Recursive schema definition potentially causing an infinite loop

[Bockit]

Hi. Firstly, thanks for all the work on graphql-elixir and plug-graphql.

I'm having trouble with a circular schema definition. Using plug_graphql in phoenix and the server freezes up no matter the query when the circular definitions are in play.

• Recurring
• Transaction
• Tag

Relations are:

• Tags many to many Recurring
• Tags many to many Transaction

https://github.com/Bockit/budget/tree/master/apps/api-server/web/graphql is the graphql schema I have for this model. The root query provides a singular and list type query for each model. Each model has a resolve tag for its relations.

Before I added the relations to the Tag schema, things were great but once I added the recurrings and transactions relations to the Tag schema all requests freeze up in what appears to be an infinite loop. Even if you don't request any of the relation fields.

If you comment out the tags field on Transaction, and the recurrings field on Tag (breaking the circle) then you can do the following and it works as expected:

$ curl "http://127.0.0.1:4000/api?query=\{recurring(id:11)\{amount,tags\{tag,transactions\{amount\}\}\}\}"
{
  "data": {
    "recurring": {
      "tags": [
        {
          "transactions": [
            {
              "amount": 24.53
            }
          ],
          "tag": "Utilities"
        },
        {
          "transactions": [
            {
              "amount": 60.0
            }
          ],
          "tag": "Development"
        }
      ],
      "amount": 50.0
    }
  }
}

If this is confusing I can make a simpler, proof-of-concept reproduction tomorrow. If I'm correct and this is causing an infinite loop with a circular reference as described then a simple schema with 2 object types that both refer back to each other should cause the same effect.

Thanks for your time.

[joshprice]

Thanks for the bug report! I'll see if can reproduce this and let you know if I have any questions.

[Bockit]

@joshprice I put together a reproduction as a test and it passes so it looks like things are good. I think the infinite loop is me calling schema, calling schema, calling schema, calling schema in my definitions.

If you want the test in here I can make it a PR, otherwise I'll drop the branch. Either way, I think this issue is closable. Sorry if you wasted any time on it!

[joshprice]

Hadn't had a chance to look at it yet, but glad you got to the bottom of it. A PR with that recursion test in would be fantastic thanks!

[Bockit]

Turns out my test wasn't a circular dep, if I went any levels deeper it wouldn't work because elixir isn't mutable and my last reference to fruit in basket doesn't have a basket field.

Basically something like this that I would do in node isn't something I can do in elixir.

var a = {}
var b = {}
b.a = a
a.b = b

console.log(a.b.a.b.a.b.a.b === b) // true

Which in a long story short is to say in the end it's not testing anything you aren't already testing :)

Just had a chat about it in #general in the elixir slack. The tip about recursive traversal algorithms is intriguing but seeing as the use case I have for it can be solved by using my own recursion for how deep I define the schema I'm going to go with that and the recursive algorithm traversal is probably way out of scope for this library.

[markolson]

So, I saw this Issue just before starting to travel, and ended up coming with a solution ( #39 ) analogous to the js reference implementation of graphql. Where they wrap the fields in an anonymous function to delay execution, I think we can quote ours.

[Bockit]

Thanks @markolson, really great!

[ashleyw]

I'm using @markolson's fix (#39), however with graphql-relay, running GraphQL.Relay.generate_schema_json! throws this error:

