Re: [Sqlalchemy-tickets] [sqlalchemy] #2526: can we get subclass mappers to self-collect?

[sqlalchemy <mi...@zz...>]

#2526: can we get subclass mappers to self-collect?
------------------------------+-------------------------------
      Reporter:  zzzeek       |      Owner:  zzzeek
          Type:  enhancement  |     Status:  new
      Priority:  medium       |  Milestone:  0.8.0
     Component:  orm          |   Severity:  major - 1-3 hours
    Resolution:               |   Keywords:
Progress State:  in queue     |
------------------------------+-------------------------------
Description changed by zzzeek:

Old description:

> so far no luck, would need to scan through references to figure this out:
>
> {{{
> #!diff
> diff -r 8b5adc1e004e lib/sqlalchemy/ext/declarative.py
> --- a/lib/sqlalchemy/ext/declarative.py Mon Jun 25 16:42:39 2012 -0400
> +++ b/lib/sqlalchemy/ext/declarative.py Tue Jun 26 12:58:56 2012 -0400
> @@ -1036,7 +1036,7 @@
>  from sqlalchemy.sql import util as sql_util, expression
>  from sqlalchemy import event
>  from sqlalchemy.orm.util import polymorphic_union, _mapper_or_none
> -
> +import weakref
>
>  __all__ = 'declarative_base', 'synonym_for', \
>              'comparable_using', 'instrument_declarative'
> @@ -1718,7 +1718,7 @@
>          lcl_metadata.bind = bind
>
>      if class_registry is None:
> -        class_registry = {}
> +        class_registry = weakref.WeakValueDictionary()
>
>      bases = not isinstance(cls, tuple) and (cls,) or cls
>      class_dict = dict(_decl_class_registry=class_registry,
> diff -r 8b5adc1e004e lib/sqlalchemy/orm/mapper.py
> --- a/lib/sqlalchemy/orm/mapper.py      Mon Jun 25 16:42:39 2012 -0400
> +++ b/lib/sqlalchemy/orm/mapper.py      Tue Jun 26 12:58:56 2012 -0400
> @@ -166,7 +166,7 @@
>          # names with Mappers that will be used to construct object
> instances
>          # upon a select operation.
>          if _polymorphic_map is None:
> -            self.polymorphic_map = {}
> +            self.polymorphic_map = weakref.WeakValueDictionary()
>          else:
>              self.polymorphic_map = _polymorphic_map
>
> @@ -432,7 +432,8 @@
>          being present."""
>
>          # a set of all mappers which inherit from this one.
> -        self._inheriting_mappers = set()
> +        # TODO: WeakSet is only in 2.7, would need compat
> +        self._inheriting_mappers = weakref.WeakSet()
>
>          if self.inherits:
>              if isinstance(self.inherits, type):
> }}}
>
> {{{
> #!python
> from sqlalchemy import *
> from sqlalchemy.orm import *
> from sqlalchemy.ext.declarative import declarative_base
>
> Base= declarative_base()
>
> class Root(Base):
>     __tablename__ = 'root'
>     id = Column(Integer, primary_key=True)
>     type = Column(String)
>     __mapper_args__ = {
>         'polymorphic_on':type,
>         'polymorphic_identity':'root'
>     }
>
> assert not Root.__mapper__._inheriting_mappers
>
> class Sub(Root):
>     __tablename__ = 'sub'
>     metadata = MetaData()
>     id = Column(Integer, ForeignKey(Root.id), primary_key=True)
>     __mapper_args__ = {
>         'polymorphic_identity':'sub'
>     }
>
> e = create_engine("sqlite://")
> Base.metadata.create_all(e)
> Sub.metadata.create_all(e)
>
> s = Session(e)
> s.add_all([Sub(), Sub(), Root()])
> s.commit()
>
> print s.query(Root).all()
>
> s.close()
> del s
> Sub.__mapper__.__dict__.clear() #dispatch = None
> Sub.__mapper__ = None
>
> del Sub
>
> import gc
> gc.collect()
> print Root.__subclasses__()
> #import pdb
> #pdb.set_trace()
> assert not Root.__mapper__._inheriting_mappers
> }}}

New description:

 would need a lot of weak references for this to work automatically,
 particularly the memoizations somehow, which would add some real
 performance overhead:

 {{{
 #!diff
 diff -r 8b5adc1e004e lib/sqlalchemy/ext/declarative.py
 --- a/lib/sqlalchemy/ext/declarative.py Mon Jun 25 16:42:39 2012 -0400
 +++ b/lib/sqlalchemy/ext/declarative.py Tue Jun 26 12:58:56 2012 -0400
 @@ -1036,7 +1036,7 @@
  from sqlalchemy.sql import util as sql_util, expression
  from sqlalchemy import event
  from sqlalchemy.orm.util import polymorphic_union, _mapper_or_none
 -
 +import weakref

  __all__ = 'declarative_base', 'synonym_for', \
              'comparable_using', 'instrument_declarative'
 @@ -1718,7 +1718,7 @@
          lcl_metadata.bind = bind

      if class_registry is None:
 -        class_registry = {}
 +        class_registry = weakref.WeakValueDictionary()

      bases = not isinstance(cls, tuple) and (cls,) or cls
      class_dict = dict(_decl_class_registry=class_registry,
 diff -r 8b5adc1e004e lib/sqlalchemy/orm/mapper.py
 --- a/lib/sqlalchemy/orm/mapper.py      Mon Jun 25 16:42:39 2012 -0400
 +++ b/lib/sqlalchemy/orm/mapper.py      Tue Jun 26 12:58:56 2012 -0400
 @@ -166,7 +166,7 @@
          # names with Mappers that will be used to construct object
 instances
          # upon a select operation.
          if _polymorphic_map is None:
 -            self.polymorphic_map = {}
 +            self.polymorphic_map = weakref.WeakValueDictionary()
          else:
              self.polymorphic_map = _polymorphic_map

 @@ -432,7 +432,8 @@
          being present."""

          # a set of all mappers which inherit from this one.
 -        self._inheriting_mappers = set()
 +        # TODO: WeakSet is only in 2.7, would need compat
 +        self._inheriting_mappers = weakref.WeakSet()

          if self.inherits:
              if isinstance(self.inherits, type):
 }}}

 {{{
 #!python
 from sqlalchemy import *
 from sqlalchemy.orm import *
 from sqlalchemy.ext.declarative import declarative_base

 Base= declarative_base()

 class Root(Base):
     __tablename__ = 'root'
     id = Column(Integer, primary_key=True)
     type = Column(String)
     __mapper_args__ = {
         'polymorphic_on':type,
         'polymorphic_identity':'root'
     }

 assert not Root.__mapper__._inheriting_mappers

 class Sub(Root):
     __tablename__ = 'sub'
     metadata = MetaData()
     id = Column(Integer, ForeignKey(Root.id), primary_key=True)
     __mapper_args__ = {
         'polymorphic_identity':'sub'
     }

 e = create_engine("sqlite://")
 Base.metadata.create_all(e)
 Sub.metadata.create_all(e)
 compile_mappers()
 s = Session(e)

 s.add_all([Root()])
 print s.query(Root).all()

 del Sub

 # this step is required, though, unless we
 # make the memoizations weak too, that would
 # be a real performance hit
 Root.__mapper__._expire_memoizations()

 import gc
 gc.collect()
 assert not Root.__mapper__._inheriting_mappers
 }}}

--

-- 
Ticket URL: <http://www.sqlalchemy.org/trac/ticket/2526#comment:1>
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