How to filter rows with zero errors in a Google database

Question

I have a UnitPattern model that references another UnitPatternSet model

eg.

class UnitPattern(db.Model):
    unit_pattern_set = db.ReferenceProperty(UnitPatternSet)

in my opinion, I want to display all UnitPattern elements with unit_pattern_set parameters as None, but the request is UnitPattern.all (). filter ("unit_pattern_set =", None) returns nothing, although I have only 5 UnitPatterns, of which 2 are 'unit_pattern_set' and 3 do not have

eg.

print 'Total',UnitPattern.all().count()
print 'ref set',UnitPattern.all().filter("unit_pattern_set !=", None).count()
print 'ref not set',UnitPattern.all().filter("unit_pattern_set =", None).count()

outputs:

Total 5
ref set 2
ref not set 0

Should the sum of queries 2 and 3 be equal to query 1?

It seems that the reason is that I added the reference_pattern_set property later, and these UnitPattern objects existed before that, but how can I filter such objects?

Answer 1

docs:

, , . , , , , .

, App Engine , , (None). , , , (, None) , .

3 , unit_pattern_set ( ), , .

Google App Engine . 150 ( , Google )

, , UnitPattern ( , , , ):

patterns = UnitPattern.all()
for pattern in patterns:
  if not pattern.unit_pattern_set:
    pattern.unit_pattern_set = None
    pattern.put()

: , , , . , , - URL-, , - , , , . deferred.defer , - ​​ , DeadlineExceededError , , .