The relation is OK, one-to-many between Playlist and PlaylisItem.
However, PlaylistItem can contain one Playlist or one Layout and that
Playlist could be in many PlaylistItems. I know it's weird relation if
I already have Playlist as parent of PlaylistItem, but could I get
this?
Thanks!
On Dec 6, 3:51 pm, Michael Bayer <mike...@zzzcomputing.com> wrote:
> 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
> athttp://www.sqlalchemy.org/docs/orm/relationships.html#basic-relationa....
>
>
>
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