擅长:python、mysql、java
<p>你显然不能这么做。正如<a href="http://code.google.com/appengine/docs/python/datastore/queries.html#Restrictions_on_Queries" rel="nofollow">documentation</a>所述:</p>
<blockquote>
<p>It is not possible to query for entities that are missing a given property.</p>
</blockquote>
<p>相反,请为<code>is_assessed</code>创建一个默认为False的属性,并对其进行查询。在</p>