Serializing django-mptt trees in Tastypie - django

Question

How do I serialize django-mptt trees in Tastypie?
I want to use django-mptt's cache_tree_children(). I've tried applying in different Tastypie hooks, but it throws an error.

Answer 1

Without the cache_tree_children method you could probably have your children serialized by simply hooking up a ToManyField with full=True pointing at the children property:
class MenuResource(ModelResource):
children = fields.ToManyField('self', 'children', null=True, full=True)
parent = fields.ToOneField('self', 'parent', null=True)
class Meta:
queryset = Menu.objects.all()
To implement the cache_tree_children function you could write your own ToManyField subclass that overrides the standard dehydrate function. Please note, that I only tested this solution very superficially:
def dehydrate(self, bundle):
if not bundle.obj or not bundle.obj.pk:
if not self.null:
raise ApiFieldError("The model '%r' does not have a primary key and can not be used in a ToMany context." % bundle.obj)
return []
the_m2ms = None
previous_obj = bundle.obj
attr = self.attribute
if isinstance(self.attribute, basestring):
attrs = self.attribute.split('__')
the_m2ms = bundle.obj
for attr in attrs:
previous_obj = the_m2ms
try:
the_m2ms = getattr(the_m2ms, attr, None)
except ObjectDoesNotExist:
the_m2ms = None
if not the_m2ms:
break
elif callable(self.attribute):
the_m2ms = self.attribute(bundle)
if not the_m2ms:
if not self.null:
raise ApiFieldError("The model '%r' has an empty attribute '%s' and doesn't allow a null value." % (previous_obj, attr))
return []
self.m2m_resources = []
m2m_dehydrated = []
# There goes your ``cache_tree_children``
for m2m in cache_tree_children(the_m2ms.all()):
m2m_resource = self.get_related_resource(m2m)
m2m_bundle = Bundle(obj=m2m, request=bundle.request)
self.m2m_resources.append(m2m_resource)
m2m_dehydrated.append(self.dehydrate_related(m2m_bundle, m2m_resource))
return m2m_dehydrated
One of the main advantages of this method is that you don't have to care about detail / list view constraints / differences no more. You even can parameterize this aspect of your resource further down until you got some kind of default behavior that fits your needs. Field-based, that is. Which I think is cool.

Answer 2

This is how I solved it:
class MenuResource(ModelResource):
parent = fields.ForeignKey('self', 'parent', null=True)
class Meta:
serializer = PrettyJSONSerializer()
queryset = Menu.objects.all().select_related('parent')
include_resource_uri = False
fields = ['name']
def get_child_data(self, obj):
data = {
'id': obj.id,
'name': obj.name,
}
if not obj.is_leaf_node():
data['children'] = [self.get_child_data(child) \
for child in obj.get_children()]
return data
def get_list(self, request, **kwargs):
base_bundle = self.build_bundle(request=request)
objects = self.obj_get_list(bundle=base_bundle,
**self.remove_api_resource_names(kwargs))
sorted_objects = self.apply_sorting(objects, options=request.GET)
paginator = self._meta.paginator_class(
request.GET, sorted_objects,
resource_uri=self.get_resource_uri(), limit=self._meta.limit,
max_limit=self._meta.max_limit,
collection_name=self._meta.collection_name
)
to_be_serialized = paginator.page()
from mptt.templatetags.mptt_tags import cache_tree_children
objects = cache_tree_children(objects)
bundles = []
for obj in objects:
data = self.get_child_data(obj)
bundle = self.build_bundle(data=data, obj=obj, request=request)
bundles.append(self.full_dehydrate(bundle))
to_be_serialized[self._meta.collection_name] = bundles
to_be_serialized = self.alter_list_data_to_serialize(request,
to_be_serialized)
return self.create_response(request, to_be_serialized)
If you're not using pagination you can just take that part out. That's what I did.