On Dec 28, 2008, at 9:35 PM, Alan Shields wrote:
>
> On Sun, Dec 28, 2008 at 9:29 AM, Michael Bayer <mike...@zzzcomputing.com
> > wrote:
>> you'd put
>> "primaryjoin=crate_table.c.crate_id==crates2apples.c.some_column"
>> inside of the relation(). This approach usually makes the
>> eagerload's job easier, as far as constructing a join from
>> crate_table
>> to Apple.
>>
>> Of course the only way to know the best approach is to know exactly
>> what data you need to be loading. Its often the case that the best
>> approach overall is to use just a plain Crate->Apple relation with
>> nothing special, then just use a simple in-python property to give
>> you
>> a particular "view" of that collection. If you're dealing with
>> small
>> numbers of records that's how I'd usually do something like this. I
>> think the docs try to make a similar point on this.
>
> Several thousand records, sadly. I will probably be able to get away
> with the in-python property for
> most cases, but this is the ugly one.
>
> So, I gave that a shot and I must have messed up somewhere.
>
> crates2apples = \
> select([ crate_table.c.id.label("crate_id"),
> apple_table,
> ],
> from_obj = crate_table.\
> <bunch of joins>.outerjoin(apple_table, <condition>))
> crates2apples_a = crates2apples.alias('_crates2apples')
>
> mapper(Apple, crates2apples_a, non_primary=True)
>
> mapper(Crate, crate_table, properties={
> 'apples': relation(Apple, lazy=True, uselist=True,
> viewonly=True,
> primaryjoin= crate_table.c.id ==
> crates2apples_a.c.crate_id,
> ),
> })
you need to map to the non_primary mapper.
npapple = mapper(Apple, crates2apples_a, non_primary=True)
mapper(Crate, table, properties={
'apples':relation(npapple, ...)
})
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