Alasdair's answer jest pomocna, ale nie podoba mi się użycie distinct()
. Czasami może się przydać, ale zwykle jest to zapach kodu, który mówi, że zawiodłeś swoje połączenia.
Na szczęście narzędzie Django pozwala na filtrowanie podzapytań.
Oto kilka sposobów, aby uruchomić zapytania z pytaniem:
# Tested with Django 1.9.2
import logging
import sys
import django
from django.apps import apps
from django.apps.config import AppConfig
from django.conf import settings
from django.db import connections, models, DEFAULT_DB_ALIAS
from django.db.models.base import ModelBase
NAME = 'udjango'
def main():
setup()
class User(models.Model):
email = models.EmailField()
def __repr__(self):
return 'User({!r})'.format(self.email)
class Report(models.Model):
user = models.ForeignKey(User)
syncdb(User)
syncdb(Report)
anne = User.objects.create(email='[email protected]')
User.objects.create(email='[email protected]')
alice = User.objects.create(email='[email protected]')
User.objects.create(email='[email protected]')
Report.objects.create(user=anne)
Report.objects.create(user=alice)
Report.objects.create(user=alice)
logging.info('users without reports')
logging.info(User.objects.filter(report__isnull=True, email__startswith='a'))
logging.info('users with reports (allows duplicates)')
logging.info(User.objects.filter(report__isnull=False, email__startswith='a'))
logging.info('users with reports (no duplicates)')
logging.info(User.objects.exclude(report__isnull=True).filter(email__startswith='a'))
logging.info('users with reports (no duplicates, simpler SQL)')
report_user_ids = Report.objects.values('user_id')
logging.info(User.objects.filter(id__in=report_user_ids, email__startswith='a'))
logging.info('Done.')
def setup():
db_file = NAME + '.db'
with open(db_file, 'w'):
pass # wipe the database
settings.configure(
DEBUG=True,
DATABASES={
DEFAULT_DB_ALIAS: {
'ENGINE': 'django.db.backends.sqlite3',
'NAME': db_file}},
LOGGING={'version': 1,
'disable_existing_loggers': False,
'formatters': {
'debug': {
'format': '%(asctime)s[%(levelname)s]'
'%(name)s.%(funcName)s(): %(message)s',
'datefmt': '%Y-%m-%d %H:%M:%S'}},
'handlers': {
'console': {
'level': 'DEBUG',
'class': 'logging.StreamHandler',
'formatter': 'debug'}},
'root': {
'handlers': ['console'],
'level': 'INFO'},
'loggers': {
"django.db": {"level": "DEBUG"}}})
app_config = AppConfig(NAME, sys.modules['__main__'])
apps.populate([app_config])
django.setup()
original_new_func = ModelBase.__new__
# noinspection PyDecorator
@staticmethod
def patched_new(cls, name, bases, attrs):
if 'Meta' not in attrs:
class Meta:
app_label = NAME
attrs['Meta'] = Meta
return original_new_func(cls, name, bases, attrs)
ModelBase.__new__ = patched_new
def syncdb(model):
""" Standard syncdb expects models to be in reliable locations.
Based on https://github.com/django/django/blob/1.9.3
/django/core/management/commands/migrate.py#L285
"""
connection = connections[DEFAULT_DB_ALIAS]
with connection.schema_editor() as editor:
editor.create_model(model)
main()
Jeśli umieścisz że do pliku Python i uruchomić go, powinieneś zobaczyć coś takiego:
2017-10-06 09:56:22[DEBUG]django.db.backends.execute(): (0.000) PRAGMA foreign_keys; args=None
2017-10-06 09:56:22[DEBUG]django.db.backends.execute(): (0.000) PRAGMA foreign_keys = 0; args=None
2017-10-06 09:56:22[DEBUG]django.db.backends.execute(): (0.000) BEGIN; args=None
2017-10-06 09:56:22[DEBUG]django.db.backends.schema.execute(): CREATE TABLE "udjango_user" ("id" integer NOT NULL PRIMARY KEY AUTOINCREMENT, "email" varchar(254) NOT NULL); (params None)
2017-10-06 09:56:22[DEBUG]django.db.backends.execute(): (0.000) CREATE TABLE "udjango_user" ("id" integer NOT NULL PRIMARY KEY AUTOINCREMENT, "email" varchar(254) NOT NULL); args=None
2017-10-06 09:56:22[DEBUG]django.db.backends.execute(): (0.000) PRAGMA foreign_keys = 0; args=None
2017-10-06 09:56:22[DEBUG]django.db.backends.execute(): (0.000) PRAGMA foreign_keys; args=None
2017-10-06 09:56:22[DEBUG]django.db.backends.execute(): (0.000) PRAGMA foreign_keys = 0; args=None
2017-10-06 09:56:22[DEBUG]django.db.backends.execute(): (0.000) BEGIN; args=None
2017-10-06 09:56:22[DEBUG]django.db.backends.schema.execute(): CREATE TABLE "udjango_report" ("id" integer NOT NULL PRIMARY KEY AUTOINCREMENT, "user_id" integer NOT NULL REFERENCES "udjango_user" ("id")); (params None)
2017-10-06 09:56:22[DEBUG]django.db.backends.execute(): (0.000) CREATE TABLE "udjango_report" ("id" integer NOT NULL PRIMARY KEY AUTOINCREMENT, "user_id" integer NOT NULL REFERENCES "udjango_user" ("id")); args=None
