class _Nexus(object):
"""
Internal to Actuator
A nexus is where, for a given instance of a system, models and their
instances can be recorded and then looked up by other components. In
particular, model instances can be looked up by either the class of the
instance, or by a base class of the instance. This way, one model instance can
find another instance by way of the instance class or base class. This can
be used when processing reference selection expressions or context
expressions.
"""
def __init__(self):
self.mapper = ClassMapper()
def capture_model_to_instance(self, model_class, instance):
"""
Associate a model class to an instance of that class. Actually causes a series
of associations to be created, following the inheritance chain for the
class and mapping each base class to the instance, as we can't be sure
which class will be used to try to locate the instance, the specific one
or a more general one. Mapping terminates when ModelBase is encountered
in the mro.
"""
self.mapper[model_class] = instance
for base in model_class.__mro__:
if base in [ModelBase, _NexusMember]:
break
if issubclass(base, (ModelBase, _NexusMember)):
self.mapper[base] = instance
def find_instance(self, model_class):
return self.mapper.get(model_class)
def merge_from(self, other_nexus):
self.mapper.update(other_nexus.mapper)
def __init__(self):
self.mapper = ClassMapper()
