Question

I have this two models: Tutorial and Chapter. Chapters have a key reference to the tutorial they belong. Now I’m trying to list all the chapter that belong to a specific Tutorial but I can’t get the query to work:

class TutView(FuHandler):
    def get(self):
        tutKey = self.request.get('tut_key')
        tut = db.Key.from_path('Tutorial', tutKey)
        chaps = db.GqlQuery("SELECT * FROM Chapter " +
                            "WHERE __key__ = KEY('Tutorial', :1)", tut)
        self.render('tutView.html', chaps=chaps)

When running I get this error:

BadArgumentError: Expected an integer id or string name as argument 2; 
received datastore_types.Key.from_path(u'Tutorial', u'<bound method 
Tutorial.key of <main.Tutorial object at 0x00.............

---

Chapter model:

class Chapter(db.Model):
    tutorial = db.ReferenceProperty(Tutorial, collection_name='chapters')
    title = db.StringProperty(required=True)
    content = db.TextProperty(required=True)

Tutorial model:

class Tutorial(db.Model):
    title = db.StringProperty(required=True)
    presentation = db.TextProperty(required=True)

---

update:
i managed to get no errors but i get no results (so, probably it’s wrong):

chaps = db.GqlQuery("SELECT * FROM Chapter " + 
                    "WHERE __key__ = KEY('tutorial', :1)", str(tutKey))

update2:
The problem might be on the way i store or retrieve the tutKey. I’m getting the key with the URL… and and that’s probably not working… but i don’t know other way

Answer 1

The KEY() GQL function is used to create Keys based on two parameters: The Entity, and the name/id.
If you look at your code, you will see that you are passing it a db.Key object as a parameter.
Hence, the error message:

Expected an integer id or string name as argument 2; 
received datastore_types.Key.from_path(u'Tutorial', ...)

Also, you need to test against the tutorial property of the Chapter entity, and not against its own __key__.

I do not work with GQL, I use the Query objects instead. You provide them with the db.Key object directly, so I assume this should work:

chaps = db.GqlQuery("SELECT * FROM Chapter " +
                        "WHERE tutorial = :1", tut)

If it doesn’t, you can always try:

chaps = db.GqlQuery("SELECT * FROM Chapter " +
                        "WHERE tutorial = KEY('Tutorial', :1)", tut.id() or tut.name())