django1/tests/modeltests/select_related/models.py

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"""
41. Tests for select_related()
``select_related()`` follows all relationships and pre-caches any foreign key
values so that complex trees can be fetched in a single query. However, this
isn't always a good idea, so the ``depth`` argument control how many "levels"
the select-related behavior will traverse.
"""
from django.db import models
# Who remembers high school biology?
class Domain(models.Model):
name = models.CharField(max_length=50)
def __unicode__(self):
return self.name
class Kingdom(models.Model):
name = models.CharField(max_length=50)
domain = models.ForeignKey(Domain)
def __unicode__(self):
return self.name
class Phylum(models.Model):
name = models.CharField(max_length=50)
kingdom = models.ForeignKey(Kingdom)
def __unicode__(self):
return self.name
class Klass(models.Model):
name = models.CharField(max_length=50)
phylum = models.ForeignKey(Phylum)
def __unicode__(self):
return self.name
class Order(models.Model):
name = models.CharField(max_length=50)
klass = models.ForeignKey(Klass)
def __unicode__(self):
return self.name
class Family(models.Model):
name = models.CharField(max_length=50)
order = models.ForeignKey(Order)
def __unicode__(self):
return self.name
class Genus(models.Model):
name = models.CharField(max_length=50)
family = models.ForeignKey(Family)
def __unicode__(self):
return self.name
class Species(models.Model):
name = models.CharField(max_length=50)
genus = models.ForeignKey(Genus)
def __unicode__(self):
return self.name
def create_tree(stringtree):
"""Helper to create a complete tree"""
names = stringtree.split()
models = [Domain, Kingdom, Phylum, Klass, Order, Family, Genus, Species]
assert len(names) == len(models), (names, models)
parent = None
for name, model in zip(names, models):
try:
obj = model.objects.get(name=name)
except model.DoesNotExist:
obj = model(name=name)
if parent:
setattr(obj, parent.__class__.__name__.lower(), parent)
obj.save()
parent = obj
__test__ = {'API_TESTS':"""
# Set up.
# The test runner sets settings.DEBUG to False, but we want to gather queries
# so we'll set it to True here and reset it at the end of the test suite.
>>> from django.conf import settings
>>> settings.DEBUG = True
>>> create_tree("Eukaryota Animalia Anthropoda Insecta Diptera Drosophilidae Drosophila melanogaster")
>>> create_tree("Eukaryota Animalia Chordata Mammalia Primates Hominidae Homo sapiens")
>>> create_tree("Eukaryota Plantae Magnoliophyta Magnoliopsida Fabales Fabaceae Pisum sativum")
>>> create_tree("Eukaryota Fungi Basidiomycota Homobasidiomycatae Agaricales Amanitacae Amanita muscaria")
>>> from django import db
# Normally, accessing FKs doesn't fill in related objects:
>>> db.reset_queries()
>>> fly = Species.objects.get(name="melanogaster")
>>> fly.genus.family.order.klass.phylum.kingdom.domain
<Domain: Eukaryota>
>>> len(db.connection.queries)
8
# However, a select_related() call will fill in those related objects without any extra queries:
>>> db.reset_queries()
>>> person = Species.objects.select_related(depth=10).get(name="sapiens")
>>> person.genus.family.order.klass.phylum.kingdom.domain
<Domain: Eukaryota>
>>> len(db.connection.queries)
1
# select_related() also of course applies to entire lists, not just items.
# Without select_related()
>>> db.reset_queries()
>>> world = Species.objects.all()
>>> [o.genus.family for o in world]
[<Family: Drosophilidae>, <Family: Hominidae>, <Family: Fabaceae>, <Family: Amanitacae>]
>>> len(db.connection.queries)
9
# With select_related():
>>> db.reset_queries()
>>> world = Species.objects.all().select_related()
>>> [o.genus.family for o in world]
[<Family: Drosophilidae>, <Family: Hominidae>, <Family: Fabaceae>, <Family: Amanitacae>]
>>> len(db.connection.queries)
1
# The "depth" argument to select_related() will stop the descent at a particular level:
>>> db.reset_queries()
>>> pea = Species.objects.select_related(depth=1).get(name="sativum")
>>> pea.genus.family.order.klass.phylum.kingdom.domain
<Domain: Eukaryota>
# Notice: one fewer queries than above because of depth=1
>>> len(db.connection.queries)
7
>>> db.reset_queries()
>>> pea = Species.objects.select_related(depth=5).get(name="sativum")
>>> pea.genus.family.order.klass.phylum.kingdom.domain
<Domain: Eukaryota>
>>> len(db.connection.queries)
3
>>> db.reset_queries()
>>> world = Species.objects.all().select_related(depth=2)
>>> [o.genus.family.order for o in world]
[<Order: Diptera>, <Order: Primates>, <Order: Fabales>, <Order: Agaricales>]
>>> len(db.connection.queries)
5
>>> s = Species.objects.all().select_related(depth=1).extra(select={'a': 'select_related_species.id + 10'})[0]
>>> s.id + 10 == s.a
True
# The optional fields passed to select_related() control which related models
# we pull in. This allows for smaller queries and can act as an alternative
# (or, in addition to) the depth parameter.
# In the next two cases, we explicitly say to select the 'genus' and
# 'genus.family' models, leading to the same number of queries as before.
>>> db.reset_queries()
>>> world = Species.objects.select_related('genus__family')
>>> [o.genus.family for o in world]
[<Family: Drosophilidae>, <Family: Hominidae>, <Family: Fabaceae>, <Family: Amanitacae>]
>>> len(db.connection.queries)
1
>>> db.reset_queries()
>>> world = Species.objects.filter(genus__name='Amanita').select_related('genus__family')
>>> [o.genus.family.order for o in world]
[<Order: Agaricales>]
>>> len(db.connection.queries)
2
>>> db.reset_queries()
>>> Species.objects.all().select_related('genus__family__order').order_by('id')[0:1].get().genus.family.order.name
u'Diptera'
>>> len(db.connection.queries)
1
# Specifying both "depth" and fields is an error.
>>> Species.objects.select_related('genus__family__order', depth=4)
Traceback (most recent call last):
...
TypeError: Cannot pass both "depth" and fields to select_related()
# Reset DEBUG to where we found it.
>>> settings.DEBUG = False
"""}