On Dec 6, 2010, at 2:39 PM, Alvaro Reinoso wrote:
> Hi all,
>
> I have those two classes:
>
> class Playlist(rdb.Model):
> """Represents playlist. It may contain playlist items"""
> rdb.metadata(metadata)
> rdb.tablename("playlists")
>
> id = Column("id", Integer, primary_key=True)
> title = Column("title", String(50))
> pending = Column("pending", Boolean)
>
> items = relationship("PlaylistItem", cascade="all, delete",
> backref="playlists")
> screens = relationship("Screen", secondary=playlist_screens,
> backref="playlists")
>
> class PlaylistItem(rdb.Model):
> """Represents a playlist of items in Schedule page"""
> rdb.metadata(metadata)
> rdb.tablename("playlist_items")
>
> id = Column("id", Integer, primary_key=True)
> title = Column("title", String(50))
> runtime = Column("runtime", Integer)
> layoutId = Column("layout_id", Integer, ForeignKey("layouts.id"))
> playlistId = Column("playlist_id", Integer,
> ForeignKey("playlists.id"))
>
> layout = relationship("Layout", uselist=False)
> playlist = relationship("Playlist", uselist=False)
>
> One playlist can contain many PlaylistItem and PlaylistItem could
> contain layout or another playlist. The problem is when adding a
> PlaylistItem to a Playlist, PlaylistItem automatically gets the id of
> its parent (playlist_id). How can I avoid this?
>
> Thanks in advance!
the "items" collection of Playlist represents a one-to-many reference to a list
of PlaylistItems. A PlaylistItem in turn can only be referenced by one
parent. The items/playlists relationships therefore manage the "playlistId"
attribute to be the one foreign key represented by this ownership. If a
PlaylistItem is capable of having multiple Playlist parents, this relationship
should be changed to a many-to-many. Reference on relationship() patterns is
at
http://www.sqlalchemy.org/docs/orm/relationships.html#basic-relational-patterns
.
>
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