1 """ |
|
2 4. Many-to-one relationships |
|
3 |
|
4 To define a many-to-one relationship, use ``ForeignKey()`` . |
|
5 """ |
|
6 |
|
7 from django.db import models |
|
8 |
|
9 class Reporter(models.Model): |
|
10 first_name = models.CharField(maxlength=30) |
|
11 last_name = models.CharField(maxlength=30) |
|
12 email = models.EmailField() |
|
13 |
|
14 def __str__(self): |
|
15 return "%s %s" % (self.first_name, self.last_name) |
|
16 |
|
17 class Article(models.Model): |
|
18 headline = models.CharField(maxlength=100) |
|
19 pub_date = models.DateField() |
|
20 reporter = models.ForeignKey(Reporter) |
|
21 |
|
22 def __str__(self): |
|
23 return self.headline |
|
24 |
|
25 class Meta: |
|
26 ordering = ('headline',) |
|
27 |
|
28 __test__ = {'API_TESTS':""" |
|
29 # Create a few Reporters. |
|
30 >>> r = Reporter(first_name='John', last_name='Smith', email='john@example.com') |
|
31 >>> r.save() |
|
32 |
|
33 >>> r2 = Reporter(first_name='Paul', last_name='Jones', email='paul@example.com') |
|
34 >>> r2.save() |
|
35 |
|
36 # Create an Article. |
|
37 >>> from datetime import datetime |
|
38 >>> a = Article(id=None, headline="This is a test", pub_date=datetime(2005, 7, 27), reporter=r) |
|
39 >>> a.save() |
|
40 |
|
41 >>> a.reporter.id |
|
42 1 |
|
43 |
|
44 >>> a.reporter |
|
45 <Reporter: John Smith> |
|
46 |
|
47 # Article objects have access to their related Reporter objects. |
|
48 >>> r = a.reporter |
|
49 >>> r.first_name, r.last_name |
|
50 ('John', 'Smith') |
|
51 |
|
52 # Create an Article via the Reporter object. |
|
53 >>> new_article = r.article_set.create(headline="John's second story", pub_date=datetime(2005, 7, 29)) |
|
54 >>> new_article |
|
55 <Article: John's second story> |
|
56 >>> new_article.reporter.id |
|
57 1 |
|
58 |
|
59 # Create a new article, and add it to the article set. |
|
60 >>> new_article2 = Article(headline="Paul's story", pub_date=datetime(2006, 1, 17)) |
|
61 >>> r.article_set.add(new_article2) |
|
62 >>> new_article2.reporter.id |
|
63 1 |
|
64 >>> r.article_set.all() |
|
65 [<Article: John's second story>, <Article: Paul's story>, <Article: This is a test>] |
|
66 |
|
67 # Add the same article to a different article set - check that it moves. |
|
68 >>> r2.article_set.add(new_article2) |
|
69 >>> new_article2.reporter.id |
|
70 2 |
|
71 >>> r.article_set.all() |
|
72 [<Article: John's second story>, <Article: This is a test>] |
|
73 >>> r2.article_set.all() |
|
74 [<Article: Paul's story>] |
|
75 |
|
76 # Assign the article to the reporter directly using the descriptor |
|
77 >>> new_article2.reporter = r |
|
78 >>> new_article2.save() |
|
79 >>> new_article2.reporter |
|
80 <Reporter: John Smith> |
|
81 >>> new_article2.reporter.id |
|
82 1 |
|
83 >>> r.article_set.all() |
|
84 [<Article: John's second story>, <Article: Paul's story>, <Article: This is a test>] |
|
85 >>> r2.article_set.all() |
|
86 [] |
|
87 |
|
88 # Set the article back again using set descriptor. |
|
89 >>> r2.article_set = [new_article, new_article2] |
|
90 >>> r.article_set.all() |
|
91 [<Article: This is a test>] |
|
92 >>> r2.article_set.all() |
|
93 [<Article: John's second story>, <Article: Paul's story>] |
|
94 |
|
95 # Funny case - assignment notation can only go so far; because the |
|
96 # ForeignKey cannot be null, existing members of the set must remain |
|
97 >>> r.article_set = [new_article] |
|
98 >>> r.article_set.all() |
|
99 [<Article: John's second story>, <Article: This is a test>] |
|
100 >>> r2.article_set.all() |
|
101 [<Article: Paul's story>] |
|
102 |
|
103 # Reporter cannot be null - there should not be a clear or remove method |
|
104 >>> hasattr(r2.article_set, 'remove') |
|
