"""

4. Many-to-one relationships

To define a many-to-one relationship, use ``ForeignKey()`` .

"""

from django.db import models

class Reporter(models.Model):

    first_name = models.CharField(maxlength=30)

    last_name = models.CharField(maxlength=30)

    email = models.EmailField()

    def __str__(self):

        return "%s %s" % (self.first_name, self.last_name)

class Article(models.Model):

    headline = models.CharField(maxlength=100)

    pub_date = models.DateField()

    reporter = models.ForeignKey(Reporter)

    def __str__(self):

        return self.headline

    class Meta:

        ordering = ('headline',)

__test__ = {'API_TESTS':"""

# Create a few Reporters.

>>> r = Reporter(first_name='John', last_name='Smith', email='john@example.com')

>>> r.save()

>>> r2 = Reporter(first_name='Paul', last_name='Jones', email='paul@example.com')

>>> r2.save()

# Create an Article.

>>> from datetime import datetime

>>> a = Article(id=None, headline="This is a test", pub_date=datetime(2005, 7, 27), reporter=r)

>>> a.save()

>>> a.reporter.id

1

>>> a.reporter

<Reporter: John Smith>

# Article objects have access to their related Reporter objects.

>>> r = a.reporter

>>> r.first_name, r.last_name

('John', 'Smith')

# Create an Article via the Reporter object.

>>> new_article = r.article_set.create(headline="John's second story", pub_date=datetime(2005, 7, 29))

>>> new_article

<Article: John's second story>

>>> new_article.reporter.id

1

# Create a new article, and add it to the article set.

>>> new_article2 = Article(headline="Paul's story", pub_date=datetime(2006, 1, 17))

>>> r.article_set.add(new_article2)

>>> new_article2.reporter.id

1

>>> r.article_set.all()

[<Article: John's second story>, <Article: Paul's story>, <Article: This is a test>]

# Add the same article to a different article set - check that it moves.

>>> r2.article_set.add(new_article2)

>>> new_article2.reporter.id

2

>>> r.article_set.all()

[<Article: John's second story>, <Article: This is a test>]

>>> r2.article_set.all()

[<Article: Paul's story>]

# Assign the article to the reporter directly using the descriptor

>>> new_article2.reporter = r

>>> new_article2.save()

>>> new_article2.reporter

<Reporter: John Smith>

>>> new_article2.reporter.id

1

>>> r.article_set.all()

[<Article: John's second story>, <Article: Paul's story>, <Article: This is a test>]

>>> r2.article_set.all()

[]

# Set the article back again using set descriptor.

>>> r2.article_set = [new_article, new_article2]

>>> r.article_set.all()

[<Article: This is a test>]

>>> r2.article_set.all()

[<Article: John's second story>, <Article: Paul's story>]

# Funny case - assignment notation can only go so far; because the

# ForeignKey cannot be null, existing members of the set must remain

>>> r.article_set = [new_article]

>>> r.article_set.all()

[<Article: John's second story>, <Article: This is a test>]

>>> r2.article_set.all()

[<Article: Paul's story>]

# Reporter cannot be null - there should not be a clear or remove method

>>> hasattr(r2.article_set, 'remove')

False

>>> hasattr(r2.article_set, 'clear')

False

# Reporter objects have access to their related Article objects.

>>> r.article_set.all()

[<Article: John's second story>, <Article: This is a test>]

>>> r.article_set.filter(headline__startswith='This')

[<Article: This is a test>]

>>> r.article_set.count()

2

>>> r2.article_set.count()

1

# Get articles by id

>>> Article.objects.filter(id__exact=1)

[<Article: This is a test>]

>>> Article.objects.filter(pk=1)

[<Article: This is a test>]

# Query on an article property

>>> Article.objects.filter(headline__startswith='This')

[<Article: This is a test>]

# The API automatically follows relationships as far as you need.

# Use double underscores to separate relationships.

# This works as many levels deep as you want. There's no limit.

# Find all Articles for any Reporter whose first name is "John".

>>> Article.objects.filter(reporter__first_name__exact='John')

[<Article: John's second story>, <Article: This is a test>]

# Check that implied __exact also works

>>> Article.objects.filter(reporter__first_name='John')

[<Article: John's second story>, <Article: This is a test>]

# Query twice over the related field.

>>> Article.objects.filter(reporter__first_name__exact='John', reporter__last_name__exact='Smith')

[<Article: John's second story>, <Article: This is a test>]

# The underlying query only makes one join when a related table is referenced twice.

>>> query = Article.objects.filter(reporter__first_name__exact='John', reporter__last_name__exact='Smith')

>>> null, sql, null = query._get_sql_clause()

>>> sql.count('INNER JOIN')

1

# The automatically joined table has a predictable name.

>>> Article.objects.filter(reporter__first_name__exact='John').extra(where=["many_to_one_article__reporter.last_name='Smith'"])