[debug] Updating GraphQL schema.json
** (FunctionClauseError) no function clause matching in GraphQL.Type.CompositeType.do_get_fields/1
    (graphql) lib/graphql/type/composite_type.ex:33: GraphQL.Type.CompositeType.do_get_fields({:%{}, [], [max_score: {:%{}, [], [type: {:%, [], [{:__aliases__, [alias: false], [:GraphQL, :Type, :Float]}, {:%{}, [], []}]}, resolve: {:fn, [], [{:->, [], [[{:_, [], VideoSchema}, {:_, [], VideoSchema}, {:_, [], VideoSchema}], 1]}]}]}, videos: {:%{}, [], [type: {{:., [], [Access, :get]}, [], [{:video_connection, [], VideoSchema}, :connection_type]}, args: {{:., [], [{:__aliases__, [alias: GraphQL.Relay.Connection], [:Connection]}, :args]}, [], []}, resolve: {:fn, [], [{:->, [], [[{:videos, [], VideoSchema}, {:args, [], VideoSchema}, {:_ctx, [], VideoSchema}], {:__block__, [], [{{:., [], [{:__aliases__, [alias: false], [:IO]}, :inspect]}, [], [{:args, [], VideoSchema}]}, {:=, [], [{:cursor_count, [], VideoSchema}, {:try, [], [[do: {{:., [], [{:__aliases__, [alias: GraphQL.Relay.Connection.List], [:Connection, :List]}, :cursor_to_offset]}, [], [{:||, [context: VideoSchema, import: Kernel], [{{:., [], [Access, :get]}, [], [{:args, [], VideoSchema}, :after]}, {{:., [], [Access, :get]}, [], [{:args, [], VideoSchema}, :before]}]}]}, rescue: [{:->, [], [[{:__aliases__, [alias: false], [:FunctionClauseError]}], 0]}]]]}]}, {:=, [], [{:count, [], VideoSchema}, {:+, [context: VideoSchema, import: Kernel], [{:+, [context: VideoSchema, import: Kernel], [{:cursor_count, [], VideoSchema}, {{:., [], [Access, :get]}, [], [{:args, [], VideoSchema}, :first]}]}, 1]}]}, {{:., [], [{:__aliases__, [alias: GraphQL.Relay.Connection.List], [:Connection, :List]}, :resolve]}, [], [{:videos, [], VideoSchema}, {:args, [], VideoSchema}]}]}]}]}]}]})
    (graphql) lib/graphql/type/schema.ex:56: GraphQL.Schema.reduce_types/2
    (stdlib) lists.erl:1262: :lists.foldl/3
    (graphql) lib/graphql/type/schema.ex:57: GraphQL.Schema.reduce_types/2
    (stdlib) lists.erl:1262: :lists.foldl/3
    (graphql) lib/graphql/type/schema.ex:57: GraphQL.Schema.reduce_types/2
    (graphql) lib/graphql/type/schema.ex:31: GraphQL.Schema.reduce_types/1
    (graphql) lib/graphql/type/schema.ex:26: GraphQL.Schema.type_from_ast/2
    (graphql) lib/graphql/lang/ast/type_info_visitor.ex:100: GraphQL.Lang.AST.Visitor.GraphQL.Lang.AST.TypeInfoVisitor.enter/3
    (graphql) lib/graphql/lang/ast/composite_visitor.ex:71: GraphQL.Lang.AST.Visitor.GraphQL.Lang.AST.CompositeVisitor.call_in_order/5
    (graphql) lib/graphql/lang/ast/reducer.ex:33: GraphQL.Lang.AST.Reducer.visit/3
    (graphql) lib/graphql/lang/ast/reducer.ex:21: GraphQL.Lang.AST.Reducer.visit/3
    (graphql) lib/graphql/lang/ast/reducer.ex:51: GraphQL.Lang.AST.Reducer.visit_each_child/3
    (graphql) lib/graphql/lang/ast/reducer.ex:36: GraphQL.Lang.AST.Reducer.visit/3
    (graphql) lib/graphql/lang/ast/reducer.ex:16: GraphQL.Lang.AST.Reducer.reduce/3
    (graphql) lib/graphql/validation/validator.ex:29: GraphQL.Validation.Validator.validate_with_rules/3
    (graphql) lib/graphql.ex:44: GraphQL.execute_with_optional_validation/6
    lib/graphql_relay.ex:28: GraphQL.Relay.introspection/0
    lib/graphql_relay.ex:23: GraphQL.Relay.generate_schema_json!/0
    (stdlib) erl_eval.erl:670: :erl_eval.do_apply/6

I'm not sure whether this is an issue with graphql-elixir or graphql-relay?

EDIT: I get the error when starting the server too, so I don't think it's related to graphql-relay.

[joshprice]

Thanks for the bug report.

Not sure which branch you mean, but please try using the latest GraphQL
release. Also it would be great to see your schema to help debug this.