105 False |
|
106 >>> hasattr(r2.article_set, 'clear') |
|
107 False |
|
108 |
|
109 # Reporter objects have access to their related Article objects. |
|
110 >>> r.article_set.all() |
|
111 [<Article: John's second story>, <Article: This is a test>] |
|
112 |
|
113 >>> r.article_set.filter(headline__startswith='This') |
|
114 [<Article: This is a test>] |
|
115 |
|
116 >>> r.article_set.count() |
|
117 2 |
|
118 |
|
119 >>> r2.article_set.count() |
|
120 1 |
|
121 |
|
122 # Get articles by id |
|
123 >>> Article.objects.filter(id__exact=1) |
|
124 [<Article: This is a test>] |
|
125 >>> Article.objects.filter(pk=1) |
|
126 [<Article: This is a test>] |
|
127 |
|
128 # Query on an article property |
|
129 >>> Article.objects.filter(headline__startswith='This') |
|
130 [<Article: This is a test>] |
|
131 |
|
132 # The API automatically follows relationships as far as you need. |
|
133 # Use double underscores to separate relationships. |
|
134 # This works as many levels deep as you want. There's no limit. |
|
135 # Find all Articles for any Reporter whose first name is "John". |
|
136 >>> Article.objects.filter(reporter__first_name__exact='John') |
|
137 [<Article: John's second story>, <Article: This is a test>] |
|
138 |
|
139 # Check that implied __exact also works |
|
140 >>> Article.objects.filter(reporter__first_name='John') |
|
141 [<Article: John's second story>, <Article: This is a test>] |
|
142 |
|
143 # Query twice over the related field. |
|
144 >>> Article.objects.filter(reporter__first_name__exact='John', reporter__last_name__exact='Smith') |
|
145 [<Article: John's second story>, <Article: This is a test>] |
|
146 |
|
147 # The underlying query only makes one join when a related table is referenced twice. |
|
148 >>> query = Article.objects.filter(reporter__first_name__exact='John', reporter__last_name__exact='Smith') |
|
149 >>> null, sql, null = query._get_sql_clause() |
|
150 >>> sql.count('INNER JOIN') |
|
151 1 |
|
152 |
|
153 # The automatically joined table has a predictable name. |
|
154 >>> Article.objects.filter(reporter__first_name__exact='John').extra(where=["many_to_one_article__reporter.last_name='Smith'"]) |
|
155 [<Article: John's second story>, <Article: This is a test>] |
|
156 |
|
157 # Find all Articles for the Reporter whose ID is 1. |
|
158 # Use direct ID check, pk check, and object comparison |
|
159 >>> Article.objects.filter(reporter__id__exact=1) |
|
160 [<Article: John's second story>, <Article: This is a test>] |
|
161 >>> Article.objects.filter(reporter__pk=1) |
|
162 [<Article: John's second story>, <Article: This is a test>] |
|
163 >>> Article.objects.filter(reporter=1) |
|
164 [<Article: John's second story>, <Article: This is a test>] |
|
165 >>> Article.objects.filter(reporter=r) |
|
166 [<Article: John's second story>, <Article: This is a test>] |
|
167 |
|
168 >>> Article.objects.filter(reporter__in=[1,2]).distinct() |
|
169 [<Article: John's second story>, <Article: Paul's story>, <Article: This is a test>] |
|
170 >>> Article.objects.filter(reporter__in=[r,r2]).distinct() |
|
171 [<Article: John's second story>, <Article: Paul's story>, <Article: This is a test>] |
|
172 |
|
173 # You need two underscores between "reporter" and "id" -- not one. |
|
174 >>> Article.objects.filter(reporter_id__exact=1) |
|
175 Traceback (most recent call last): |
|
176 ... |
|
177 TypeError: Cannot resolve keyword 'reporter_id' into field |
|
178 |
|
179 # You need to specify a comparison clause |
|
180 >>> Article.objects.filter(reporter_id=1) |
|
181 Traceback (most recent call last): |
|
182 ... |
|
183 TypeError: Cannot resolve keyword 'reporter_id' into field |
|
184 |
|
