the "non polymorphic" search is against the Person mapper; it
recieves id "1" and looks in the identity map for (Person, (1,)) and
locates the existing object immediately. For id 2, it also looks in
the map for (Person, (2,)), and finds nothing; it must issue a query
which returns the fact that id 2 is of type "employee", creates the
proper identity key of (Employee, (2,)), and returns the value from
the identity map.
On Jul 15, 2007, at 7:56 AM, Yves-Eric wrote:
>
> Hi all again,
>
>
> Trying to deploy polymorphic inheritance, I am now hit by what may be
> another bug: it seems like getting polymorphic objects may be 100
> times slower than regular ones.
>
> I reproduce the problem in the copy-pastable script below, using a
> single table polymorphic inheritance scenario. On my machine, the
> output of this script gives me:
>
> The non-polymorphic loop took 0.082 seconds
> The polymorphic loop took 7.916 seconds
> The polymorphic loop was 96 times slower
>
> I know that there may be *some* overhead in using polymorphism, but 96
> times slower sounds way too much, so I am suspecting some form of bug.
>
> Is this a known issue? Is there a work around?
>
> Thank you for your help!
>
>
> ### BEGIN: polymorphic_inheritance_slowness_test.py ###
> from sqlalchemy import *
>
> db = create_engine('sqlite://', echo=False)
> __meta__ = BoundMetaData(db)
>
> person_table = Table("persons", __meta__,
> Column("id", Integer, primary_key=True),
> Column("ptype", String(80)), # Polymorphic ID field
> Column("name", String(80)),
> )
>
> class Person(object):
> def __init__(self, name):
> self.name = name
>
> class Employee(Person): pass
>
> __meta__.create_all()
>
> person_mapper = mapper(Person, person_table,
> polymorphic_on=person_table.c.ptype)
> mapper(Employee, person_table, inherits=person_mapper,
> polymorphic_identity='EMPLOYEE')
>
>
> person_insert = person_table.insert()
> # Alice is just a Person (non-polymorphic)
> person_insert.execute(id=1, ptype=None, name='alice')
> # Bob is an Employee (polymorphic)
> person_insert.execute(id=2, ptype='EMPLOYEE', name='bob')
>
> session = create_session()
> query = session.query(Person)
>
> # Now timing loops getting our 2 objects:
> from time import time
> start1 = time()
> # Non-polymorphic get loop
> for i in range(5000):
> dummy = query.get(1)
>
> time1 = time() - start1
>
> start2 = time()
> # Polymorphic get loop
> for i in range(5000):
> dummy = query.get(2)
>
> time2 = time() - start2
>
> print """The non-polymorphic loop took %0.3f seconds
> The polymorphic loop took %0.3f seconds
> The polymorphic loop was %i times slower""" % (time1, time2, time2/
> time1)
>
> ### END ###
>
>
> >
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