from __future__ import unicode_literals
class BaseInstanceLoader(object):
"""
Base abstract implementation of instance loader.
"""
def __init__(self, resource, dataset=None):
self.resource = resource
self.dataset = dataset
def get_instance(self, row):
raise NotImplementedError
class ModelInstanceLoader(BaseInstanceLoader):
"""
Instance loader for Django model.
Lookup for model instance by ``import_id_fields``.
"""
def get_queryset(self):
return self.resource._meta.model.objects.all()
def get_instance(self, row):
try:
params = {}
for key in self.resource.get_import_id_fields():
field = self.resource.fields[key]
params[field.attribute] = field.clean(row)
return self.get_queryset().get(**params)
except self.resource._meta.model.DoesNotExist:
return None
class CachedInstanceLoader(ModelInstanceLoader):
"""
Loads all possible model instances in dataset avoid hitting database for
every ``get_instance`` call.
This instance loader work only when there is one ``import_id_fields``
field.
"""
def __init__(self, *args, **kwargs):
super(CachedInstanceLoader, self).__init__(*args, **kwargs)
pk_field_name = self.resource.get_import_id_fields()[0]
self.pk_field = self.resource.fields[pk_field_name]
ids = [self.pk_field.clean(row) for row in self.dataset.dict]
qs = self.get_queryset().filter(**{
"%s__in" % self.pk_field.attribute: ids
})
self.all_instances = dict([
(self.pk_field.get_value(instance), instance)
for instance in qs])
def get_instance(self, row):
return self.all_instances.get(self.pk_field.clean(row))