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"""
8. get_latest_by
Models can have a ``get_latest_by`` attribute, which should be set to the name
of a ``DateField`` or ``DateTimeField``. If ``get_latest_by`` exists, the
model's manager will get a ``latest()`` method, which will return the latest
object in the database according to that field. "Latest" means "having the date
farthest into the future."
"""
from django.db import models
class Article(models.Model):
headline = models.CharField(max_length=100)
pub_date = models.DateField()
expire_date = models.DateField()
class Meta:
get_latest_by = 'pub_date'
def __unicode__(self):
return self.headline
class Person(models.Model):
name = models.CharField(max_length=30)
birthday = models.DateField()
# Note that this model doesn't have "get_latest_by" set.
def __unicode__(self):
return self.name
__test__ = {'API_TESTS':"""
# Because no Articles exist yet, latest() raises ArticleDoesNotExist.
>>> Article.objects.latest()
Traceback (most recent call last):
...
DoesNotExist: Article matching query does not exist.
# Create a couple of Articles.
>>> from datetime import datetime
>>> a1 = Article(headline='Article 1', pub_date=datetime(2005, 7, 26), expire_date=datetime(2005, 9, 1))
>>> a1.save()
>>> a2 = Article(headline='Article 2', pub_date=datetime(2005, 7, 27), expire_date=datetime(2005, 7, 28))
>>> a2.save()
>>> a3 = Article(headline='Article 3', pub_date=datetime(2005, 7, 27), expire_date=datetime(2005, 8, 27))
>>> a3.save()
>>> a4 = Article(headline='Article 4', pub_date=datetime(2005, 7, 28), expire_date=datetime(2005, 7, 30))
>>> a4.save()
# Get the latest Article.
>>> Article.objects.latest()
<Article: Article 4>
# Get the latest Article that matches certain filters.
>>> Article.objects.filter(pub_date__lt=datetime(2005, 7, 27)).latest()
<Article: Article 1>
# Pass a custom field name to latest() to change the field that's used to
# determine the latest object.
>>> Article.objects.latest('expire_date')
<Article: Article 1>
>>> Article.objects.filter(pub_date__gt=datetime(2005, 7, 26)).latest('expire_date')
<Article: Article 3>
# You can still use latest() with a model that doesn't have "get_latest_by"
# set -- just pass in the field name manually.
>>> p1 = Person(name='Ralph', birthday=datetime(1950, 1, 1))
>>> p1.save()
>>> p2 = Person(name='Stephanie', birthday=datetime(1960, 2, 3))
>>> p2.save()
>>> Person.objects.latest()
Traceback (most recent call last):
...
AssertionError: latest() requires either a field_name parameter or 'get_latest_by' in the model
>>> Person.objects.latest('birthday')
<Person: Stephanie>
"""}
|
