On Sep 4, 2014, at 5:37 PM, Ken Lareau <klar...@tagged.com> wrote:
> So I have a few tables as follows (abbreviated for unnecessary columns):
>
> class Project(Base):
> __tablename__ = 'projects'
>
> id = Column(u'project_id', INTEGER(), primary_key=True)
>
> applications = relationship(
> 'AppDefinition',
> secondary=lambda: Base.metadata.tables['project_package'],
> passive_deletes=True,
> lazy=False,
> )
>
> package_definitions = relationship(
> 'PackageDefinition',
> secondary=lambda: Base.metadata.tables['project_package'],
> passive_deletes=True,
> )
>
>
> class PackageDefinition(Base):
> __tablename__ = 'package_definitions'
>
> id = Column(u'pkg_def_id', INTEGER(), primary_key=True)
>
> applications = relationship(
> 'AppDefinition',
> secondary=lambda: Base.metadata.tables['project_package'],
> passive_deletes=True,
> )
>
> projects = relationship(
> 'Project',
> secondary=lambda: Base.metadata.tables['project_package'],
> passive_deletes=True,
> )
>
>
> class AppDefinition(Base):
> __tablename__ = 'app_definitions'
>
> id = Column(u'AppID', SMALLINT(display_width=2), primary_key=True)
>
> package_definitions = relationship(
> 'PackageDefinition',
> secondary=lambda: Base.metadata.tables['project_package'],
> passive_deletes=True,
> )
>
> projects = relationship(
> 'Project',
> secondary=lambda: Base.metadata.tables['project_package'],
> passive_deletes=True,
> )
>
>
> class ProjectPackage(Base):
> __tablename__ = 'project_package'
>
> project_id = Column(
> INTEGER(),
> ForeignKey('projects.project_id', ondelete='cascade'),
> primary_key=True
> )
> pkg_def_id = Column(
> INTEGER(),
> ForeignKey('package_definitions.pkg_def_id', ondelete='cascade'),
> primary_key=True
> )
> app_id = Column(
> SMALLINT(display_width=6),
> ForeignKey('app_definitions.AppID', ondelete='cascade'),
> primary_key=True
> )
>
> app_definition = relationship('AppDefinition', uselist=False)
> package_definition = relationship('PackageDefinition', uselist=False)
> project = relationship('Project', uselist=False)
this model has serious issues, though it can be made to hobble along with some
small changes. The "three way association table" is not a great pattern in the
first place. Additionally, using that same table as "secondary" in all those
places is clearly the issue here, and they don't even have back_populates
between them, which are used in many-to-many in order to try avoid "double
deleting". But that wouldn't solve the issue here anyway.
In this case, you have mapped to the project_package table directly; you're
using the association object pattern. The note at the end of
http://docs.sqlalchemy.org/en/rel_0_9/orm/relationships.html#association-object
applies here - you absolutely should have viewonly=True on all of those
relationship() directives that refer to this association table as the
"secondary" table. The ORM otherwise has no way to know what changes should
result in what deletions where.
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