Incidentally, I tried mocking this all up entirely outside of SA by
creating a DictOfLists class that subclasses the basic 'dict'. That
worked fine, returns lists, adds and removes as desired, handles
everything as one would expect. So I don't think I'm fumbling with
the basic mechanics of it.
On Feb 15, 11:41 pm, Eric Ongerth <[EMAIL PROTECTED]> wrote:
> Ok, I tried subclassing MappedCollection and it seems like I did all
> right with my made-up appender, remover, and iterator functions. At
> least I fixed various errors and got this to at least function as the
> collection_class for the mapper shown above.
>
> But I can't figure out how to tell my DictOfLists to return a list
> instead of a single item. So there's a place where I'm trying to say:
> for child in some_bar.children[some_foo]:
> blah(child)
> etc.
>
> Sadly, while some_bar.children[some_foo] at least returns something,
> it returns a scalar Bar instance, not a list of Bars as I want it too.
>
> What's the next step?
>
> On Feb 15, 8:21 pm, Eric Ongerth <[EMAIL PROTECTED]> wrote:
>
> > In case I didn't make it clear enough -- I've already done the
> > following:
>
> > 'children': relation(Bar,
> > collection_class=attribute_mapped_collection('foo'),
> > backref=backref('parent', remote_side=[bars.c.id])) } )
>
> > And that worked great -- if I only needed to have up to a SINGLE child
> > per bar per foo. Because the dict in attribute_mapped_collection
> > expects scalar keys and scalar values, right? It's not set up to
> > collect a whole list of values per key. And that is what I need. Any
> > given Foo is only going to appear once in the keys of any given Bar's
> > children DictOfLists, of course. But the values mapped to that given
> > Foo need to be a list of Bars of any length. Any given Bar will have
> > 1..n children in the bars table; each of these child Bars will be
> > related to a single Foo, but the total number of Foos is < n, so a
> > parent Bar might have a number of child Bars for a given Foo, while
> > only having zero or one single child Bar for some other Foo.
>
> > There, I think that tells it more completely. Sorry for the
> > metasyntactic variables.
>
> > On Feb 15, 8:13 pm, Eric Ongerth <[EMAIL PROTECTED]> wrote:
>
> > > If anyone out there has already implemented a custom DictOfLists
> > > collection class to map scalar keys to lists of values, I would be
> > > grateful for the opportunity to avoid reinventing the wheel. If not,
> > > I guess I'll start working on it.
>
> > > I've experimented successfully with attribute_mapped_collection and
> > > column_mapped_collection and they work just great. However, instead
> > > of mapping keys to single values, I need some of my mapper relations
> > > to map to a list of values.
>
> > > Here is more of the picture, for example.
>
> > > foos = Table('foos', metadata,
> > > Column('id', Integer, primary_key=True),
> > > Column('name', String(20)))
>
> > > bars = Table('bars', metadata,
> > > Column('id', Integer, primary_key=True),
> > > Column('foo_id', Integer, ForeignKey('foos.id')),
> > > Column('value', String(20)),
> > > Column('parent_id', Integer, ForeignKey('bars.id')))
>
> > > class Foo(object): pass
> > > class Bar(object): pass
>
> > > mapper(Foo, foos)
>
> > > mapper(Bar, bars, properties={
> > > 'foo':relation(Foo, uselist=False, backref='bars'),
> > > 'children':relation(Bar,
> > > backref=backref('parent',
> > > remote_side=[bars.c.id]))
>
> > > })
>
> > > ... So we have a relation of 1 Foo : many Bars. And within the Bars
> > > we also have 'adjacency' (tree-like) relations between the various
> > > rows of the 'bars' table. A Bar's children are kept in the standard
> > > list-like collection class.
>
> > > But what I really need is a *dict* instead of a list. Ok, SA already
> > > takes care of that. But I actually need a list-like collection to
> > > appear as the value for each key in the dict. Specifically, I need
> > > each Bar to be able to have stored children *per Foo*. And not keyed
> > > by the parent's foo, but the child's foo.
>
> > > Does that make sense? I'll be working on this immediately, but if
> > > anyone can shorten my path to getting this straight I'd be very glad.
> > > I'm beginning to work out the use of a custom collection_class for
> > > this, but I haven't done all that much with metaclassing and the way
> > > forward isn't obvious (the SA instructions about this seem to assume
> > > the programmer is pretty experienced with custom subclassing etc.)
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