>
>
> mmm what do you mean by "mixin" here, it looks like every class you
> have is mapped.
>
>
They are mapped in the code, but that's only so I can query them. I
attempted to make LdapEntry and ActiveDirectoryEntry true mixin's by
setting __abstract__ = True.
>
> this a heavy set of inheritance and I might also use composition
> instead, though that would change your DB design.
>
>
The design isn't in production yet so now would be the time to change it.
Are you aware of any SQLAlchemy projects using composition I could review?
Thanks,
Derek
On Monday, April 30, 2018 at 1:30:51 PM UTC-5, Mike Bayer wrote:
> On Mon, Apr 30, 2018 at 1:33 PM, Derek Lambert
> <dlam...@dereklambert.com <javascript:>> wrote:
> > I'm running into an issue in a hierarchy of single-table inheritance
> objects
> > with multiple inheritance. The objects represent users/groups/etc. from
> > various directories and applications.
> >
> > Retrieving the list of synonyms from an object at the bottom of the
> > inheritance tree doesn't return the entire list of synonyms.
> >
> > When I make some of the "mixin" type objects abstract the synonyms
> returned
> > are as expected, but I lose the ability to query those objects.
>
> mmm what do you mean by "mixin" here, it looks like every class you
> have is mapped.
>
> I will say that what you are doing here:
>
> class LdapUser(DirectoryUser, LdapEntry):
> givenName = orm.synonym('first_name')
> sn = orm.synonym('last_name')
> __mapper_args__ = {
> 'polymorphic_identity': 'ldap_user',
> }
>
> where DirectoryUser and LdapEntry are also both mapped, I'm amazed
> that even works. That's not at all anything that has ever been
> supported or attempted, as each mapper only "inherits" from at most
> one mapped class - while declarative supports actual "mixin" classes,
> where by "mixin" we mean "non-mapped class", nothing in SQLAlchemy ORM
> is expecting multiple inheritance at the mapper level. Above, I
> guess it's picking one superclass mapper at random to be "inherits",
> an ignoring the other, and that is likely the source of your issue.
> Unfortunately I think you have to work out this hierarchy in terms of
> single-inhertanace for classes that are actually mapped, which means
> adding some non-mapped "mixin" classes that just accommodate for the
> extra synonyms, something like:
>
> class DirectoryEntry(Base):
>
> class AbstractDirectoryUser(object):
> # synonyms
>
> class DirectoryUser(AbstractDirectoryUser, DirectoryEntry):
>
> class LdapEntry(DirectoryEntry):
>
> class LdapUser(AbstractDirectoryUser, LdapEntry):
>
> this a heavy set of inheritance and I might also use composition
> instead, though that would change your DB design.
>
>
> >
> > Maybe I'm overlooking a simpler implementation, or simply using
> SQLAlchemy
> > in a way that wasn't intended?
> >
> > Here's a simplified subset of the code. In practice any object ending
> with
> > Entry and the base DirectoryUser and DirectoryGroup wouldn't be created.
> >
> > import sqlalchemy as sa
> > import sqlalchemy.orm as orm
> > from sqlalchemy.ext.declarative import declarative_base
> >
> >
> > Base = declarative_base()
> >
> >
> > class DirectoryEntry(Base):
> > guid = sa.Column(sa.Integer, primary_key=True)
> > _type = sa.Column(sa.String, nullable=False,
> index=True)
> > distinguished_name = sa.Column(sa.String, index=True)
> > name = sa.Column(sa.String, index=True)
> >
> > __tablename__ = 'directory_entry'
> > __mapper_args__ = {
> > 'polymorphic_on': _type,
> > 'polymorphic_identity': 'directory_entry',
> > }
> >
> >
> > class DirectoryUser(DirectoryEntry):
> > first_name = sa.Column(sa.String)
> > last_name = sa.Column(sa.String)
> > email = sa.Column(sa.String)
> > username = sa.Column(sa.String)
> >
> > __mapper_args__ = {
> > 'polymorphic_identity': 'directory_user',
> > }
> >
> >
> > class LdapEntry(DirectoryEntry):
> > cn = orm.synonym('name')
> >
> > __mapper_args__ = {
> > 'polymorphic_identity': 'ldap_entry',
> > }
> >
> >
> > class LdapUser(DirectoryUser, LdapEntry):
> > givenName = orm.synonym('first_name')
> > sn = orm.synonym('last_name')
> >
> > __mapper_args__ = {
> > 'polymorphic_identity': 'ldap_user',
> > }
> >
> >
> > class ActiveDirectoryEntry(LdapEntry):
> > distinguishedName = orm.synonym('distinguished_name')
> >
> > __mapper_args__ = {
> > 'polymorphic_identity': 'active_directory_entry',
> > }
> >
> >
> > class ActiveDirectoryUser(LdapUser, ActiveDirectoryEntry):
> > mail = orm.synonym('email')
> > sAMAccountName = orm.synonym('username')
> >
> > __mapper_args__ = {
> > 'polymorphic_identity': 'active_directory_user'
> > }
> >
> >
> > engine_url = 'postgresql+psycopg2://postgres@localhost/inherit_test'
> > engine = sa.create_engine(engine_url, echo=True)
> >
> > Base.metadata.create_all(engine)
> >
> > session = orm.sessionmaker(bind=engine)()
> > ad_user = ActiveDirectoryUser(
> > cn='John Doe',
> > sAMAccountName='jdoe',
> > distinguishedName='ou=domain',
> > givenName='John'
> > )
> >
> > session.add(ad_user)
> > session.commit()
> >
> > user1 = session.query(DirectoryUser).filter(DirectoryUser.username ==
> > 'jdoe').one()
> > user3 = session.query(LdapUser).filter(LdapUser.username ==
> 'jdoe').one()
> > user2 =
> > session.query(ActiveDirectoryUser).filter(ActiveDirectoryUser.username
> ==
> > 'jdoe').one()
> > user4 = session.query(DirectoryEntry).filter(DirectoryEntry.name ==
> 'John
> > Doe').one()
> >
> > assert(user1 == user2 == user3 == user4)
> >
> > mapper = sa.inspect(ad_user.__class__)
> > synonyms = mapper.synonyms.keys()
> >
> > assert(synonyms == ['mail', 'sAMAccountName', 'givenName', 'sn', 'cn',
> > 'distinguishedName'])
> >
> >
> > Any help is appreciated!
> >
> > --
> > SQLAlchemy -
> > The Python SQL Toolkit and Object Relational Mapper
> >
> > http://www.sqlalchemy.org/
> >
> > To post example code, please provide an MCVE: Minimal, Complete, and
> > Verifiable Example. See http://stackoverflow.com/help/mcve for a full
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--
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The Python SQL Toolkit and Object Relational Mapper
http://www.sqlalchemy.org/
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