"""

40. 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(maxlength=50)

    def __str__(self):

        return self.name

class Kingdom(models.Model):

    name = models.CharField(maxlength=50)

    domain = models.ForeignKey(Domain)

    def __str__(self):

        return self.name

class Phylum(models.Model):

    name = models.CharField(maxlength=50)

    kingdom = models.ForeignKey(Kingdom)

    def __str__(self):

        return self.name

class Klass(models.Model):

    name = models.CharField(maxlength=50)

    phylum = models.ForeignKey(Phylum)

    def __str__(self):

        return self.name

class Order(models.Model):

    name = models.CharField(maxlength=50)

    klass = models.ForeignKey(Klass)

    def __str__(self):

        return self.name

class Family(models.Model):

    name = models.CharField(maxlength=50)

    order = models.ForeignKey(Order)

    def __str__(self):

        return self.name

class Genus(models.Model):

    name = models.CharField(maxlength=50)

    family = models.ForeignKey(Family)

    def __str__(self):

        return self.name

class Species(models.Model):

    name = models.CharField(maxlength=50)

    genus = models.ForeignKey(Genus)

    def __str__(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().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 few query 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

# Reset DEBUG to where we found it.

>>> settings.DEBUG = False

"""}