Hello everyone, 

I am using Odoo v12 and I am trying to create a function that if an item is not available it can't be selected or is removed from the list right after it is selected.

I want to show the warning message if an unavailable item is selected and also not allow the item to get added to the list.

As of right now, the item will still get added to the list and the message will pop up. I was able to clear the whole list using the commented out code [r.items = ' '], but I wanted to remove just the item that is unavailable.

Any ideas?

items = fields.Many2many('blockbuster.inventory', required=True)

@api.onchange('items')
def _verify_movie_availability(self):
    for r in self:
        for t in r.items:
            get_item_id = t.id
            if get_item_id:
                get_movie = self.env['blockbuster.inventory'].search([('id', '=', get_item_id)])
                if get_movie.available <= 0:
                    # r.items = ''
                    return {
                            'warning': {
                            'title': 'Item Unavailable',
                            'message': f'Sorry, "{get_movie.name}" is not available. Please remove it from the items list.',
                            },
                        }