Why doesn't my GQL query return any results in my GAE App?

I have mostly followed a tutorial about how to build a gustbook using GAE and Python. Now I only want to show the entries from a particular day, but the GQL query doesn't return anything (although there are entries from that day):

class Shout(db.Model):  
    message= db.StringProperty(required=True)  
    when = db.DateTimeProperty(auto_now_add=True)  
    who = db.StringProperty()  

class MainHandler(webapp.RequestHandler):  
    def get(self):  
        shouts = db.GqlQuery("SELECT * FROM Shout WHERE when=DATE('2010-11-05')")  
        # Return something without the WHERE clause
        values = {'shouts':shouts}  
        self.response.out.write(template.render('main.开发者_高级运维html',values))  

    def post(self):  
        self.response.out.write("posted")  
        shout = Shout(message=self.request.get("message"),who=self.request.get("who"))  
        shout.put()  

This is my main.html:

<form method="post">
   <input type="text" name="who"></input>
   <input type="text" name="message"></input>
   <input type="submit" value="Send"> </input>  
</form>

{% for shout in shouts  %}
   <div>{{shout.message}} from {{shout.who}} on {{shout.when}}</div>
{% endfor %}

There might be another way around this, but I think that because your when property is a datetime you would be better served with something like this:

shouts = db.GqlQuery("""SELECT * 
                          FROM Shout 
                         WHERE when >= DATE('2010-11-05')
                           AND when < DATE('2010-11-06')""")

Try this:

shouts = db.GqlQuery("SELECT * FROM Shout WHERE when=DATE('2010-11-05')").fetch(5000)

While it is possible to use a Query object as an iterable, it is a better idea to explicitly fetch the rows and not depend on the for in your template to do the work. I suspect that it is not supported in that way.

EDIT: Now that I look more closely at this, I suspect that the problem is that the field you are querying on is a DateTimeProperty, and by using the DATE operator, you are essentially saying that you want 2010-11-05 00:00:00, and there are no records with that exact date and time, so try this instead:

shouts = db.GqlQuery("SELECT * FROM Shout WHERE when >= DATETIME('2010-11-05 00:00:00') and when <= DATETIME('2010-11-05 23:59:59')")