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"""
27. Many-to-many relationships between the same two tables
In this example, A Person can have many friends, who are also people. Friendship is a
symmetrical relationship - if I am your friend, you are my friend.
A person can also have many idols - but while I may idolize you, you may not think
the same of me. 'Idols' is an example of a non-symmetrical m2m field. Only recursive
m2m fields may be non-symmetrical, and they are symmetrical by default.
This test validates that the m2m table will create a mangled name for the m2m table if
there will be a clash, and tests that symmetry is preserved where appropriate.
"""
from django.db import models
class Person(models.Model):
name = models.CharField(maxlength=20)
friends = models.ManyToManyField('self')
idols = models.ManyToManyField('self', symmetrical=False, related_name='stalkers')
def __str__(self):
return self.name
__test__ = {'API_TESTS':"""
>>> a = Person(name='Anne')
>>> a.save()
>>> b = Person(name='Bill')
>>> b.save()
>>> c = Person(name='Chuck')
>>> c.save()
>>> d = Person(name='David')
>>> d.save()
# Add some friends in the direction of field definition
# Anne is friends with Bill and Chuck
>>> a.friends.add(b,c)
# David is friends with Anne and Chuck - add in reverse direction
>>> d.friends.add(a,c)
# Who is friends with Anne?
>>> a.friends.all()
[<Person: Bill>, <Person: Chuck>, <Person: David>]
# Who is friends with Bill?
>>> b.friends.all()
[<Person: Anne>]
# Who is friends with Chuck?
>>> c.friends.all()
[<Person: Anne>, <Person: David>]
# Who is friends with David?
>>> d.friends.all()
[<Person: Anne>, <Person: Chuck>]
# Bill is already friends with Anne - add Anne again, but in the reverse direction
>>> b.friends.add(a)
# Who is friends with Anne?
>>> a.friends.all()
[<Person: Bill>, <Person: Chuck>, <Person: David>]
# Who is friends with Bill?
>>> b.friends.all()
[<Person: Anne>]
# Remove Anne from Bill's friends
>>> b.friends.remove(a)
# Who is friends with Anne?
>>> a.friends.all()
[<Person: Chuck>, <Person: David>]
# Who is friends with Bill?
>>> b.friends.all()
[]
# Clear Anne's group of friends
>>> a.friends.clear()
# Who is friends with Anne?
>>> a.friends.all()
[]
# Reverse relationships should also be gone
# Who is friends with Chuck?
>>> c.friends.all()
[<Person: David>]
# Who is friends with David?
>>> d.friends.all()
[<Person: Chuck>]
# Add some idols in the direction of field definition
# Anne idolizes Bill and Chuck
>>> a.idols.add(b,c)
# Bill idolizes Anne right back
>>> b.idols.add(a)
# David is idolized by Anne and Chuck - add in reverse direction
>>> d.stalkers.add(a,c)
# Who are Anne's idols?
>>> a.idols.all()
[<Person: Bill>, <Person: Chuck>, <Person: David>]
# Who is stalking Anne?
>>> a.stalkers.all()
[<Person: Bill>]
# Who are Bill's idols?
>>> b.idols.all()
[<Person: Anne>]
# Who is stalking Bill?
>>> b.stalkers.all()
[<Person: Anne>]
# Who are Chuck's idols?
>>> c.idols.all()
[<Person: David>]
# Who is stalking Chuck?
>>> c.stalkers.all()
[<Person: Anne>]
# Who are David's idols?
>>> d.idols.all()
[]
# Who is stalking David
>>> d.stalkers.all()
[<Person: Anne>, <Person: Chuck>]
# Bill is already being stalked by Anne - add Anne again, but in the reverse direction
>>> b.stalkers.add(a)
# Who are Anne's idols?
>>> a.idols.all()
[<Person: Bill>, <Person: Chuck>, <Person: David>]
# Who is stalking Anne?
[<Person: Bill>]
# Who are Bill's idols
>>> b.idols.all()
[<Person: Anne>]
# Who is stalking Bill?
>>> b.stalkers.all()
[<Person: Anne>]
# Remove Anne from Bill's list of stalkers
>>> b.stalkers.remove(a)
# Who are Anne's idols?
>>> a.idols.all()
[<Person: Chuck>, <Person: David>]
# Who is stalking Anne?
>>> a.stalkers.all()
[<Person: Bill>]
# Who are Bill's idols?
>>> b.idols.all()
[<Person: Anne>]
# Who is stalking Bill?
>>> b.stalkers.all()
[]
# Clear Anne's group of idols
>>> a.idols.clear()
# Who are Anne's idols
>>> a.idols.all()
[]
# Reverse relationships should also be gone
# Who is stalking Chuck?
>>> c.stalkers.all()
[]
# Who is friends with David?
>>> d.stalkers.all()
[<Person: Chuck>]
"""}
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