On Dec 17, 2011, at 11:32 AM, Kent wrote:
> Hate to bother again, but I've been down this road several times and
> even created a less than adequate solution but am determined to make
> this area more usable:
>
> Problem: I'd like to easily be able to specify to a query
> "disable_other_eagerloads", in a manner similar to
> enable_eagerloads(False), except it only affects relationships not
> specifically joined/subquery loaded for that query.
>
> I've taken to heart comments you've made more than once about avoiding
> marking lazy=False in the relationship mappings. In fact, I've seen
> they have a very evil side, I've tried to portrait them as potentially
> evil to the engineers I work with who would more happily take the lazy
> approach of eagerloading everything in the mappers so they don't have
> to think about it. I've also removed the majority of them.
>
> Still, there are relationships that, far more often than not will need
> to be joinloaded, so some are still marked as lazy=False. I suspect I
> may rip my hair out someday and remove every last one of them, but in
> the meantime, a query option that shuts off all those you haven't
> specifically mentioned in the query would be very useful.
You turn them off with the lazyload() option. Guessing you want this
generically. You'd build a function that iterates through
mapper.get_properties() for each entity in the Query, checks each
MapperProperty with isinstance(x, RelationshipProperty), checks lazy=False,
then adds it to a list. Output is a collection of lazyload() options you
send to options:
query.options(*lazyload_all_except("x", "y"))
Keep in mind this doesn't have to traverse deeply, only on the attributes that
are immediately present.
A more comprehensive way would be to subclass MapperOption and have it actually
look and see what joinedloads are already present, though that requires knowing
about the conventions that the loader options use within the query._attributes
dictionary. It also would have to be the last thing you call on options.
A feature might look like that. Or it would put in some other symbol into
query._attributes that everyone needs to check. compare to
http://www.sqlalchemy.org/trac/ticket/1418 .
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