Promises fail to be resolved for Relay connection_type

[joshjcarrier]

Relay support in graphql-ruby suggests resolvers for a connection_type should be able to return an array. Expect that graphql-batch would support field resolver returning promise of an array in this scenario. It instead fails with exception No connection implementation to wrap GraphQL::Batch::Promise.

A workaround is to have the resolver wait for promise fulfillment by calling Promise#sync on the Loader#load/#load_many result.

@cjoudrey @dylanahsmith

For a repro, consider this script using graphql (0.19.4) and graphql-batch (0.2.4) on ruby 2.3.0p0 (2015-12-25 revision 53290) [x86_64-darwin15]:

require 'graphql/batch'

class ShopLoader < GraphQL::Batch::Loader
  def initialize(ctx)
  end

  def perform(ids)
    ids.each { |id| fulfill(id, OpenStruct.new({ id: id })) }
  end
end

class ShopResolver
  def self.call(obj, args, ctx)
    ShopLoader.for("ctx").load_many([ 1, 2, 3 ])
  end
end

ShopType = GraphQL::ObjectType.define do
  name "Shop"

  field :id do
    type types.ID
  end
end

QueryType = GraphQL::ObjectType.define do
  name "Query"

  field :shops do
    type types[ShopType]
    resolve ShopResolver
  end

  connection :shopsConnection, ShopType.connection_type do
    resolve ShopResolver
  end
end

Schema = GraphQL::Schema.define do
  query QueryType
end

Schema.query_execution_strategy = GraphQL::Batch::ExecutionStrategy
Schema.mutation_execution_strategy = GraphQL::Batch::MutationExecutionStrategy

puts "Array use of cache loader:"
puts Schema.execute("{ shops { id } }")
# {"data"=>{"shops"=>[{"id"=>"1"}, {"id"=>"2"}, {"id"=>"3"}]}}

puts "Connection use of cache loader:"
puts Schema.execute("{ shopsConnection { edges { node { id } } } }")
# /Users/jocarrie/.rvm/gems/ruby-2.3.0/gems/graphql-0.19.4/lib/graphql/relay/base_connection.rb:37:in `connection_for_nodes': 
# No connection implementation to wrap GraphQL::Batch::Promise (#<GraphQL::Batch::Promise:0x007f8081152170>) (RuntimeError)
#   from /Users/jocarrie/.rvm/gems/ruby-2.3.0/gems/graphql-0.19.4/lib/graphql/relay/connection_resolve.rb:12:in `call'

[dylanahsmith]

Now that graphql-relay-ruby has been merged into graphql-ruby, we could probably be clearer about the fact that the relay code in graphql-ruby isn't supported by graphql-batch.

We mention in the README that

The loader class can be used from the resolve proc for a graphql field

and in this case you are trying to use the loader in a connection resolve proc, not on the field resolve proc.

You may be able to support this by using GraphQL::Relay::BaseConnection.register_connection_implementation.

[joshjcarrier]

Here's the simplest thing I could do convert over:

module GraphQL
  module Batch
    class SyncPromiseConnection < GraphQL::Relay::ArrayConnection
      def nodes
        super.sync
      end
    end
  end
end

GraphQL::Relay::BaseConnection.register_connection_implementation(GraphQL::Batch::Promise, GraphQL::Batch::SyncPromiseConnection)

At least it lets this gem work by default with connections? Is it worth further investment (concern that it extends GraphQL::Relay::ArrayConnection which is subject to breakage)?

[dylanahsmith]

Calling sync like that would prevent batching.

With graphql-ruby's new lazy execution API it will actually be possible to fix this upstream, so I'm going to consider this an upstream issue now and close the issue here.

[rmosolgo]

Upstream fix here!

rmosolgo/graphql-ruby#425

[mengqing]

Is there an example on how to implement this? Using the association loader in the example folder would produce N+1 on connection types