#28519: Add `filter`, `exclude` and other base `QuerySet` methods to combined
`QuerySet`
-------------------------------------+-------------------------------------
Reporter: Stanislav | Owner: nobody
Karpov |
Type: New | Status: new
feature |
Component: Database | Version: 1.11
layer (models, ORM) | Keywords: union,
Severity: Normal | intersection, difference
Triage Stage: | Has patch: 0
Unreviewed |
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 0
UI/UX: 0 |
-------------------------------------+-------------------------------------
Hello.
I found a discussion about the filtering of combined `QuerySet` (union,
intersection, difference):
[https://github.com/django/django/pull/7727#issuecomment-269283216]
As I understood it, as a result of the discussion, it was suggested to
filter the queries before union:
If I understood your code correctly (I still did not test it), you are
still generating select * from (x union y) -- while this is more powerful
it is also unnecessary in most cases. I'd also argue that it is less
efficient, cause filtering on that result can (usually and probably
should) be pushed down to the underlying queries (when possible) to limit
the result set before joining them.
[https://github.com/django/django/pull/7727#issuecomment-269461236]
But such a decision blocks the possibility of re-use of `QuerySet`, which
is very convenient when working with `GenericForeignKey`.
**A similar example of the structure of a real project (only a structure,
not an entities).**
{{{
import typing
from django.db import models
from django.contrib.contenttypes.fields import GenericForeignKey,
GenericRelation
class Manager(models.Model):
first_name = models.CharField(max_length=255)
last_name = models.CharField(max_length=255)
class Organization(models.Model):
# pickup
title = models.CharField(max_length=255)
foundation_date = models.DateField()
manager = models.ForeignKey(Manager, on_delete=models.CASCADE)
class Warehouse(models.Model):
# pickup
organization = models.ForeignKey(Organization,
on_delete=models.CASCADE)
address = models.TextField()
class City(models.Model):
# bus
title = models.CharField(max_length=255)
code = models.CharField(max_length=10)
manager = models.ForeignKey(Manager, on_delete=models.CASCADE)
class Depot(models.Model):
# bus
title = models.CharField(max_length=255)
city = models.ForeignKey(City, on_delete=models.CASCADE)
class Garage(models.Model):
# wagon
address = models.TextField()
manager = models.ForeignKey(Manager, on_delete=models.CASCADE)
class AirbagManager(models.Manager):
def filter_by_manager__union_and_inner_join(
self, manager: typing.Union[Manager, int],
) -> models.QuerySet:
manager_id = self._clean_manager_id(manager)
return (
self
# If I'm not mistaken, now we can't direct call `union` from
`Manager`,
# but this variant increases the readability
.union(
# INNER JOIN, INNER JOIN, INNER JOIN
self.filter(pickup__warehouse__organization__manager_id=manager_id),
# INNER JOIN, INNER JOIN, INNER JOIN
self.filter(bus__depot__city__manager_id=manager_id),
# INNER JOIN, INNER JOIN
self.filter(wagon__garage__manager_id=manager_id),
)
)
def filter_by_manager__left_join(
self, manager: typing.Union[Manager, int],
) -> models.QuerySet:
# NOT WORKING (only suggestion)
manager_id = self._clean_manager_id(manager)
return self.filter(
# LEFT JOIN, LEFT JOIN, LEFT JOIN
models.Q(pickup__warehouse__organization__manager_id=manager_id)
# LEFT JOIN, LEFT JOIN, LEFT JOIN
| models.Q(bus__depot__city__manager_id=manager_id)
# LEFT JOIN, LEFT JOIN
| models.Q(wagon__garage__manager_id=manager_id),
)
def _clean_manager_id(self, manager: typing.Union[Manager, int]) ->
int:
if isinstance(manager, Manager):
return manager.id
elif isinstance(manager, int):