2017-10-06 09:56:22[DEBUG]django.db.backends.schema.execute(): CREATE INDEX "udjango_report_e8701ad4" ON "udjango_report" ("user_id"); (params [])
2017-10-06 09:56:22[DEBUG]django.db.backends.execute(): (0.000) CREATE INDEX "udjango_report_e8701ad4" ON "udjango_report" ("user_id"); args=[]
2017-10-06 09:56:22[DEBUG]django.db.backends.execute(): (0.000) PRAGMA foreign_keys = 0; args=None
2017-10-06 09:56:22[DEBUG]django.db.backends.execute(): (0.000) BEGIN; args=None
2017-10-06 09:56:22[DEBUG]django.db.backends.execute(): (0.000) INSERT INTO "udjango_user" ("email") VALUES ('[email protected]'); args=['[email protected]']
2017-10-06 09:56:22[DEBUG]django.db.backends.execute(): (0.000) BEGIN; args=None
2017-10-06 09:56:22[DEBUG]django.db.backends.execute(): (0.000) INSERT INTO "udjango_user" ("email") VALUES ('[email protected]'); args=['[email protected]']
2017-10-06 09:56:22[DEBUG]django.db.backends.execute(): (0.000) BEGIN; args=None
2017-10-06 09:56:22[DEBUG]django.db.backends.execute(): (0.000) INSERT INTO "udjango_user" ("email") VALUES ('[email protected]'); args=['[email protected]']
2017-10-06 09:56:22[DEBUG]django.db.backends.execute(): (0.000) BEGIN; args=None
2017-10-06 09:56:22[DEBUG]django.db.backends.execute(): (0.000) INSERT INTO "udjango_user" ("email") VALUES ('[email protected]'); args=['[email protected]']
2017-10-06 09:56:22[DEBUG]django.db.backends.execute(): (0.000) BEGIN; args=None
2017-10-06 09:56:22[DEBUG]django.db.backends.execute(): (0.000) INSERT INTO "udjango_report" ("user_id") VALUES (1); args=[1]
2017-10-06 09:56:22[DEBUG]django.db.backends.execute(): (0.000) BEGIN; args=None
2017-10-06 09:56:22[DEBUG]django.db.backends.execute(): (0.000) INSERT INTO "udjango_report" ("user_id") VALUES (3); args=[3]
2017-10-06 09:56:22[DEBUG]django.db.backends.execute(): (0.000) BEGIN; args=None
2017-10-06 09:56:22[DEBUG]django.db.backends.execute(): (0.000) INSERT INTO "udjango_report" ("user_id") VALUES (3); args=[3]
2017-10-06 09:56:22[INFO]root.main(): users without reports
2017-10-06 09:56:22[DEBUG]django.db.backends.execute(): (0.000) SELECT "udjango_user"."id", "udjango_user"."email" FROM "udjango_user" LEFT OUTER JOIN "udjango_report" ON ("udjango_user"."id" = "udjango_report"."user_id") WHERE ("udjango_report"."id" IS NULL AND "udjango_user"."email" LIKE 'a%' ESCAPE '\') LIMIT 21; args=(u'a%',)
2017-10-06 09:56:22[INFO]root.main(): [User(u'[email protected]')]
2017-10-06 09:56:22[INFO]root.main(): users with reports (allows duplicates)
2017-10-06 09:56:22[DEBUG]django.db.backends.execute(): (0.000) SELECT "udjango_user"."id", "udjango_user"."email" FROM "udjango_user" INNER JOIN "udjango_report" ON ("udjango_user"."id" = "udjango_report"."user_id") WHERE ("udjango_report"."id" IS NOT NULL AND "udjango_user"."email" LIKE 'a%' ESCAPE '\') LIMIT 21; args=(u'a%',)
2017-10-06 09:56:22[INFO]root.main(): [User(u'[email protected]'), User(u'[email protected]'), User(u'[email protected]')]
2017-10-06 09:56:22[INFO]root.main(): users with reports (no duplicates)
2017-10-06 09:56:22[DEBUG]django.db.backends.execute(): (0.000) SELECT "udjango_user"."id", "udjango_user"."email" FROM "udjango_user" WHERE (NOT ("udjango_user"."id" IN (SELECT U0."id" AS Col1 FROM "udjango_user" U0 LEFT OUTER JOIN "udjango_report" U1 ON (U0."id" = U1."user_id") WHERE U1."id" IS NULL)) AND "udjango_user"."email" LIKE 'a%' ESCAPE '\') LIMIT 21; args=(u'a%',)
2017-10-06 09:56:22[INFO]root.main(): [User(u'[email protected]'), User(u'[email protected]')]
2017-10-06 09:56:22[INFO]root.main(): users with reports (no duplicates, simpler SQL)
2017-10-06 09:56:22[DEBUG]django.db.backends.execute(): (0.000) SELECT "udjango_user"."id", "udjango_user"."email" FROM "udjango_user" WHERE ("udjango_user"."email" LIKE 'a%' ESCAPE '\' AND "udjango_user"."id" IN (SELECT U0."user_id" FROM "udjango_report" U0)) LIMIT 21; args=(u'a%',)
2017-10-06 09:56:22[INFO]root.main(): [User(u'[email protected]'), User(u'[email protected]')]
2017-10-06 09:56:22[INFO]root.main(): Done.
Możesz zobaczyć, że zapytanie końcowe wykorzystuje wszystkie połączenia wewnętrzne.
To jest OK, ale generuje 'ZEWNĘTRZNE JOINNE' z' raportem 'w przypadku zarówno '__isnull = True' i' __isnull = False'. W przypadku pytania o użytkowników z raportami może być ono mniej efektywne niż "INNER JOIN". Znalazłem brzydki hack w tym przypadku: 'User.objects.filter (report__id__gt = 0) .distinct()'. Zakłada się, że identyfikatory są> 0, co nie musi być przypadkiem. Czy jest jakiś lepszy sposób na wymuszenie wewnętrznego sprzężenia? –