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    <p>The error in question is caused when you try to access the <code>Manager</code> of a model through an instance of the model. You have used <em>lower case</em> class names. This makes it hard to say if the error is caused by an instance accessing the <code>Manager</code> or not. Since other scenarios that can cause this error are unknown I am proceeding on the assumption that you have somehow mixed up the <code>topic</code> variable so that you end up pointing to an instance of the <code>topic</code> model instead of the class. </p> <p>This line is the culprit: </p> <pre><code>forum.topic_count = topic.objects.filter(forum = forum).count() # ^^^^^ </code></pre> <p>You have to use:</p> <pre><code>forum.topic_count = Topic.objects.filter(forum = forum).count() # ^^^^^ # Model, not instance. </code></pre> <p>What is going wrong? <code>objects</code> is a <code>Manager</code> available at the class level, not to the instances. See the <a href="http://docs.djangoproject.com/en/dev/topics/db/queries/#retrieving-objects" rel="noreferrer">documentation for retrieving objects</a> for details. Money quote:</p> <blockquote> <p><code>Managers</code> are accessible <strong><em>only</em></strong> via model classes, rather than from model instances, to enforce a separation between "table-level" operations and "record-level" operations.</p> </blockquote> <p>(Emphasis added)</p> <p><strong>Update</strong></p> <p>See the comments from @Daniel below. It is a good idea (nay, you MUST :P) to use title case for class names. For instance <code>Topic</code> instead of <code>topic</code>. Your class names cause some confusion whether you are referring to an instance or a class. Since the <code>Manager isn't accessible via &lt;model&gt; instances</code> is very specific I am able to offer a solution.The error may not be so self evident always. </p>
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    1. USManoj Govindan
    1. USManoj Govindan
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    1. COHowever, `topic` does appear to be the actual model class, and not an instance according to the code he provided.
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      1. USDaniel DiPaolo
    2. CO@Daniel: true. And yet the error `Manager isn't accessible via Foo instances` is only possible when you try to access a `Manager` using an instance. See the source code: http://code.djangoproject.com/svn/django/trunk/django/db/models/manager.py
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    3. COIndeed, perhaps another reason (other than "it's best practice") not to use lowercase letters for class names :) It would appear he's potentially using `topic` as a local instance variable and blowing away the reference to the class.
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