On Tuesday, July 21, 2015 at 3:59:37 AM UTC-6, Lin Jen-Shin wrote:
>
> I am trying to use use_cursor with eager,
> but use_cursor requires to use each,
> which didn't work well with eager. Any advise?
>
> Thanks!
>
> For now, I am doing something like this to
> simulate it:
>
> query.use_cursor(:rows_per_fetch => 100).each_slice(100) do |records|
> assocs = Assoication.where(:id => records.map(&:association_id)).all
> records.each do |r|
> r.association = assocs.find{ |a| a.id == r.association_id }
> end
> end
>
> It would be great if there's a better way to do this.
>
> p.s. use_cursor:
>
> http://sequel.jeremyevans.net/rdoc-adapters/classes/Sequel/Postgres/Dataset.html#method-i-use_cursor
>
>
This isn't specific to or even really related to #use_cursor, it's that
eager loading doesn't work with Dataset#each, it's handled inside
Dataset#all. In order to eagerly load associated records, you need to have
all the current records. What you are doing is a separate eager-ish load
for every 100 records, which isn't really the same thing as a eager load
for the whole set. For one thing, let's say in each of the 100-record
sets, the same associated record is needed. You end up with a separate
associated record each eager-ish load, instead of having all of the records
have a reference to the same object (which is what a true eager load does).
I'm glad you were able to get something that works for your use case, but
this isn't something I plan to support in Sequel. A slightly easier way
may be:
# completely untested
query.eager(:association).each_slice(100) do |records|
query.send(:eager_load, records)
end
Thanks,
Jeremy
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