185 # You can also instantiate an Article by passing |
|
186 # the Reporter's ID instead of a Reporter object. |
|
187 >>> a3 = Article(id=None, headline="This is a test", pub_date=datetime(2005, 7, 27), reporter_id=r.id) |
|
188 >>> a3.save() |
|
189 >>> a3.reporter.id |
|
190 1 |
|
191 >>> a3.reporter |
|
192 <Reporter: John Smith> |
|
193 |
|
194 # Similarly, the reporter ID can be a string. |
|
195 >>> a4 = Article(id=None, headline="This is a test", pub_date=datetime(2005, 7, 27), reporter_id="1") |
|
196 >>> a4.save() |
|
197 >>> a4.reporter |
|
198 <Reporter: John Smith> |
|
199 |
|
200 # Reporters can be queried |
|
201 >>> Reporter.objects.filter(id__exact=1) |
|
202 [<Reporter: John Smith>] |
|
203 >>> Reporter.objects.filter(pk=1) |
|
204 [<Reporter: John Smith>] |
|
205 >>> Reporter.objects.filter(first_name__startswith='John') |
|
206 [<Reporter: John Smith>] |
|
207 |
|
208 # Reporters can query in opposite direction of ForeignKey definition |
|
209 >>> Reporter.objects.filter(article__id__exact=1) |
|
210 [<Reporter: John Smith>] |
|
211 >>> Reporter.objects.filter(article__pk=1) |
|
212 [<Reporter: John Smith>] |
|
213 >>> Reporter.objects.filter(article=1) |
|
214 [<Reporter: John Smith>] |
|
215 >>> Reporter.objects.filter(article=a) |
|
216 [<Reporter: John Smith>] |
|
217 |
|
218 >>> Reporter.objects.filter(article__in=[1,4]).distinct() |
|
219 [<Reporter: John Smith>] |
|
220 >>> Reporter.objects.filter(article__in=[1,a3]).distinct() |
|
221 [<Reporter: John Smith>] |
|
222 >>> Reporter.objects.filter(article__in=[a,a3]).distinct() |
|
223 [<Reporter: John Smith>] |
|
224 |
|
225 >>> Reporter.objects.filter(article__headline__startswith='This') |
|
226 [<Reporter: John Smith>, <Reporter: John Smith>, <Reporter: John Smith>] |
|
227 >>> Reporter.objects.filter(article__headline__startswith='This').distinct() |
|
228 [<Reporter: John Smith>] |
|
229 |
|
230 # Counting in the opposite direction works in conjunction with distinct() |
|
231 >>> Reporter.objects.filter(article__headline__startswith='This').count() |
|
232 3 |
|
233 >>> Reporter.objects.filter(article__headline__startswith='This').distinct().count() |
|
234 1 |
|
235 |
|
236 # Queries can go round in circles. |
|
237 >>> Reporter.objects.filter(article__reporter__first_name__startswith='John') |
|
238 [<Reporter: John Smith>, <Reporter: John Smith>, <Reporter: John Smith>, <Reporter: John Smith>] |
|
239 >>> Reporter.objects.filter(article__reporter__first_name__startswith='John').distinct() |
|
240 [<Reporter: John Smith>] |
|
241 >>> Reporter.objects.filter(article__reporter__exact=r).distinct() |
|
242 [<Reporter: John Smith>] |
|
243 |
|
244 # Check that implied __exact also works |
|
245 >>> Reporter.objects.filter(article__reporter=r).distinct() |
|
246 [<Reporter: John Smith>] |
|
247 |
|
248 # If you delete a reporter, his articles will be deleted. |
|
249 >>> Article.objects.all() |
|
250 [<Article: John's second story>, <Article: Paul's story>, <Article: This is a test>, <Article: This is a test>, <Article: This is a test>] |
|
251 >>> Reporter.objects.order_by('first_name') |
|
252 [<Reporter: John Smith>, <Reporter: Paul Jones>] |
|
253 >>> r2.delete() |
|
254 >>> Article.objects.all() |
|
255 [<Article: John's second story>, <Article: This is a test>, <Article: This is a test>, <Article: This is a test>] |
|
256 >>> Reporter.objects.order_by('first_name') |
|
257 [<Reporter: John Smith>] |
|
258 |
|
259 # Deletes using a join in the query |
|
260 >>> Reporter.objects.filter(article__headline__startswith='This').delete() |
|
261 >>> Reporter.objects.all() |
|
262 [] |
|
263 >>> Article.objects.all() |
|
264 [] |
|
265 |
|
266 """} |
|