[LRUG] Advice: manipulating ActiveRecord objects [newbie]

[Duncan Stuart]

Is it just a case of putting the `where` before the `includes`?

i.e. is it potentially loading all of the included models first and THEN
filtering them by account ID?

On 14 December 2015 at 12:46, Marco Iannone <marco.iannone at gmail.com> wrote:

> ​Hello,
>
> ​
> Ruby newbie question alert
> ​: many apologies if it's too basic, or not the type of questions for this
> forum.
> At least I can say we tried hard before going to StackOverflow
> <http://stackoverflow.com/questions/34227034/manipulating-activerecord-objects-to-build-json>
> ​, and now here.​
>
>
> We're trying to
> ​ensure a webpage loads faster. The main issue
> ​relates to a few activerecord-generated queries on that page.
>
> If you look at the SQL they generate, the queries are as follows (all code
> a bit simplified):
>
> select * from feed_details where account_id = 5
> select * from feeds where id in (VERY_LONG_LIST_OF_IDS_FROM_FIRST_QUERY)
> select * from feeds_metadata where feed_id in
> (VERY_LONG_LIST_FROM_FIRST_QUERY)
> select * from documents where feed_id in (VERY_LONG_LIST_FROM_FIRST_QUERY)
>
> All the indexes are in place, but we verified that they'd take less than
> half the time by changing
> ​each of them to:
>
> select * from feeds, feed_details where id = feed_id and account_id = 5
> select * from feeds_metadata fm, feed_details fd where fm.feed_id =
> fd.feed_id and account_id = 5
> select * from documents where d, feed_details fd where d.feed_id =
> fd.feed_id and account_id = 5
>
> So far, so simple.
>
> Here is the
> ​Rails issue: these queries have been generated by this code in the
> FeedDetail model:
>
> class FeedDetail < ActiveRecord::Base
>
>   has_many :feeds
>   has_many :feeds_metadata
>   has_many :documents
>
>   scope :feeds_data_for_account, ->(current_account_id) do
>     FeedDetail
>               .includes(:feeds, :feeds_metadata, :documents)
>               .where(
>                   account_id: current_account_id
>               )
>   end
>
> This generates an active record object with the data from the
> above-mentioned queries, that is used in the controller to build the JSON
> that is sent to the webpage as in below (see feeds_data line):
>
>   def index
>     consumer          = ConsumerWithAccount.new(current_user.account)
>     feed_builder      = FeedBuilder
>     feeds_data        = FeedDetail.feeds_data_for_account(
> current_user.account.id)
>
>     render json: ResponseBuilder.new(consumer, feed_builder, feeds_data)
>   end
>
> To use the faster queries, we were hoping to build the feeds_data
> activerecord object
> ​​by using the faster queries; this gets passed to the JSON builder​. That
> would
> ​seem to require getting rid of the "involves", which (seemingly) uses the
> IN ().
>
> If useful, we have the
> ​more effective activerecord for the 3 queries, they look like:
> Feed.joins(:feed_details).where(feed_document_sets: {account_id:
> current_account_id})
>
> But we couldn't figure out how to build that
> ​ ​
> ​activerecord object
> ​, or one that can be parsed in a similar way by the responsebuilder​
> : therein lies the proverbial rub.
>
> Intense googling and referring to rails docs hasn't helped.​
>
>
> The plan B
> ​would be to re-write the responsebuilder to take a different type of
> object, but that looks more complicated.
>
> The person who wrote this is no longer with the company.
>
> Plan C is to shake very hard the computer and hope for the best.
>
> Any suggestions would be much appreciated
> ​, off/on list​
> .
>
> ​Thanks,
> Marco​
>
>
> _______________________________________________
> Chat mailing list
> Chat at lists.lrug.org
> Archives: http://lists.lrug.org/pipermail/chat-lrug.org
> Manage your subscription: http://lists.lrug.org/options.cgi/chat-lrug.org
> List info: http://lists.lrug.org/listinfo.cgi/chat-lrug.org
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.lrug.org/pipermail/chat-lrug.org/attachments/20151214/7cf52dd5/attachment-0002.html>