Trying to change IntegerProperty to FloatProperty of existing AppEngine DataStore. Getting error Indexed value must be at most 1500 bytes - python-2.7

Question

BEFORE :
class Person(ndb.Model):
name = ndb.StringProperty()
age = ndb.StringProperty()
other_details = ndb.StructuredProperty(OtherDetails, 'othrdtl')
class OtherDetails(ndb.Model):
success = ndb.StringProperty()
qr_code = ndb.TextProperty()
AFTER:
class Person(ndb.Expando):
pass
rows_to_be_updated = []
for person in Person.all():
person.age = int(person.age)
rows_to_be_updated.append(person)
if len(rows_to_be_updated)>0:
ndb.put_multi_async(rows_to_be_updated)
#"When the above line is executed i am getting error"
Very AFTER:
class Person(db.Model):
name = db.StringProperty()
age = db.IntegerProperty()
other_details = ndb.StructuredProperty(OtherDetails, 'othrdtl')
As per the datastore document, the TextProperty is unindexed by default. What is the reason for the error? I have tried making explicit Indexed=False (ndb.TextProperty(indexed= False)) but didn't work.

Answer 1

Instead of trying to go through an expando model, you might consider using a different name in your database than in your model.
E.g. after
class Person(ndb.Model):
name = ndb.StringProperty()
string_age = ndb.StringProperty('age')
age = ndb.IntegerProperty('int_age')
other_details = ndb.StructuredProperty(OtherDetails, 'othrdtl')
Then you could use a hook to ensure that Person.age is always set, e.g.
class Person(ndb.Model):
#classmethod
def _post_get_hook(cls, key, future):
p = future.get_result()
if p and not p.age:
p.age = int(p.string_age)