Loading associations of multiple records creates N+1 queries

[ChrisKaun]

Hey,
found this fork while trying to upgrade my application to rails v6, which didn't work because the original repo isn't maintained anymore, so first of all: Thanks for sharing your work.

I've run into a problem when loading multiple records. The app is on rails 5.2.6 and graphql 1.12.8.

A offer has a assigned customer.

module Types
  class OfferType < Types::BaseObject
    graphql_name 'Offer'
    field :customer, Unions::ContactsUnion, null: false do
      preload :customer
    end
  end
end

When loading multiple offers and their customers the customers are not loaded in a single sql-query

query offers {
  offers(ids: [6, 7]) {
    id
    customer {
      ... on Company {
        id
      }
    }
  }
}

Offer Load (0.5ms)  SELECT "offers".* FROM "offers" WHERE "offers"."id" IN ($1, $2)  [["id", 6], ["id", 7]]
Company Load (0.6ms)  SELECT  "companies".* FROM "companies" WHERE "companies"."id" = $1 LIMIT $2  [["id", 4], ["LIMIT", 1]]
Company Load (0.4ms)  SELECT  "companies".* FROM "companies" WHERE "companies"."id" = $1 LIMIT $2  [["id", 1], ["LIMIT", 1]]

I've tested this repo with my current production branch, where i simply replaced the ConsultingMD repo version with this forks version and everything worked as expected, so I guess this might have something to do with the newer graphql version I've installed.
The following deprecation warning gets raised once I trigger a query:

DEPRECATION WARNING: Field instrumentation (#<GraphQL::Preload::Instrument:0x00007f61b733bf38>) will be removed in GraphQL-Ruby 2.0, please upgrade to field extensions: https://graphql-ruby.org/type_definitions/field_extensions.html (called from enable_preloading at /home/xx/xxx/vendor/bundle/bundler/gems/graphql-preload-5040f7851bca/lib/graphql/preload.rb:28)

Is it possible that the issue I'm facing comes from the new GraphQL version?

[Envek]

That's possible. If you have some time you can clone this repo and try to add new graphql-ruby version into Appraisals file and run specs against it to check if this is the case.

I don't have capacity now to do anything for this fork.

[ChrisKaun]

Thanks for the quick answer, cloned the repo and tested it against the current GraphQL Version.

Failures:

  1) GraphQL::Preload modern class-based GraphQL schema with associations with custom scopes preloads associations by single query and given order
     Failure/Error: expect { subject }.not_to exceed_query_limit 2

       Expected to run maximum 2 queries
       The following 3 queries were invoked:
          1) SELECT "users".* FROM "users" (0.036 ms)
          2) SELECT "posts".* FROM "posts" WHERE "posts"."author_id" = ?; [1]  (0.071 ms)
          3) SELECT "posts".* FROM "posts" WHERE "posts"."author_id" = ?; [2]  (0.034 ms)

If I find the time I will try to fork the repo and fix this.

[Envek]

I believe that it is duplicate of #3 due to the fact that interpreter runtime is enabled by default since GraphQL-Ruby 1.12.0:

It is the default runtime since 1.12.0.

See GraphQL-Ruby docs for Interpreter runtime.