diff options
Diffstat (limited to 'rest_framework/relations.py')
| -rw-r--r-- | rest_framework/relations.py | 57 |
1 files changed, 27 insertions, 30 deletions
diff --git a/rest_framework/relations.py b/rest_framework/relations.py index 75d68204..892ce6c1 100644 --- a/rest_framework/relations.py +++ b/rest_framework/relations.py @@ -84,9 +84,20 @@ class RelatedField(Field): queryset = queryset.all() return queryset - def get_iterable(self, instance, source_attrs): - relationship = get_attribute(instance, source_attrs) - return relationship.all() if (hasattr(relationship, 'all')) else relationship + def use_pk_only_optimization(self): + return False + + def get_attribute(self, instance): + if self.use_pk_only_optimization() and self.source_attrs: + # Optimized case, return a mock object only containing the pk attribute. + try: + instance = get_attribute(instance, self.source_attrs[:-1]) + return PKOnlyObject(pk=instance.serializable_value(self.source_attrs[-1])) + except AttributeError: + pass + + # Standard case, return the object instance. + return get_attribute(instance, self.source_attrs) @property def choices(self): @@ -120,6 +131,9 @@ class PrimaryKeyRelatedField(RelatedField): 'incorrect_type': _('Incorrect type. Expected pk value, received {data_type}.'), } + def use_pk_only_optimization(self): + return True + def to_internal_value(self, data): try: return self.get_queryset().get(pk=data) @@ -128,32 +142,6 @@ class PrimaryKeyRelatedField(RelatedField): except (TypeError, ValueError): self.fail('incorrect_type', data_type=type(data).__name__) - def get_attribute(self, instance): - # We customize `get_attribute` here for performance reasons. - # For relationships the instance will already have the pk of - # the related object. We return this directly instead of returning the - # object itself, which would require a database lookup. - try: - instance = get_attribute(instance, self.source_attrs[:-1]) - return PKOnlyObject(pk=instance.serializable_value(self.source_attrs[-1])) - except AttributeError: - return get_attribute(instance, self.source_attrs) - - def get_iterable(self, instance, source_attrs): - # For consistency with `get_attribute` we're using `serializable_value()` - # here. Typically there won't be any difference, but some custom field - # types might return a non-primitive value for the pk otherwise. - # - # We could try to get smart with `values_list('pk', flat=True)`, which - # would be better in some case, but would actually end up with *more* - # queries if the developer is using `prefetch_related` across the - # relationship. - relationship = super(PrimaryKeyRelatedField, self).get_iterable(instance, source_attrs) - return [ - PKOnlyObject(pk=item.serializable_value('pk')) - for item in relationship - ] - def to_representation(self, value): return value.pk @@ -184,6 +172,9 @@ class HyperlinkedRelatedField(RelatedField): super(HyperlinkedRelatedField, self).__init__(**kwargs) + def use_pk_only_optimization(self): + return self.lookup_field == 'pk' + def get_object(self, view_name, view_args, view_kwargs): """ Return the object corresponding to a matched URL. @@ -285,6 +276,11 @@ class HyperlinkedIdentityField(HyperlinkedRelatedField): kwargs['source'] = '*' super(HyperlinkedIdentityField, self).__init__(view_name, **kwargs) + def use_pk_only_optimization(self): + # We have the complete object instance already. We don't need + # to run the 'only get the pk for this relationship' code. + return False + class SlugRelatedField(RelatedField): """ @@ -349,7 +345,8 @@ class ManyRelatedField(Field): ] def get_attribute(self, instance): - return self.child_relation.get_iterable(instance, self.source_attrs) + relationship = get_attribute(instance, self.source_attrs) + return relationship.all() if (hasattr(relationship, 'all')) else relationship def to_representation(self, iterable): return [ |