Oh, I forgot to mention: for the test, I commented out this line in
ndb/model.py:
assert b_val is not None, "Cannot wrap None"
I did a bit more testing with queries and everything seemed to work as I
expected. Namely, I tested whether None values would interfere with some
other kind of queries, but I found no such cases.
Also, the missing references from last post:
[0]
https://cloud.google.com/datastore/docs/concepts/queries#restrictions_on_queries
[1] https://cloud.google.com/appengine/docs/standard/python/ndb/queries
-Janne
On Friday, December 1, 2017 at 1:13:49 PM UTC+2, Janne Savukoski wrote:
>
> 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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