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299 lines
11 KiB
299 lines
11 KiB
""" |
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4. Many-to-one relationships |
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To define a many-to-one relationship, use ``ForeignKey()``. |
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""" |
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from django.db import models |
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class Reporter(models.Model): |
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first_name = models.CharField(max_length=30) |
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last_name = models.CharField(max_length=30) |
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email = models.EmailField() |
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def __unicode__(self): |
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return u"%s %s" % (self.first_name, self.last_name) |
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class Article(models.Model): |
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headline = models.CharField(max_length=100) |
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pub_date = models.DateField() |
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reporter = models.ForeignKey(Reporter) |
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def __unicode__(self): |
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return self.headline |
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class Meta: |
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ordering = ('headline',) |
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__test__ = {'API_TESTS':""" |
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# Create a few Reporters. |
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>>> r = Reporter(first_name='John', last_name='Smith', email='john@example.com') |
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>>> r.save() |
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>>> r2 = Reporter(first_name='Paul', last_name='Jones', email='paul@example.com') |
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>>> r2.save() |
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# Create an Article. |
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>>> from datetime import datetime |
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>>> a = Article(id=None, headline="This is a test", pub_date=datetime(2005, 7, 27), reporter=r) |
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>>> a.save() |
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>>> a.reporter.id |
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1 |
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>>> a.reporter |
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<Reporter: John Smith> |
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# Article objects have access to their related Reporter objects. |
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>>> r = a.reporter |
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# These are strings instead of unicode strings because that's what was used in |
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# the creation of this reporter (and we haven't refreshed the data from the |
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# database, which always returns unicode strings). |
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>>> r.first_name, r.last_name |
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('John', 'Smith') |
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# Create an Article via the Reporter object. |
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>>> new_article = r.article_set.create(headline="John's second story", pub_date=datetime(2005, 7, 29)) |
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>>> new_article |
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<Article: John's second story> |
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>>> new_article.reporter.id |
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1 |
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# Create a new article, and add it to the article set. |
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>>> new_article2 = Article(headline="Paul's story", pub_date=datetime(2006, 1, 17)) |
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>>> r.article_set.add(new_article2) |
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>>> new_article2.reporter.id |
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1 |
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>>> r.article_set.all() |
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[<Article: John's second story>, <Article: Paul's story>, <Article: This is a test>] |
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# Add the same article to a different article set - check that it moves. |
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>>> r2.article_set.add(new_article2) |
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>>> new_article2.reporter.id |
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2 |
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>>> r.article_set.all() |
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[<Article: John's second story>, <Article: This is a test>] |
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>>> r2.article_set.all() |
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[<Article: Paul's story>] |
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# Assign the article to the reporter directly using the descriptor |
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>>> new_article2.reporter = r |
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>>> new_article2.save() |
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>>> new_article2.reporter |
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<Reporter: John Smith> |
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>>> new_article2.reporter.id |
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1 |
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>>> r.article_set.all() |
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[<Article: John's second story>, <Article: Paul's story>, <Article: This is a test>] |
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>>> r2.article_set.all() |
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[] |
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# Set the article back again using set descriptor. |
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>>> r2.article_set = [new_article, new_article2] |
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>>> r.article_set.all() |
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[<Article: This is a test>] |
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>>> r2.article_set.all() |
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[<Article: John's second story>, <Article: Paul's story>] |
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# Funny case - assignment notation can only go so far; because the |
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# ForeignKey cannot be null, existing members of the set must remain |
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>>> r.article_set = [new_article] |
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>>> r.article_set.all() |
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[<Article: John's second story>, <Article: This is a test>] |
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>>> r2.article_set.all() |
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[<Article: Paul's story>] |
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# Reporter cannot be null - there should not be a clear or remove method |
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>>> hasattr(r2.article_set, 'remove') |
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False |
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>>> hasattr(r2.article_set, 'clear') |
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False |
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# Reporter objects have access to their related Article objects. |
