Hi everyone:
I have an object structure that uses (heavily) object orientation.
I have a "BaseObject" class that is the class for three kinds of
subclasses, "Element1", "Element2" and "Element3". In my application I
have a tree of "BaseObject" elements:
class BaseObject(declarative):
__tablename__ = "base_objects"
_polymorphicIdentity = Column("polymorphic_identity", String(20),
key="polymorphicIdentity")
__mapper_args__ = {
'polymorphic_on': _polymorphicIdentity,
'polymorphic_identity': None
}
_id = Column("id", Integer, primary_key=True, key="id")
_parentId = Column("parent_id", Integer,
ForeignKey("base_objects.id"),
key="parentId")
_children = relationship("BaseObject",
collection_class=set,
backref=backref("_parent", remote_side=lambda: BaseObject.id,
uselist=False),
#order_by=??????????????
)
class Element1(BaseObject):
__tablename__ = "elements_1"
_id = Column("id", Integer, ForeignKey(BaseObject.BaseObject.id),
primary_key=True)
__mapper_args__ = {
'polymorphic_identity': 'Element1',
'inherit_condition': _id == BaseObject.BaseObject._id,
}
_name = Column("name", String(50))
class Element2(BaseObject):
__tablename__ = "elements_2"
_id = Column("id", Integer, ForeignKey(BaseObject.BaseObject.id),
primary_key=True)
__mapper_args__ = {
'polymorphic_identity': 'Element2',
'inherit_condition': _id == BaseObject.BaseObject._id,
}
_name = Column("name", String(50))
class Element3(BaseObject):
__tablename__ = "elements_3"
_id = Column("id", Integer, ForeignKey(BaseObject.BaseObject.id),
primary_key=True)
__mapper_args__ = {
'polymorphic_identity': 'Element3',
'inherit_condition': _id == BaseObject.BaseObject._id,
}
As you can see, only two of those classes have a "_name" attribute.
What I'd like to know is if I can set an "order_by" in the
BaseObject._children relationship that does the following:
1) Sort by type, but not the default ordering. If I set up (in
_children) the order_by to order by _polymorphicIdentity (by the
discriminator), I'd get instances of type "Element1", then instances
of "Element2" and finally, from "Element3". I don't want that. I need
to get "Element1", "Element3" and finally, "Element2".
2) Sort by name if the child has a name. If it doesn't, leave it with
the 'special' _polymorphicIdentity described above if the child class
doesn't have a _name attribute.
I don't even know if that's possible.
Because of certain dependencies, I can't use SqlAlchemy 0.7.x yet. I
am using 0.6.8
Thank you very much in advance!
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