'Returns a dict of RequestExtensionController-s by collection.'

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

    request_ext_controllers = {}
    for req_ext in ext_mgr.get_request_extensions():
        if (req_ext.key not in request_ext_controllers.keys()):
            controller = RequestExtensionController(application)
            mapper.connect((req_ext.url_route + '.:(format)'), action='process', controller=controller, conditions=req_ext.conditions)
            mapper.connect(req_ext.url_route, action='process', controller=controller, conditions=req_ext.conditions)
            request_ext_controllers[req_ext.key] = controller
    return request_ext_controllers
