def _build_requested_prefetches(self, prefetches, requirements, model,
fields, filters, is_root_level):
"""Build a prefetch dictionary based on request requirements."""
meta = Meta(model)
for name, field in six.iteritems(fields):
original_field = field
if isinstance(field, dfields.DynamicRelationField):
field = field.serializer
if isinstance(field, serializers.ListSerializer):
field = field.child
if not isinstance(field, serializers.ModelSerializer):
continue
source = field.source or name
if '.' in source:
raise ValidationError('Nested relationship values '
'are not supported')
if source == '*':
# ignore custom getter/setter
continue
if source in prefetches:
# ignore duplicated sources
continue
related_queryset = getattr(original_field, 'queryset', None)
if callable(related_queryset):
related_queryset = related_queryset(field)
is_id_only = getattr(field, 'id_only', lambda: False)()
is_remote = meta.is_field_remote(source)
is_gui_root = self.view.get_format() == 'admin' and is_root_level
if (related_queryset is None and is_id_only and not is_remote
and not is_gui_root):
# full representation and remote fields
# should all trigger prefetching
continue
# Popping the source here (during explicit prefetch construction)
# guarantees that implicitly required prefetches that follow will
# not conflict.
required = requirements.pop(source, None)
query_name = Meta.get_query_name(original_field.model_field)
prefetch_queryset = self._build_queryset(serializer=field,
filters=filters.get(
query_name, {}),
queryset=related_queryset,
requirements=required)
# There can only be one prefetch per source, even
# though there can be multiple fields pointing to
# the same source. This could break in some cases,
# but is mostly an issue on writes when we use all
# fields by default.
prefetches[source] = Prefetch(source, queryset=prefetch_queryset)
return prefetches
def _build_queryset(self,
serializer=None,
filters=None,
queryset=None,
requirements=None):
"""Build a queryset that pulls in all data required by this request.
Handles nested prefetching of related data and deferring fields
at the queryset level.
Arguments:
serializer: An optional serializer to use a base for the queryset.
If no serializer is passed, the `get_serializer` method will
be used to initialize the base serializer for the viewset.
filters: An optional TreeMap of nested filters.
queryset: An optional base queryset.
requirements: An optional TreeMap of nested requirements.
"""
is_root_level = False
if serializer:
if queryset is None:
queryset = serializer.Meta.model.objects
else:
serializer = self.view.get_serializer()
is_root_level = True
model = serializer.get_model()
if not model:
return queryset
meta = Meta(model)
prefetches = {}
# build a nested Prefetch queryset
# based on request parameters and serializer fields
fields = serializer.fields
if requirements is None:
requirements = TreeMap()
self._get_implicit_requirements(fields, requirements)
if filters is None:
filters = self._get_requested_filters()
# build nested Prefetch queryset
self._build_requested_prefetches(prefetches, requirements, model,
fields, filters, is_root_level)
# build remaining prefetches out of internal requirements
# that are not already covered by request requirements
self._build_implicit_prefetches(model, prefetches, requirements)
# use requirements at this level to limit fields selected
# only do this for GET requests where we are not requesting the
# entire fieldset
is_gui = self.view.get_format() == 'admin'
if ('*' not in requirements and not self.view.is_update()
and not self.view.is_delete() and not is_gui):
id_fields = getattr(serializer, 'get_id_fields', lambda: [])()
# only include local model fields
only = [
field for field in set(id_fields + list(requirements.keys()))
if meta.is_field(field) and not meta.is_field_remote(field)
]
queryset = queryset.only(*only)
# add request filters
query = self._filters_to_query(filters)
if query:
# Convert internal django ValidationError to
# APIException-based one in order to resolve validation error
# from 500 status code to 400.
try:
queryset = queryset.filter(query)
except InternalValidationError as e:
raise ValidationError(
dict(e) if hasattr(e, 'error_dict') else list(e))
except Exception as e:
# Some other Django error in parsing the filter.
# Very likely a bad query, so throw a ValidationError.
err_msg = getattr(e, 'message', '')
raise ValidationError(err_msg)
# A serializer can have this optional function
# to dynamically apply additional filters on
# any queries that will use that serializer
# You could use this to have (for example) different
# serializers for different subsets of a model or to
# implement permissions which work even in sideloads
if hasattr(serializer, 'filter_queryset'):
queryset = serializer.filter_queryset(queryset)
# add prefetches and remove duplicates if necessary
prefetch = prefetches.values()
queryset = queryset.prefetch_related(*prefetch)
if has_joins(queryset) or not is_root_level:
queryset = queryset.distinct()
if self.DEBUG:
queryset._using_prefetches = prefetches
return queryset
