Yes, that's what I want. I already have the two relations that I
want.:
One is in Playlist, items = relationship("PlaylistItem",
cascade="all, delete", backref="playlists").
If I understand properly, this allows Playlist to contain
"PlaylistItems"
And the another one is in PlaylistItem, playlist =
relationship("Playlist", uselist=False).
This one is the one that allows the PlaylistItem to contain objects of
"Playlist" type. (Or at least, that's what I'd like it to be). This
shouldn't be pointing to its Playlist parent, but to a different
Playlist (which this item contains, because a Playlist can contain
other Playlists inside) I guess for that I'd need another
ForeignKey("playlists.id"), but I don't really know how to
differentiate this ForeignKey from the one that is pointing to its
"parent" Playlist object (or record).
Thank you for your help, btw
On Dec 7, 10:16 am, Michael Bayer <mike...@zzzcomputing.com> wrote:
> On Dec 7, 2010, at 10:09 AM, Alvaro Reinoso wrote:
>
> > 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?
>
> If you mean, you want PlaylistItem.playlist to be independent of
> Playlist.items, just use two different foreign keys and two different
> relationships. Otherwise I don't really have enough detail here to know
> what you're asking for.
>
>
>
> > 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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