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