'Load related resources, which are defined via a ``has``
relationship but conceptually come in two forms:
1. A reference, which is a related resource instance and can be
``None``, such as an EC2 instance\'s ``vpc``.
2. A subresource, which is a resource constructor that will always
return a resource instance which shares identifiers/data with
this resource, such as ``s3.Bucket(\'name\').Object(\'key\')``.'

def _load_has_relations(self, attrs, resource_name, resource_model, service_context):

    for reference in resource_model.references:
        attrs[reference.name] = self._create_reference(reference_model=reference, resource_name=resource_name, service_context=service_context)
    for subresource in resource_model.subresources:
        attrs[subresource.name] = self._create_class_partial(subresource_model=subresource, resource_name=resource_name, service_context=service_context)
    self._create_available_subresources_command(attrs, resource_model.subresources)
