Binding to collection of GUI elements (Lightroom)

I'm writing a plugin for Lightromm and I'm displaying list of selectable items with checkboxes. List is created basing on http data.

Now - question is how to bind to those checkboxes automatically?

I came up with such solution:

-- function called on storing property - currently unused:
local function saveSelection( propertyTable, key, val )

end

-- data
local collection = {}     -- data model
local selections          -- bindings

-- function which automatically binds to collection:
local function initSelectionBinding( context )
   selections = LrBinding.makePropertyTable(context)
   for idx, val in pairs(collection) do
      local propidx = tostring(idx)
      selections:addObserver( propidx, saveSelection )    -- not used
      selections["< contents >"][propidx] = false         -- hack to init checkboxes
   end
end

and GUI:

local rowView = {}

for idx, val in pairs(collection) do
   table.insert (rowView, 
      f:group_box {
         width = 450,
         f:row { 
            f:checkbox { value = LrView.bind{ bind_to_object = selections, key = tostring(idx) }, },
            f:static_text { title = val["state"], },
	 },
end

f:scrolled_view {
   width = 950,
   height = 500,
   f:column (rowView),
},

now, the trick is that binding is done by asigning key names as numbers converted to string.

And the same indexes must be used for data model and gui elements.

To make it easier I assigned a metatable to data model:

CollectionIndexes = function (tbl, tag)
    local i = tonumber(tag)
    if i then
        return tbl[i]
    end
    return nil
end

setmetatable(Collection, { __index = CollectionIndexes })

There is also second trick - how to access key, which is basically prop.1, prop.2, etc?
I came up with this hack to access property table elements - by looking at ["< contents >"] table:

selections["< contents >"][propidx] = false

Can it be done in nicer way?