Current Django Version: 1.11
Methods that return new QuerySets
Can be chained:
Entry.objects.filter(**kwargs).exclude(**kwargs).order_by(**kwargs)Entry.objects.filter(id__in=[1, 3, 4])
SELECT ... WHERE id IN (1, 3, 4);
inner_qs = Blog.objects.filter(name__contains='Cheddar')
entries = Entry.objects.filter(blog__in=inner_qs)
SELECT ... WHERE blog.id IN (SELECT id FROM ... WHERE NAME LIKE '%Cheddar%')Entry.objects.exclude(pub_date__gt=datetime.date(2005, 1, 3), headline='Hello')
SELECT ... WHERE NOT (pub_date > '2005-1-3' AND headline = 'Hello')
Entry.objects.exclude(pub_date__gt=datetime.date(2005, 1, 3))/
.exclude(headline='Hello')
SELECT ... WHERE NOT pub_date > '2005-1-3' AND NOT headline = 'Hello'>>> from django.db.models import Count
>>> q = Blog.objects.annotate(Count('entry'))
# The name of the first blog
>>> q[0].name
'Blogasaurus'
# The number of entries on the first blog
>>> q[0].entry__count
42
>>> q = Blog.objects.annotate(number_of_entries=Count('entry'))
# The number of entries on the first blog, using the name provided
>>> q[0].number_of_entries
42Entry.objects.filter(pub_date__year=2005).order_by('-pub_date', 'headline')
The result above will be ordered by pub_date descending,
then by headline ascending.
The negative sign in front of "-pub_date" indicates descending order.
Ascending order is implied.
# No Join
Entry.objects.order_by('blog_id')
# Join
Entry.objects.order_by('blog__id')Use the reverse() method to reverse the order in
which a queryset’s elements are returned.
Calling reverse() a second time restores the ordering back to the normal direction.
my_queryset.reverse()[:5]When using distinct() and values() together, be careful when ordering by fields
not in the values() call.
When you specify field names, you must provide an order_by() in the QuerySet,
and the fields in order_by() must start with the fields in distinct(),
in the same order.
Author.objects.distinct()
Entry.objects.order_by('pub_date').distinct('pub_date')
Entry.objects.order_by('blog__name', 'mod_date').distinct('blog__name', 'mod_date')Blog.objects.filter(name__startswith='Beatles').values()
[{'id': 1, 'name': 'Beatles Blog', 'tagline': 'All the latest Beatles news.'}]
Entry.objects.values('blog_id')
[{'blog_id': 1}, ...]
Blog.objects.values('name', 'entry__headline')
[{'name': 'My blog', 'entry__headline': 'An entry'},
{'name': 'My blog', 'entry__headline': 'Another entry'}, ...]Entry.objects.values_list('id', 'headline')
[(1, 'First entry'), ...]
Entry.objects.values_list('id', flat=True).order_by('id')
[1, 2, 3, ...]field should be the name of a DateField of your model.
kind should be either "year", "month" or "day".
Each datetime.date object in the result list is “truncated” to the given type.
* "year" returns a list of all distinct year values for the field.
* "month" returns a list of all distinct year/month values for the field.
* "day" returns a list of all distinct year/month/day values for the field.
Entry.objects.dates('pub_date', 'year')
[datetime.date(2005, 1, 1)]
Entry.objects.dates('pub_date', 'month')
[datetime.date(2005, 2, 1), datetime.date(2005, 3, 1)]
Entry.objects.dates('pub_date', 'day')
[datetime.date(2005, 2, 20), datetime.date(2005, 3, 20)]
Entry.objects.dates('pub_date', 'day', order='DESC')
[datetime.date(2005, 3, 20), datetime.date(2005, 2, 20)]tzinfo defines the time zone to which datetimes are converted prior to truncation.
Indeed, a given datetime has different representations depending on the time zone in use.
This parameter must be a datetime.tzinfo object.
If it’s None, Django uses the current time zone. It has no effect when USE_TZ is False.
This function performs time zone conversions directly in the database.
As a consequence, your database must be able to interpret the value of tzinfo.tzname(None).
This translates into the following requirements:
* SQLite: install pytz — conversions are actually performed in Python.
* PostgreSQL: no requirements (see Time Zones).
* Oracle: no requirements (see Choosing a Time Zone File).
* MySQL: install pytz and load the time zone tables with mysql_tzinfo_to_sql.Calling none() will create a queryset that never returns any objects and
no query will be executed when accessing the results.
A qs.none() queryset is an instance of EmptyQuerySet.
Entry.objects.none()
[]
from django.db.models.query import EmptyQuerySet
isinstance(Entry.objects.none(), EmptyQuerySet)
TrueReturns a copy of the current QuerySet (or QuerySet subclass).
When a QuerySet is evaluated, it typically caches its results.
If the data in the database might have changed since a QuerySet was evaluated,
you can get updated results for the same query by calling all()
on a previously evaluated QuerySet.e = Entry.objects.get(id=5) # Hits the database.
b = e.blog # Hits the database again to get the related Blog object.
# Hits the database.
e = Entry.objects.select_related('blog').get(id=5)
# Doesn't hit the database, because e.blog has been prepopulated
# in the previous query.
b = e.blog
b = Book.objects.select_related('author__hometown').get(id=4)
p = b.author # Doesn't hit the database.
c = p.hometown # Doesn't hit the database.
b = Book.objects.get(id=4) # No select_related() in this example.
p = b.author # Hits the database.
c = p.hometown # Hits the database.