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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