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copied!<p>I have a model with a reference property, eg:</p> <pre><code>class Data(db.Model): x = db.IntegerProperty() class Details(db.Model): data = db.ReferenceProperty(reference_class = Data) </code></pre> <p>The data reference can be None.</p> <p>I want to fetch all Details entities which have valid data, ie for which the reference property is not None.</p> <p>The following works:</p> <pre><code>Details.all().filter('data !=', None).fetch(1000) </code></pre> <p>However, according to the <a href="http://code.google.com/appengine/docs/python/datastore/queriesandindexes.html#Introducing_Queries" rel="nofollow noreferrer">documentation on queries</a>, a <code>!=</code> query will actually perform two queries, which seems unnecessary in this case. Is <code>!=</code> optimised to only perform one query when used with None?</p> <p>Alternatively, <a href="http://groups.google.com/group/google-appengine-python/browse_thread/thread/18f3a9a4c4b690c8" rel="nofollow noreferrer">this post</a> mentions that NULL always sorts before valid values. Therefore the following also appears to work:</p> <pre><code>Details.all().filter('data >', None).fetch(1000) </code></pre> <p>Although this would only do one query, using <code>></code> instead of <code>!=</code> makes the intent of what it is doing less obvious.</p> <p>As a third option, I could add an extra field to the model:</p> <pre><code>class Details(db.Model): data = db.ReferenceProperty(reference_class = Data) has_data = db.BooleanProperty() </code></pre> <p>As long as I keep has_data synchronised with data, I could do:</p> <pre><code>Details.all().filter('has_data =', True).fetch(1000) </code></pre> <p>Which way would be best?</p> <p>Thanks.</p>

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