On 06/14/2016 11:28 AM, Ken Linehan wrote:
Hello,
I'm working with a class inheritance structure which can be illustrated
by this example:
|
class Entity(object):
def __init__(self,
entity_type=EntityTypeEntity,
id=None):
self.entity_type = entity_type
self.id = id
class Person(Entity):
def __init__(self,
entity_class=None,
entity_type=EntityTypePerson,
id=None,
name_first=None,
name_last=None,
name_middle=None,
name_prefix=None,
name_suffix=None):
super(Person, self).__init__(entity_type,
id)
self.entity_class = entity_class
self.name_first = name_first
self.name_last = name_last
self.name_middle = name_middle
self.name_prefix = name_prefix
self.name_suffix = name_suffix
class SupporterPerson(Person):
def __init__(self,
entity_class=EntityClassSupporterPerson,
entity_type=EntityTypePerson,
id=None,
name_first=None,
name_last=None,
name_middle=None,
name_prefix=None,
name_suffix=None,
relationship=None):
super(SupporterPerson, self).__init__(entity_class,
entity_type,
id,
name_first,
name_last,
name_middle,
name_prefix,
name_suffix)
self.relationship = relationship
|
My current mappings look like this:
|
# Mappers
self.entity_table_mapper = mapper(
Entity,
self.entities_table,
polymorphic_on=self.entities_table.c.entity_type,
polymorphic_identity=EntityTypeEntity,
with_polymorphic='*',
properties={
'entity_type': self.entities_table.c.entity_type,
'id': self.entities_table.c.id,
}
)
self.persons_table_mapper = mapper(
Person,
self.persons_table,
polymorphic_on=self.persons_table.c.entity_class,
polymorphic_identity=EntityTypePerson,
with_polymorphic='*',
inherits=Entity,
)
self.supporter_persons_table_mapper = mapper(
SupporterPerson,
self.supporter_persons_table,
polymorphic_identity=EntityClassSupporterPerson,
with_polymorphic='*',
inherits=Person,
)
|
I am able to instantiate a SupporterPerson() and successfully store all
attributes correctly in their respective tables. So the mapping seems to
work well. However...
what's likely happening is that you're attempting to use two levels of
polymorphic_on which isn't supported right now. a load of Entity will
only consider those classes it can identify via entity_type.
There's a fairly elaborate proof of concept for this feature at
https://bitbucket.org/zzzeek/sqlalchemy/issues/2555/cascading-polymorphic-ons
, I've just re-reviewed it and it should still work.
In the broader context of my application, a query to load Causes() (
sketched out below ) will eagerload a list of that causes supporters.
When supporters are eagerloaded, the supporter is reliably loaded to
the level of Person() however the attributes specific to
SupporterPerson() are not loaded. In other words, the attributes
specific to the youngest child in my class inheritance, structure are
NOT loaded by the eagerload.
|
class Cause(object):
def __init__(self,
id=None
supporters=None):
self.id = id
self.supporters = [] if supporters is None else None
|
So my question is, Is there a problem with my mapping? Or is this depth
of inheritance not supported by the eagerload? Or perhaps there is
something else I'm missing altogether ( unrelated to the eagerload ) ?
Any advice or assistance would be greatly appreciated. Sorry if I'm
missing something that is already clearly stated in the documentation.
Best,
Ken
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