:date: 2017-09-09

===========================
Saturday, September 9, 2017
===========================

A new way for disabling actions per row
=======================================

It is now possible to disable an action by adding its name to the set
returned by :meth:`disabled_fields
<lino.core.model.Model.disabled_fields>`.

This approach can be more intuitive to write and less costly to run.
For example the three actions on :class:`lino_xl.lib.stars.Starrable`
are now implemented using this new possibility.

Here is a fictive example

1. Using :meth:`get_action_permission
   <lino.core.actions.Action.get_action_permission>` method of the
   action::

    class DoOne(dd.Action):
        ...
        def get_action_permission(self, ar, obj, st):
            for x in obj.foos.all():
                if x.bar:
                    return False
            return super(DoOne, self).get_action_permission(ar, obj, st)

    class Foo(dd.Model):
        do_one = DoOne()

2. Using the :meth:`disabled_fields
   <lino.core.model.Model.disabled_fields>` method of the model which
   defines the action::

    class DoOne(dd.Action):
        ...
        # no get_action_permission()

    class Foo(dd.Model):

        do_one = DoOne()

        def disabled_fields(self, ar):
            s = super(Foo, self).disabled_fields(ar)
            for x in self.foos.all():
                if x.bar:
                    s.add("do_one")
            return s

No more method `disabled_actions` : actions share the same namespace
as fields, so there was no need to separate them. A side effect of
this is that in readonly tables it is no longer possible to disable
individual actions. Which AFAICS is correct.

In :xfile:`linoweb.js`, I replaced "disabled_actions" by
"disabled_fields". For example::
  
      var da = record.data.disabled_actions;

becomes::      
      
      var da = record.data.disabled_fields;

One challenge were actions with an `allowed_states`.  These are now
handled more efficiently. Lino analyses the situation once at startup
and creates per actor a dict :attr:`_state_to_disabled_actions` which
is then being used for disabling these actions based on the row's
state.