return manager
else:
raise ValueError
class Airbag(models.Model):
serial_number = models.CharField(max_length=255)
state = models.IntegerField()
vehicle_content_type = models.ForeignKey(
'contenttypes.ContentType',
on_delete=models.CASCADE,
)
vehicle_id = models.IntegerField(db_index=True)
vehicle = GenericForeignKey('vehicle_content_type', 'vehicle_id')
objects = AirbagManager()
class BaseVehicle(models.Model):
production_date = models.DateField()
airbags = GenericRelation(
Airbag,
object_id_field='vehicle_id',
content_type_field='vehicle_content_type',
related_query_name='%(class)s',
)
class Meta:
abstract = True
class Pickup(BaseVehicle):
carrying_kg = models.FloatField()
warehouse = models.ForeignKey(Warehouse, on_delete=models.CASCADE)
class Bus(BaseVehicle):
floors_number = models.IntegerField()
depot = models.ForeignKey(Depot, on_delete=models.CASCADE)
class Wagon(BaseVehicle):
garage = models.ForeignKey(Garage, on_delete=models.CASCADE)
Airbag.objects.filter_by_manager__union_and_inner_join(15).filter(state__gt=2)
# Expected SQL
"""
SELECT *
FROM (
(
SELECT
"airbag"."id",
"airbag"."serial_number",
"airbag"."state",
"airbag"."vehicle_content_type_id",
"airbag"."vehicle_id"
FROM "airbag"
INNER JOIN "pickup" ON ("airbag"."vehicle_id" = "pickup"."id" AND
("airbag"."vehicle_content_type_id" = 46))
INNER JOIN "warehouse" ON ("pickup"."warehouse_id" =
"warehouse"."id")
INNER JOIN "organization" ON ("warehouse"."organization_id" =
"organization"."id")
WHERE "organization"."manager_id" = 15
)
UNION
(
SELECT
"airbag"."id",
"airbag"."serial_number",
"airbag"."state",
"airbag"."vehicle_content_type_id",
"airbag"."vehicle_id"
FROM "airbag"
INNER JOIN "bus" ON ("airbag"."vehicle_id" = "bus"."id" AND
("airbag"."vehicle_content_type_id" = 49))
INNER JOIN "depot" ON ("bus"."depot_id" = "depot"."id")
INNER JOIN "city" ON ("depot"."city_id" = "city"."id")
WHERE "city"."manager_id" = 15
)
UNION
(
SELECT
"airbag"."id",
"airbag"."serial_number",
"airbag"."state",
"airbag"."vehicle_content_type_id",
"airbag"."vehicle_id"
FROM "airbag"
INNER JOIN "wagon" ON ("airbag"."vehicle_id" = "wagon"."id" AND
("airbag"."vehicle_content_type_id" = 43))
INNER JOIN "garage" ON ("wagon"."garage_id" = "garage"."id")
WHERE "garage"."manager_id" = 15
)
) AS U
WHERE U.state > 2;
"""
# VS
Airbag.objects.filter_by_manager__left_join(15).filter(state__gt=2)
# Real SQL
"""
SELECT
"airbag"."id",
"airbag"."serial_number",
"airbag"."state",
"airbag"."vehicle_content_type_id",
"airbag"."vehicle_id"
FROM "airbag"
LEFT OUTER JOIN "pickup" ON ("airbag"."vehicle_id" = "pickup"."id" AND
("airbag"."vehicle_content_type_id" = 46))
LEFT OUTER JOIN "warehouse" ON ("pickup"."warehouse_id" =
"warehouse"."id")
LEFT OUTER JOIN "organization" ON ("warehouse"."organization_id" =
"organization"."id")
LEFT OUTER JOIN "bus" ON ("airbag"."vehicle_id" = "bus"."id" AND
("airbag"."vehicle_content_type_id" = 49))
LEFT OUTER JOIN "depot" ON ("bus"."depot_id" = "depot"."id")
LEFT OUTER JOIN "city" ON ("depot"."city_id" = "city"."id")
LEFT OUTER JOIN "wagon" ON ("airbag"."vehicle_id" = "wagon"."id" AND
("airbag"."vehicle_content_type_id" = 43))
LEFT OUTER JOIN "garage" ON ("wagon"."garage_id" = "garage"."id")
WHERE (
(
"organization"."manager_id" = 15
OR "city"."manager_id" = 15
OR "garage"."manager_id" = 15
)
AND "airbag"."state" > 2
);
"""
}}}
Select from a test database containing 30 million airbags with using UNION
and INNER JOIN takes 1.1 seconds, and using LEFT JOIN - 10.0 seconds (as
the database grows, the access time will increase). PostgreSQL 9.6
(default Docker image).
--
Ticket URL: <https://code.djangoproject.com/ticket/28519>
Django <https://code.djangoproject.com/>
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