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>>> r.article_set.all() |
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[<Article: John's second story>, <Article: This is a test>] |
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>>> r.article_set.filter(headline__startswith='This') |
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[<Article: This is a test>] |
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>>> r.article_set.count() |
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2 |
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>>> r2.article_set.count() |
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1 |
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# Get articles by id |
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>>> Article.objects.filter(id__exact=1) |
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[<Article: This is a test>] |
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>>> Article.objects.filter(pk=1) |
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[<Article: This is a test>] |
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# Query on an article property |
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>>> Article.objects.filter(headline__startswith='This') |
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[<Article: This is a test>] |
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# The API automatically follows relationships as far as you need. |
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# Use double underscores to separate relationships. |
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# This works as many levels deep as you want. There's no limit. |
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# Find all Articles for any Reporter whose first name is "John". |
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>>> Article.objects.filter(reporter__first_name__exact='John') |
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[<Article: John's second story>, <Article: This is a test>] |
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# Check that implied __exact also works |
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>>> Article.objects.filter(reporter__first_name='John') |
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[<Article: John's second story>, <Article: This is a test>] |
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# Query twice over the related field. |
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>>> Article.objects.filter(reporter__first_name__exact='John', reporter__last_name__exact='Smith') |
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[<Article: John's second story>, <Article: This is a test>] |
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# The underlying query only makes one join when a related table is referenced twice. |
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>>> queryset = Article.objects.filter(reporter__first_name__exact='John', reporter__last_name__exact='Smith') |
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>>> sql = queryset.query.as_sql()[0] |
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>>> sql.count('INNER JOIN') |
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1 |
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# The automatically joined table has a predictable name. |
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>>> Article.objects.filter(reporter__first_name__exact='John').extra(where=["many_to_one_reporter.last_name='Smith'"]) |
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[<Article: John's second story>, <Article: This is a test>] |
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# And should work fine with the unicode that comes out of |
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# forms.Form.cleaned_data |
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>>> Article.objects.filter(reporter__first_name__exact='John').extra(where=["many_to_one_reporter.last_name='%s'" % u'Smith']) |
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[<Article: John's second story>, <Article: This is a test>] |
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# Find all Articles for the Reporter whose ID is 1. |
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# Use direct ID check, pk check, and object comparison |
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>>> Article.objects.filter(reporter__id__exact=1) |
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[<Article: John's second story>, <Article: This is a test>] |
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>>> Article.objects.filter(reporter__pk=1) |
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[<Article: John's second story>, <Article: This is a test>] |
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>>> Article.objects.filter(reporter=1) |
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[<Article: John's second story>, <Article: This is a test>] |
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>>> Article.objects.filter(reporter=r) |
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[<Article: John's second story>, <Article: This is a test>] |
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>>> Article.objects.filter(reporter__in=[1,2]).distinct() |
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[<Article: John's second story>, <Article: Paul's story>, <Article: This is a test>] |
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>>> Article.objects.filter(reporter__in=[r,r2]).distinct() |
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[<Article: John's second story>, <Article: Paul's story>, <Article: This is a test>] |
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# You can also use a queryset instead of a literal list of instances. |
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# The queryset must be reduced to a list of values using values(), |
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# then converted into a query |
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>>> Article.objects.filter(reporter__in=Reporter.objects.filter(first_name='John').values('pk').query).distinct() |
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[<Article: John's second story>, <Article: This is a test>] |
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# You need two underscores between "reporter" and "id" -- not one. |
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>>> Article.objects.filter(reporter_id__exact=1) |
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Traceback (most recent call last): |
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... |
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FieldError: Cannot resolve keyword 'reporter_id' into field. Choices are: headline, id, pub_date, reporter |
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# You need to specify a comparison clause |
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>>> Article.objects.filter(reporter_id=1) |
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Traceback (most recent call last): |
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... |
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FieldError: Cannot resolve keyword 'reporter_id' into field. Choices are: headline, id, pub_date, reporter |
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# You can also instantiate an Article by passing |
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# the Reporter's ID instead of a Reporter object. |
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>>> a3 = Article(id=None, headline="This is a test", pub_date=datetime(2005, 7, 27), reporter_id=r.id) |
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>>> a3.save() |
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>>> a3.reporter.id |
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1 |
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>>> a3.reporter |
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<Reporter: John Smith> |
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# Similarly, the reporter ID can be a string. |
