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