[<Article: John's second story>, <Article: This is a test>]

# Find all Articles for the Reporter whose ID is 1.

# Use direct ID check, pk check, and object comparison 

>>> Article.objects.filter(reporter__id__exact=1)

[<Article: John's second story>, <Article: This is a test>]

>>> Article.objects.filter(reporter__pk=1)

[<Article: John's second story>, <Article: This is a test>]

>>> Article.objects.filter(reporter=1)

[<Article: John's second story>, <Article: This is a test>]

>>> Article.objects.filter(reporter=r)

[<Article: John's second story>, <Article: This is a test>]

>>> Article.objects.filter(reporter__in=[1,2]).distinct()

[<Article: John's second story>, <Article: Paul's story>, <Article: This is a test>]

>>> Article.objects.filter(reporter__in=[r,r2]).distinct()

[<Article: John's second story>, <Article: Paul's story>, <Article: This is a test>]

# You need two underscores between "reporter" and "id" -- not one.

>>> Article.objects.filter(reporter_id__exact=1)

Traceback (most recent call last):

    ...

TypeError: Cannot resolve keyword 'reporter_id' into field

# You need to specify a comparison clause

>>> Article.objects.filter(reporter_id=1)

Traceback (most recent call last):

    ...

TypeError: Cannot resolve keyword 'reporter_id' into field

# You can also instantiate an Article by passing

# the Reporter's ID instead of a Reporter object.

>>> a3 = Article(id=None, headline="This is a test", pub_date=datetime(2005, 7, 27), reporter_id=r.id)

>>> a3.save()

>>> a3.reporter.id

1

>>> a3.reporter

<Reporter: John Smith>

# Similarly, the reporter ID can be a string.

>>> a4 = Article(id=None, headline="This is a test", pub_date=datetime(2005, 7, 27), reporter_id="1")

>>> a4.save()

>>> a4.reporter

<Reporter: John Smith>

# Reporters can be queried

>>> Reporter.objects.filter(id__exact=1)

[<Reporter: John Smith>]

>>> Reporter.objects.filter(pk=1)

[<Reporter: John Smith>]

>>> Reporter.objects.filter(first_name__startswith='John')

[<Reporter: John Smith>]

# Reporters can query in opposite direction of ForeignKey definition

>>> Reporter.objects.filter(article__id__exact=1)

[<Reporter: John Smith>]

>>> Reporter.objects.filter(article__pk=1)

[<Reporter: John Smith>]

>>> Reporter.objects.filter(article=1)

[<Reporter: John Smith>]

>>> Reporter.objects.filter(article=a)

[<Reporter: John Smith>]

>>> Reporter.objects.filter(article__in=[1,4]).distinct()

[<Reporter: John Smith>]

>>> Reporter.objects.filter(article__in=[1,a3]).distinct()

[<Reporter: John Smith>]

>>> Reporter.objects.filter(article__in=[a,a3]).distinct()

[<Reporter: John Smith>]

>>> Reporter.objects.filter(article__headline__startswith='This')

[<Reporter: John Smith>, <Reporter: John Smith>, <Reporter: John Smith>]

>>> Reporter.objects.filter(article__headline__startswith='This').distinct()

[<Reporter: John Smith>]

# Counting in the opposite direction works in conjunction with distinct()

>>> Reporter.objects.filter(article__headline__startswith='This').count()

3

>>> Reporter.objects.filter(article__headline__startswith='This').distinct().count()

1

# Queries can go round in circles.

>>> Reporter.objects.filter(article__reporter__first_name__startswith='John')

[<Reporter: John Smith>, <Reporter: John Smith>, <Reporter: John Smith>, <Reporter: John Smith>]

>>> Reporter.objects.filter(article__reporter__first_name__startswith='John').distinct()

[<Reporter: John Smith>]

>>> Reporter.objects.filter(article__reporter__exact=r).distinct()

[<Reporter: John Smith>]

# Check that implied __exact also works

>>> Reporter.objects.filter(article__reporter=r).distinct()

[<Reporter: John Smith>]

# If you delete a reporter, his articles will be deleted.

>>> Article.objects.all()

[<Article: John's second story>, <Article: Paul's story>, <Article: This is a test>, <Article: This is a test>, <Article: This is a test>]

>>> Reporter.objects.order_by('first_name')

[<Reporter: John Smith>, <Reporter: Paul Jones>]

>>> r2.delete()

>>> Article.objects.all()

[<Article: John's second story>, <Article: This is a test>, <Article: This is a test>, <Article: This is a test>]

>>> Reporter.objects.order_by('first_name')

[<Reporter: John Smith>]

# Deletes using a join in the query

>>> Reporter.objects.filter(article__headline__startswith='This').delete()

>>> Reporter.objects.all()

[]

>>> Article.objects.all()

[]

"""}