1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
|
"""
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 __unicode__(self):
return self.name
class Kingdom(models.Model):
name = models.CharField(maxlength=50)
domain = models.ForeignKey(Domain)
def __unicode__(self):
return self.name
class Phylum(models.Model):
name = models.CharField(maxlength=50)
kingdom = models.ForeignKey(Kingdom)
def __unicode__(self):
return self.name
class Klass(models.Model):
name = models.CharField(maxlength=50)
phylum = models.ForeignKey(Phylum)
def __unicode__(self):
return self.name
class Order(models.Model):
name = models.CharField(maxlength=50)
klass = models.ForeignKey(Klass)
def __unicode__(self):
return self.name
class Family(models.Model):
name = models.CharField(maxlength=50)
order = models.ForeignKey(Order)
def __unicode__(self):
return self.name
class Genus(models.Model):
name = models.CharField(maxlength=50)
family = models.ForeignKey(Family)
def __unicode__(self):
return self.name
class Species(models.Model):
name = models.CharField(maxlength=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().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
"""}
|