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>>> a4 = Article(id=None, headline="This is a test", pub_date=datetime(2005, 7, 27), reporter_id="1") |
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>>> a4.save() |
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>>> a4.reporter |
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<Reporter: John Smith> |
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# Reporters can be queried |
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>>> Reporter.objects.filter(id__exact=1) |
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[<Reporter: John Smith>] |
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>>> Reporter.objects.filter(pk=1) |
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[<Reporter: John Smith>] |
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>>> Reporter.objects.filter(first_name__startswith='John') |
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[<Reporter: John Smith>] |
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# Reporters can query in opposite direction of ForeignKey definition |
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>>> Reporter.objects.filter(article__id__exact=1) |
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[<Reporter: John Smith>] |
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>>> Reporter.objects.filter(article__pk=1) |
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[<Reporter: John Smith>] |
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>>> Reporter.objects.filter(article=1) |
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[<Reporter: John Smith>] |
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>>> Reporter.objects.filter(article=a) |
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[<Reporter: John Smith>] |
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>>> Reporter.objects.filter(article__in=[1,4]).distinct() |
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[<Reporter: John Smith>] |
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>>> Reporter.objects.filter(article__in=[1,a3]).distinct() |
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[<Reporter: John Smith>] |
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>>> Reporter.objects.filter(article__in=[a,a3]).distinct() |
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[<Reporter: John Smith>] |
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>>> Reporter.objects.filter(article__headline__startswith='This') |
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[<Reporter: John Smith>, <Reporter: John Smith>, <Reporter: John Smith>] |
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>>> Reporter.objects.filter(article__headline__startswith='This').distinct() |
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[<Reporter: John Smith>] |
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# Counting in the opposite direction works in conjunction with distinct() |
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>>> Reporter.objects.filter(article__headline__startswith='This').count() |
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3 |
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>>> Reporter.objects.filter(article__headline__startswith='This').distinct().count() |
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1 |
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# Queries can go round in circles. |
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>>> Reporter.objects.filter(article__reporter__first_name__startswith='John') |
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[<Reporter: John Smith>, <Reporter: John Smith>, <Reporter: John Smith>, <Reporter: John Smith>] |
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>>> Reporter.objects.filter(article__reporter__first_name__startswith='John').distinct() |
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[<Reporter: John Smith>] |
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>>> Reporter.objects.filter(article__reporter__exact=r).distinct() |
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[<Reporter: John Smith>] |
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# Check that implied __exact also works. |
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>>> Reporter.objects.filter(article__reporter=r).distinct() |
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[<Reporter: John Smith>] |
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# It's possible to use values() calls across many-to-one relations. (Note, too, that we clear the ordering here so as not to drag the 'headline' field into the columns being used to determine uniqueness.) |
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>>> d = {'reporter__first_name': u'John', 'reporter__last_name': u'Smith'} |
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>>> list(Article.objects.filter(reporter=r).distinct().order_by().values('reporter__first_name', 'reporter__last_name')) == [d] |
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True |
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# If you delete a reporter, his articles will be deleted. |
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>>> Article.objects.all() |
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[<Article: John's second story>, <Article: Paul's story>, <Article: This is a test>, <Article: This is a test>, <Article: This is a test>] |
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>>> Reporter.objects.order_by('first_name') |
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[<Reporter: John Smith>, <Reporter: Paul Jones>] |
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>>> r2.delete() |
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>>> Article.objects.all() |
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[<Article: John's second story>, <Article: This is a test>, <Article: This is a test>, <Article: This is a test>] |
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>>> Reporter.objects.order_by('first_name') |
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[<Reporter: John Smith>] |
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# You can delete using a JOIN in the query. |
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>>> Reporter.objects.filter(article__headline__startswith='This').delete() |
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>>> Reporter.objects.all() |
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[] |
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>>> Article.objects.all() |
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[] |
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# Check that Article.objects.select_related().dates() works properly when |
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# there are multiple Articles with the same date but different foreign-key |
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# objects (Reporters). |
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>>> r1 = Reporter.objects.create(first_name='Mike', last_name='Royko', email='royko@suntimes.com') |
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>>> r2 = Reporter.objects.create(first_name='John', last_name='Kass', email='jkass@tribune.com') |
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>>> a1 = Article.objects.create(headline='First', pub_date=datetime(1980, 4, 23), reporter=r1) |
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>>> a2 = Article.objects.create(headline='Second', pub_date=datetime(1980, 4, 23), reporter=r2) |
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>>> Article.objects.select_related().dates('pub_date', 'day') |
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[datetime.datetime(1980, 4, 23, 0, 0)] |
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>>> Article.objects.select_related().dates('pub_date', 'month') |
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[datetime.datetime(1980, 4, 1, 0, 0)] |
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>>> Article.objects.select_related().dates('pub_date', 'year') |
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[datetime.datetime(1980, 1, 1, 0, 0)] |
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"""}
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