the "ImageComment" mapper is superfluous to the example. you should
generally not map a class to a table, then also use that table as the
"secondary" join in another mapping; since changes to one wont get
reflected in the other. If you want to use ImageComment, then you need
to use the association object pattern and not the "secondary" join
argument; the two patterns are mutually exclusive. for this email, ill
use the "secondary" table pattern.
SA does not keep track of all the collections that an entity belongs
to. so when you say session.delete(c), it has no idea that "c" is part
of a "comments" collection on an Image, so no operation occurs.
the solution is to remove the comment from the "comments" collection:
i = session.query(Image).get(i.id)
c = session.query(Comment).get(c.id)
i.comments.remove(c)
session.delete(c)
session.flush()
if youd like to skip the separate remove() and delete() operation, you
can use delete-orphan. for some reason, using "delete-orphan" with a
many-to-many relationship is requiring a bi-directional reference for
it to work properly...ive just added ticket # 427 for this which will
be fixed by tomorrow and the "images" backref you see below will no
longer be required.
imageMapper = mapper(Image, ImageTable,
properties={'comments': relation(Comment,
secondary=ImageCommentTable, lazy=False, cascade="all, delete-orphan",
backref="images")}
)
session = create_session()
i = Image("new")
session.save(i)
session.flush()
c = Comment("new comment")
i.comments.append(c)
session.flush()
i = session.query(Image).get(i.id)
c = session.query(Comment).get(c.id)
i.comments.remove(c)
session.flush()
session.clear()
notice above that the Comment is automatically added to the session
when its appended to the Image, this is due to the "save-update"
cascade present on the "comments" relation. If you try to save() the
Comment by itself in the session, without it being attached to any
Image, and then flush(), thats an invalid operation since its an orphan
(not attached to anything). then we remove the comment from the parent
Image object, and the delete of both the Comment and the many-to-many
record succeeds.
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