Custom `hydrate_m2m` method to workaround tastypie bug on creating model with dependent model

YouModelResource.py

# Say, you have models `Invoice` and `InvoicePart`. The `InvoicePart` 
# has a non-nullable field of `Invoice`. 
#
# Currently (August 2012), `tastypie` will throw an error when you try 
# to create (`HTTP Post`) a new `Invoice` that contains one or more new 
# `InvoicePart`.
# 
# The problem is that when `tastypie` processes the `InvoicePart`, the
# backlink to `Invoice` is not set.
# 
# The following custom method worked around the problem. Let me know if
# you find it useful.

class YourModelResource(ModelResource):

    def get_backlink(self, field_object):
        cls = field_object.to_class()
        for cls_field_name, cls_field_object in cls.fields.items():
            if not getattr(cls_field_object, 'is_related', False):
                continue

            if cls_field_name == self.Meta.resource_name:
                if cls_field_object.to_class().Meta == self.Meta:
                    return cls_field_name, cls_field_object
            
        return None, None

    def hydrate_m2m(self, bundle):
        if bundle.obj is not None and bundle.obj.pk is not None:
            uri = self.get_resource_uri(bundle.obj)
            
            for field_name, field_object in self.fields.items():
                if not getattr(field_object, 'is_m2m', False):
                    continue
                
                backlink_name, backlink_object = self.get_backlink(field_object)
                if backlink_object is not None:
                    related_objects = (bundle.data[field_name] 
                                if field_name in bundle.data else [])
                    for related in related_objects:
                        if not backlink_name in related:
                            related[backlink_name] = uri 
        return super(ModelResource, self).hydrate_m2m(bundle)

Turned out the problem was caused by missing related_name.

Got inspired by answer here:
http://stackoverflow.com/questions/10582449/creating-related-resources-with-tastypie