object of type A, it vends a set of B objects. Assuming you have an array controller for As and an array controller for Bs, you need a way to get from those objects to their indexes in the array of Bs in order to set the selection of the array controller for B. This isn't hard code to write, but I don't believe you'll be able to do this with bindings alone.

    That said, as you speculated in your comment, this doesn't seem like a good way to edit this relationship. In the common case, TableView selection is UI state, and not model state. If you build a UI like you describe, UI state and model state become the same thing. I'm not saying it's impossible, or inherently bad, but it's not really a "standard" way to do this sort of thing. One common pattern looks like this:

    To-many editing UI example

    Even an approach like this will require additional logic, because there appears to not be a way (out of the box) to bind to "All Bs not in the selected A's setOfBs" without writing code. Again, not difficult code to write, but it's not clear to me that this can be done with bindings alone. I could be wrong, but that's my reading of the situation.