Hi Jordan!
Thanks for the reply. However, I didn't quite catch how the answer is
related to my question. But, maybe I can clarify the question with this
quote: “To be eligible as a query result, an entity must possess a value
(possibly null) for every property named in the query's filters and sort
orders.” [0]
So, you can query None/null values. (Note: this has nothing to do with
missing/unset values.) I'm also using this *a lot*, and never experienced
any issues.
But for lists (with NDB at least), querying with None/null is undefined:
“Querying for a value of None on a repeated property has undefined
behavior; don't do that.” [1]
Is there an explanation for this difference?
I tested this, and NDB does seem to work as I was assuming. But, I have no
idea whether I can trust that behaviour, due to the quote [1]. (If it
really is undefined, as stated.)
My test procedure, very simple:
First I created an entity of
class SomeEntity(ndb.Model):
field_abc = ndb.IntegerProperty()
with field_abc=None.
Then I created another entity of
class SomeEntity(ndb.Model):
field_abc = SparseIntegerProperty(repeated=True)
with field_abc=[1, 2, None].
where
class SparseIntegerProperty(ndb.Property):
def _db_set_value(self, v, unused_p, value):
if isinstance(value, (int, long)):
v.set_int64value(value)
def _db_get_value(self, v, unused_p):
if v.has_int64value():
return int(v.int64value())
(Yes, I've used such a “sparse” property in a significant production
application for many years.)
And the query works as I was expecting:
s~my-project> SomeEntity.query(SomeEntity.field_abc == None).fetch()
[SomeEntity(key=Key('SomeEntity', 3892735977), field_abc=[None]),
SomeEntity(key=Key('SomeEntity', 3896345977), field_abc=[1, 2, None])]
But, to repeat, I don't know whether I can trust this behaviour.
ps. I do not believe this is a “technical support” question.
pps. doesn't this related to ndb.StructuredProperty as well? If a
sub-entity has a field with Null value, and you query by it? Aren't the
sub-entities indexed simply as repeated fields? Thus, you'd query a list by
a None value, in a very concrete fashion. I haven't checked this yet…
-Janne
On Wednesday, November 29, 2017 at 10:50:45 PM UTC+2, Jordan (Cloud
Platform Support) wrote:
>
> It comes down to how the Datastore distinguishes if an Entity property has
> a value or not. If a property has no value (aka it is never set and is
> None) than the Datastore is unable to filter on that specific property
> (since it doesn't have it) and will not return that Entity in a query. This
> is explained in the documentation under "Entities lacking a property
> named in the query are ignored
> <https://cloud.google.com/datastore/docs/concepts/queries#restrictions_on_queries>
> "
>
> The workaround is to assign a default value to a property such a null.
> Once a value is assigned it will then be visible to a filter and can be
> returned in a query.
>
> - Note that Google Groups is for general product discussions and not for
> technical support. If you require further Datastore technical support it is
> recommended to post your full detailed question
> <https://stackoverflow.com/help/how-to-ask> to Stack Overflow
> <https://cloud.google.com/support/docs/stackexchange> using the supported
> Cloud tags.
>
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