funny, that's absolutely a bug and it works in declarative because the same fix
you have there was already applied some time ago within declarative. this is
#2153 targeted at 0.6.8 so I will get to it when i make a pass through a set of
small 0.6.8 issues later in the week.
On Apr 28, 2011, at 10:40 AM, Torsten Landschoff wrote:
> Hello world!
>
> I am currently trying to transform my code from classic (schema defined in an
> extra python module) to declarative. As intermediate step I am moving the
> table definitions to the class implementations.
>
> What I am running into is sketched in the following example. In reality, I
> have different modules for Base, Derived and Owner.
>
> -------
> from sqlalchemy import *
> from sqlalchemy.orm import *
>
> metadata = MetaData()
>
> class Base(object): pass
>
> base_table = Table("base", metadata,
> Column("id", Integer, primary_key=True),
> Column("target_type", String))
>
> mapper(Base, base_table, polymorphic_on=base_table.c.target_type)
>
>
> class Derived(Base): pass
>
> derived_table = Table("derived", metadata,
> Column("id", Integer, ForeignKey("base.id"), primary_key=True),
> Column("owner_id", Integer, ForeignKey("owner.owner_id"), nullable=False))
>
> mapper(Derived, derived_table, polymorphic_identity="derived", inherits=Base)
>
>
> class Owner(object): pass
>
> owner_table = Table("owner", metadata,
> Column("owner_id", Integer, primary_key=True))
>
> mapper(Owner, owner_table)
> -------
>
> Running this gives me the following exception:
>
> Traceback (most recent call last):
> File "inherit_problem.py", line 21, in <module>
> mapper(Derived, derived_table, polymorphic_identity="derived",
> inherits=Base)
> File
> "/usr/local/lib/python2.6/dist-packages/SQLAlchemy-0.6.8dev-py2.6.egg/sqlalchemy/orm/__init__.py",
> line 890, in mapper
> return Mapper(class_, local_table, *args, **params)
> File
> "/usr/local/lib/python2.6/dist-packages/SQLAlchemy-0.6.8dev-py2.6.egg/sqlalchemy/orm/mapper.py",
> line 208, in __init__
> self._configure_inheritance()
> File
> "/usr/local/lib/python2.6/dist-packages/SQLAlchemy-0.6.8dev-py2.6.egg/sqlalchemy/orm/mapper.py",
> line 259, in _configure_inheritance
> self.local_table)
> File
> "/usr/local/lib/python2.6/dist-packages/SQLAlchemy-0.6.8dev-py2.6.egg/sqlalchemy/sql/util.py",
> line 227, in join_condition
> col = fk.get_referent(left)
> File
> "/usr/local/lib/python2.6/dist-packages/SQLAlchemy-0.6.8dev-py2.6.egg/sqlalchemy/schema.py",
> line 1161, in get_referent
> return table.corresponding_column(self.column)
> File
> "/usr/local/lib/python2.6/dist-packages/SQLAlchemy-0.6.8dev-py2.6.egg/sqlalchemy/util.py",
> line 1517, in __get__
> obj.__dict__[self.__name__] = result = self.fget(obj)
> File
> "/usr/local/lib/python2.6/dist-packages/SQLAlchemy-0.6.8dev-py2.6.egg/sqlalchemy/schema.py",
> line 1223, in column
> "foreign key to target column '%s'" % (self.parent, tname, colname))
> sqlalchemy.exc.NoReferencedTableError: Foreign key assocated with column
> 'derived.owner_id' could not find table 'owner' with which to generate a
> foreign key to target column 'owner_id'
>
> The solution is of course to define all the tables first and do the mapping
> only after that. This would put me back to point one.
>
>
> I tried to get around this by patching SA with this patch:
>
> -------
> diff -r 27fec7a0e05f lib/sqlalchemy/orm/mapper.py
> --- a/lib/sqlalchemy/orm/mapper.py Wed Apr 27 12:51:50 2011 -0400
> +++ b/lib/sqlalchemy/orm/mapper.py Thu Apr 28 16:26:57 2011 +0200
> @@ -256,7 +256,8 @@
> # want (allows test/inheritance.InheritTest4 to pass)
> self.inherit_condition = sqlutil.join_condition(
>
> self.inherits.local_table,
> - self.local_table)
> + self.local_table,
> +
> ignore_nonexistent_tables=True)
> self.mapped_table = sql.join(
> self.inherits.mapped_table,
> self.local_table,
> -------
>
> This makes the example work, but I'd rather stay with an official SQLAlchemy.
> So would it be possible to make this work out of the box? Is there a better
> way to implement this?
>
> Any hints are greatly appreciated.
>
> Torsten
>
> PS: I just tried to implement this in a declarative way. This seems to work
> fine:
>
> -------
> from sqlalchemy import *
> from sqlalchemy.orm import *
> from sqlalchemy.ext.declarative import declarative_base
>
> DeclBase = declarative_base()
>
> class Base(DeclBase):
> __tablename__ = "base"
> id = Column(Integer, primary_key=True)
> target_type = Column(String)
>
> __mapper_args__ = { "polymorphic_on": target_type }
>
>
> class Derived(Base):
> __tablename__ = "derived"
> id = Column(Integer, ForeignKey(Base.id), primary_key=True)
> owner_id = Column(Integer, ForeignKey("owner.owner_id"), nullable=False)
> owner = relationship("Owner")
>
> __mapper_args__ = { "polymorphic_identity": "derived" }
>
>
> class Owner(DeclBase):
> __tablename__ = "owner"
> owner_id = Column(Integer, primary_key=True)
>
> engine = create_engine("sqlite:///:memory:", echo=True)
> DeclBase.metadata.create_all(engine)
> session = sessionmaker(engine)()
>
> owner = Owner()
> derived = Derived(owner=owner)
> session.add(derived)
> session.commit()
> -------
>
> However, I already failed to do the whole conversion in one giant commit,
> therefore I would prefer to do it in small steps.
>
> --
> DYNAmore Gesellschaft fuer Ingenieurdienstleistungen mbH
> Torsten Landschoff
>
> Office Dresden
> Tel: +49-(0)351-4519587
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>
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>
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