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PODifferent results on query changing Q object order
 

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  1. PODifferent results on query changing Q object order
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    <p>I have a problem when making a queryset using <code>Q</code> objects. I'm getting different results depending on how i order some <code>Q</code> conditions. I will simplify my models a little so as to describe my problem in a clean way.</p> <pre><code>class D(models.Model): one_attr = models.BooleanField() s_attr = models.ManyToManyField(S, through='DRelatedToS') d_to_p = models.ForeignKey(P) class S(models.Model): other_attr = models.BooleanField() s_to_p = models.ForeignKey(P) class DRelatedToS(models.Model): to_s = models.ForeignKey(S) to_d = models.ForeignKey(D) date = models.DateField() class P(models.Model): the_last_attr = models.PositiveIntegerField() </code></pre> <p>Summary of the relations:</p> <blockquote> <pre><code>D &lt;-- DRelatedToS --&gt; S --&gt; P | ^ | | --------&gt;-------&gt;------&gt;----^ </code></pre> </blockquote> <p>With these models and relations, i get two different results depending on how i arrange Q conditions: <strong>First query, that gives one result</strong></p> <pre><code>D.objects.filter( Q(one_attr=True, s_attr__s_to_p__the_last_attr=5) | Q(one_attr=False, d_to_p__the_last_attr=10) ) </code></pre> <p><strong>Second query, giving another result, different from first query</strong></p> <pre><code>D.objects.filter( Q(one_attr=False, d_to_p__the_last_attr=10) | Q(one_attr=True, s_attr__s_to_p__the_last_attr=5) ) </code></pre> <p>My question is: why is this happening? Is there any problem on how i am doing my query? </p> <p>When i watch the SQL statements derived from these queries, i get two different statements: one that make a <code>LEFT OUTER JOIN</code> and a lot of <code>INNER JOIN</code>s and the second that makes all <code>INNER JOIN</code>s. The one that actually return what i want is the one that makes a <code>LEFT OUTER JOIN</code>. This make me feel that all my queries can return bad results depending on how i arrange its conditions. Is this a bug or i am doing anything (or everything) wrong?</p>
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    1. COSimplifying your models is a [Good Thing™](http://sscce.org/)
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