Lookahead for fragments

[Matt888]

When attempting to transition from using irep_node to get the list of fields for a query, to using lookahead, this error pops up:

RuntimeError: Invariant: no field for InjectedTestFragment

On v1.8.13, query:

<<~QUERY
  query TestQuery {
    node(id: "1") {
      ...InjectedTestFragment
      id
    }
  }
QUERY

I tried returning nil like master does in lookahead.rb, but that results in no selections at all:

lookahead.selections
=> []

In irep_node, it seemed like it correctly resolved fragments, so it was straightforward to get the requested fields.

cc @swalkinshaw @dylanahsmith

[rmosolgo]

Uh oh! I think master has some improvements to lookahead, see for example #1933. (It was put on 1.9-dev, which has since been merged into master). Could you try again on master?

I'm hoping to cut a new 1.9-pre version today (waiting for #2054 at least), so if you'd rather wait for a Rubygems version, it shouldn't be long!

[Matt888]

I just used master to test, and I get the same issue where .selections is an empty array for the above query

[rmosolgo]

Oh! sorry to hear it. What is InjectedTestFragment in the query above? (I was guessing it was left out of the example since its contents could be assumed, is that right?)

I made a script to replicate it:

# __lookahead_test.rb
$LOAD_PATH << "./lib"
require "graphql"
puts GraphQL::VERSION

class Node < GraphQL::Schema::Object
  field :id, ID, null: false
end

class Query < GraphQL::Schema::Object
  field :node, Node, null: true, extras: [:lookahead] do
    argument :id, ID, required: true
  end

  def node(id:, lookahead:)
    p lookahead.selections.map(&:name)
    nil
  end
end

class Schema < GraphQL::Schema
  query(Query)
end


p Schema.execute <<-GRAPHQL
  query TestQuery {
    node(id: "1") {
      ...InjectedTestFragment
      id
    }
  }

  fragment InjectedTestFragment on Node {
    __typename
  }
GRAPHQL

But when I run it on my local master, it correctly shows both fields:

~/code/graphql-ruby $ ruby __lookahead_test.rb
1.9.0.pre2
[:__typename, :id]
#<GraphQL::Query::Result @query=... @to_h={"data"=>{"node"=>nil}}>

Can you update that example to demonstrate the failure you're observing?

[Matt888]

Sorry for the delay in getting back to you... it turns out the issue is with Interfaces. Here's the modified script:

# __lookahead_test.rb
$LOAD_PATH << "./lib"
require "graphql"
puts GraphQL::VERSION

Widget = Struct.new(:id, :name)
WIDGETS = [Widget.new("1", "foo")]

module Node
  include GraphQL::Schema::Interface

  field :id, ID, null: false

  definition_methods do
    def resolve_type(object, ctx)
      WidgetType
    end
  end
end

class WidgetType < GraphQL::Schema::Object
  implements Node

  field :name, String, null: false
end

class QueryRoot < GraphQL::Schema::Object
  field :widget, WidgetType, null: false
  field :node, Node, null: false, extras: [:lookahead] do
    argument :id, ID, required: true
  end

  def node(id:, lookahead:)
    p lookahead.selections.map(&:name)
    WIDGETS.first
  end

  def widget
    WIDGETS.first
  end
end

class Schema < GraphQL::Schema
  orphan_types WidgetType
  query(QueryRoot)
end

p Schema.execute <<~GRAPHQL
  query {
    node(id: "1") {
      id
      ... on Widget {
        name
      }
    }
  }
GRAPHQL

When this runs, we get:

1.9.0.pre2
[:id]
#<GraphQL::Query::Result @query=... @to_h={"data"=>{"node"=>{"id"=>"1", "name"=>"foo"}}}>

So the selections on the interface itself (:id) is captured, but the selections on the nested fragment are not captured.

[rmosolgo]

Ohhhh thanks for figuring that out! I'll take a look early next week and follow up here.

[rmosolgo]

Feel free to give it another go on master and let me know what you think 🍻 !

[Matt888]

Awesome!