On Mon, Apr 30, 2018 at 1:33 PM, Derek Lambert
<dlamb...@dereklambert.com> 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/
>
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--
SQLAlchemy -
The Python SQL Toolkit and Object Relational Mapper
http://www.sqlalchemy.org/
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