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Code Issues 32 Releases Wiki Activity

Refs #30657 -- Made DeferredAttribute.__init__() to take a field instance instead of a field name.

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This commit is contained in:
Jon Dufresne
2019-07-23 05:04:06 -07:00
committed by Mariusz Felisiak
parent fc75694257
commit 93ffa81bc5
3 changed files with 19 additions and 20 deletions
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2
django/db/models/fields/__init__.py
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@@ -738,7 +738,7 @@ class Field(RegisterLookupMixin):
# if you have a classmethod and a field with the same name, then
# such fields can't be deferred (we don't have a check for this).
if not getattr(cls, self.attname, None):
setattr(cls, self.attname, DeferredAttribute(self.attname))
setattr(cls, self.attname, DeferredAttribute(self))
if self.choices is not None:
setattr(cls, 'get_%s_display' % self.name,
partialmethod(cls._get_FIELD_display, field=self))

24
django/db/models/query_utils.py
View File

@@ -116,8 +116,8 @@ class DeferredAttribute:
A wrapper for a deferred-loading field. When the value is read from this
object the first time, the query is executed.
"""
def __init__(self, field_name):
self.field_name = field_name
def __init__(self, field):
self.field = field
def __get__(self, instance, cls=None):
"""
@@ -127,26 +127,26 @@ class DeferredAttribute:
if instance is None:
return self
data = instance.__dict__
if data.get(self.field_name, self) is self:
field_name = self.field.attname
if data.get(field_name, self) is self:
# Let's see if the field is part of the parent chain. If so we
# might be able to reuse the already loaded value. Refs #18343.
val = self._check_parent_chain(instance, self.field_name)
val = self._check_parent_chain(instance)
if val is None:
instance.refresh_from_db(fields=[self.field_name])
val = getattr(instance, self.field_name)
data[self.field_name] = val
return data[self.field_name]
instance.refresh_from_db(fields=[field_name])
val = getattr(instance, field_name)
data[field_name] = val
return data[field_name]
def _check_parent_chain(self, instance, name):
def _check_parent_chain(self, instance):
"""
Check if the field value can be fetched from a parent field already
loaded in the instance. This can be done if the to-be fetched
field is a primary key field.
"""
opts = instance._meta
f = opts.get_field(name)
link_field = opts.get_ancestor_link(f.model)
if f.primary_key and f != link_field:
link_field = opts.get_ancestor_link(self.field.model)
if self.field.primary_key and self.field != link_field:
return getattr(instance, link_field.attname)
return None