[Django] #31680: Preventing DeferredAttribute .__ get__ method unnecessary calls
Django
-------------------------------------+-------------------------------------
Reporter: Sultan | Owner: nobody
Type: | Status: new
Cleanup/optimization |
Component: Database | Version: 3.1
layer (models, ORM) |
Severity: Normal | Keywords:
Triage Stage: | Has patch: 0
Unreviewed |
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 0
UI/UX: 0 |
-------------------------------------+-------------------------------------
To retrieve a deferred model attributes, the __get__ method is called
twice. This is because it uses the getattr() function, which in turn
causes the __get__ method to be called again.
{{{
def __get__(self, instance, cls=None):
"""
Retrieve and caches the value from the datastore on the first
lookup.
Return the cached value.
"""
if instance is None:
return self
data = instance.__dict__
field_name = self.field.attname
if field_name not in data:
# 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)
if val is None:
instance.refresh_from_db(fields=[field_name])
**val = getattr(instance, field_name)**
data[field_name] = val
return data[field_name]
}}}
To prevent this unnecessary call, we can simply extract the value from the
instance dict (at that moment it already contains the searched value):
{{{
def __get__(self, instance, cls=None):
"""
Retrieve and caches the value from the datastore on the first
lookup.
Return the cached value.
"""
if instance is None:
return self
data = instance.__dict__
field_name = self.field.attname
if field_name not in data:
# 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)
if val is None:
instance.refresh_from_db(fields=[field_name])
# Now the instance dict contains the reloaded data.
# Using getattr() will do extra call to __get__ method.
**val = data[field_name]**
data[field_name] = val
return data[field_name]
}}}
This reduces the number of method calls.
--
Ticket URL: <https://code.djangoproject.com/ticket/31680>
Django <https://code.djangoproject.com/>
The Web framework for perfectionists with deadlines.
Django
-------------------------------------+-------------------------------------
Reporter: Sultan | Owner: nobody
Type: | Status: new
Cleanup/optimization |
(models, ORM) |
Severity: Normal | Resolution:
Keywords: | Triage Stage:
| Unreviewed
Has patch: 1 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
-------------------------------------+-------------------------------------
Changes (by Sultan):
* has_patch: 0 => 1
* easy: 0 => 1
--
Ticket URL: <https://code.djangoproject.com/ticket/31680#comment:1>
Django
-------------------------------------+-------------------------------------
Reporter: Sultan | Owner: nobody
Type: | Status: new
Cleanup/optimization |
(models, ORM) |
Severity: Normal | Resolution:
Keywords: | Triage Stage:
| Unreviewed
Needs tests: 0 | Patch needs improvement: 0
-------------------------------------+-------------------------------------
Description changed by Sultan:
Old description:
New description:
To retrieve a deferred model attributes, the __get__ method is called
twice. This is because it uses the getattr() function, which in turn
causes the __get__ method to be called again.
{{{
def __get__(self, instance, cls=None):
"""
Retrieve and caches the value from the datastore on the first
lookup.
Return the cached value.
"""
if instance is None:
return self
data = instance.__dict__
field_name = self.field.attname
if field_name not in data:
# 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)
if val is None:
instance.refresh_from_db(fields=[field_name])
**val = getattr(instance, field_name)**
data[field_name] = val
return data[field_name]
}}}
To prevent this unnecessary call, we can simply extract the value from the
instance dict (at that moment it already contains the reloaded value):
{{{
def __get__(self, instance, cls=None):
"""
Retrieve and caches the value from the datastore on the first
lookup.
Return the cached value.
"""
if instance is None:
return self
data = instance.__dict__
field_name = self.field.attname
if field_name not in data:
# 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)
if val is None:
instance.refresh_from_db(fields=[field_name])
# Now the instance dict contains the reloaded data.
# Using getattr() will do extra call to __get__ method.
**val = data[field_name]**
data[field_name] = val
return data[field_name]
}}}
This reduces the number of method calls.
--
--
Ticket URL: <https://code.djangoproject.com/ticket/31680#comment:2>
Django
-------------------------------------+-------------------------------------
Reporter: Sultan | Owner: Sultan
Type: | Status: assigned
Cleanup/optimization |
Component: Database layer | Version: master
(models, ORM) |
Severity: Normal | Resolution:
Has patch: 1 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
-------------------------------------+-------------------------------------
* owner: nobody => Sultan
* status: new => assigned
* version: 3.1 => master
* stage: Unreviewed => Accepted
Comment:
It looks that `val = getattr(instance, field_name)` is redundant.
--
Ticket URL: <https://code.djangoproject.com/ticket/31680#comment:3>
Django
-------------------------------------+-------------------------------------
Reporter: Sultan | Owner: Sultan
Type: | Status: assigned
Cleanup/optimization |
Component: Database layer | Version: master
(models, ORM) |
Severity: Normal | Resolution:
Keywords: | Triage Stage: Accepted
Needs tests: 0 | Patch needs improvement: 0
-------------------------------------+-------------------------------------
--
Ticket URL: <https://code.djangoproject.com/ticket/31680#comment:4>
Django
-------------------------------------+-------------------------------------
Reporter: Sultan | Owner: Sultan
Type: | Status: assigned
Cleanup/optimization |
Component: Database layer | Version: master
(models, ORM) |
Severity: Normal | Resolution:
Keywords: | Triage Stage: Accepted
Needs tests: 0 | Patch needs improvement: 0
-------------------------------------+-------------------------------------
Comment (by Sultan):
Replying to [comment:4 felixxm]: Yes you are right. I changed the code.
Now it has become much easier and better. Thank you.
{{{
def __get__(self, instance, cls=None):
"""
Retrieve and caches the value from the datastore on the first
lookup.
Return the cached value.
"""
if instance is None:
return self
data = instance.__dict__
field_name = self.field.attname
if field_name not in data:
# 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)
if val is None:
instance.refresh_from_db(fields=[field_name])
else:
data[field_name] = val
return data[field_name]
}}}
--
Ticket URL: <https://code.djangoproject.com/ticket/31680#comment:5>
Django
-------------------------------------+-------------------------------------
Reporter: Sultan | Owner: Sultan
Cleanup/optimization |
Component: Database layer | Version: master
(models, ORM) |
Keywords: | Triage Stage: Accepted
Has patch: 1 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
-------------------------------------+-------------------------------------
* status: assigned => closed
* resolution: => fixed
Comment:
In [changeset:"678c8dfee458cda77fce0d1c127f1939dc134584" 678c8df]:
{{{
#!CommitTicketReference repository=""
revision="678c8dfee458cda77fce0d1c127f1939dc134584"
Fixed #31680 -- Removed unnecessary getattr() call in
DeferredAttribute.__get__().
refresh_from_db() loads fields values.
}}}
--
Ticket URL: <https://code.djangoproject.com/ticket/31680#comment:6>