'Return a dict of ActionExtensionController-s by collection.'

def _action_ext_controllers(self, application, ext_mgr, mapper):

    action_controllers = {}
    for action in ext_mgr.get_actions():
        if (action.collection not in action_controllers.keys()):
            controller = ActionExtensionController(application)
            mapper.connect(('/%s/:(id)/action.:(format)' % action.collection), action='action', controller=controller, conditions=dict(method=['POST']))
            mapper.connect(('/%s/:(id)/action' % action.collection), action='action', controller=controller, conditions=dict(method=['POST']))
            action_controllers[action.collection] = controller
    return action_controllers