On Mon, Apr 18, 2016 at 3:19 PM, Ashley Williams notifications@github.com
wrote:

I'm using @markolson https://github.com/markolson's branch with this
fix, however when using graphql-relay, running
GraphQL.Relay.generate_schema_json! throws this error:

[debug] Updating GraphQL schema.json
** (FunctionClauseError) no function clause matching in GraphQL.Type.CompositeType.do_get_fields/1
(graphql) lib/graphql/type/composite_type.ex:33: GraphQL.Type.CompositeType.do_get_fields({:%{}, [], [max_score: {:%{}, [], [type: {:%, [], [{:aliases, [alias: false], [:GraphQL, :Type, :Float]}, {:%{}, [], []}]}, resolve: {:fn, [], [{:->, [], [[{:, [], VideoSchema}, {:, [], VideoSchema}, {:_, [], VideoSchema}], 1]}]}]}, videos: {:%{}, [], [type: {{:., [], [Access, :get]}, [], [{:video_connection, [], VideoSchema}, :connection_type]}, args: {{:., [], [{:aliases, [alias: GraphQL.Relay.Connection], [:Connection]}, :args]}, [], []}, resolve: {:fn, [], [{:->, [], [[{:videos, [], VideoSchema}, {:args, [], VideoSchema}, {:_ctx, [], VideoSchema}], {:block, [], [{{:., [], [{:aliases, [alias: false], [:IO]}, :inspect]}, [], [{:args, [], VideoSchema}]}, {:=, [], [{:cursor_count, [], VideoSchema}, {:try, [], [[do: {{:., [], [{:aliases, [alias: GraphQL.Relay.Connection.List], [:Connection, :List]}, :cursor_to_offset]}, [], [{:||, [context: VideoSchema, imp
ort: Ker
nel], [{{:., [], [Access, :get]}, [], [{:args, [], VideoSchema}, :after]}, {{:., [], [Access, :get]}, [], [{:args, [], VideoSchema}, :before]}]}]}, rescue: [{:->, [], [[{:aliases, [alias: false], [:FunctionClauseError]}], 0]}]]]}]}, {:=, [], [{:count, [], VideoSchema}, {:+, [context: VideoSchema, import: Kernel], [{:+, [context: VideoSchema, import: Kernel], [{:cursor_count, [], VideoSchema}, {{:., [], [Access, :get]}, [], [{:args, [], VideoSchema}, :first]}]}, 1]}]}, {{:., [], [{:aliases, [alias: GraphQL.Relay.Connection.List], [:Connection, :List]}, :resolve]}, [], [{:videos, [], VideoSchema}, {:args, [], VideoSchema}]}]}]}]}]}]})
(graphql) lib/graphql/type/schema.ex:56: GraphQL.Schema.reduce_types/2
(stdlib) lists.erl:1262: :lists.foldl/3
(graphql) lib/graphql/type/schema.ex:57: GraphQL.Schema.reduce_types/2
(stdlib) lists.erl:1262: :lists.foldl/3
(graphql) lib/graphql/type/schema.ex:57: GraphQL.Schema.reduce_types/2
(graphql) lib/graphql/type/schema.ex:31: GraphQL.Schema.reduce_types/1
(graphql) lib/graphql/type/schema.ex:26: GraphQL.Schema.type_from_ast/2
(graphql) lib/graphql/lang/ast/type_info_visitor.ex:100: GraphQL.Lang.AST.Visitor.GraphQL.Lang.AST.TypeInfoVisitor.enter/3
(graphql) lib/graphql/lang/ast/composite_visitor.ex:71: GraphQL.Lang.AST.Visitor.GraphQL.Lang.AST.CompositeVisitor.call_in_order/5
(graphql) lib/graphql/lang/ast/reducer.ex:33: GraphQL.Lang.AST.Reducer.visit/3
(graphql) lib/graphql/lang/ast/reducer.ex:21: GraphQL.Lang.AST.Reducer.visit/3
(graphql) lib/graphql/lang/ast/reducer.ex:51: GraphQL.Lang.AST.Reducer.visit_each_child/3
(graphql) lib/graphql/lang/ast/reducer.ex:36: GraphQL.Lang.AST.Reducer.visit/3
(graphql) lib/graphql/lang/ast/reducer.ex:16: GraphQL.Lang.AST.Reducer.reduce/3
(graphql) lib/graphql/validation/validator.ex:29: GraphQL.Validation.Validator.validate_with_rules/3
(graphql) lib/graphql.ex:44: GraphQL.execute_with_optional_validation/6
lib/graphql_relay.ex:28: GraphQL.Relay.introspection/0
lib/graphql_relay.ex:23: GraphQL.Relay.generate_schema_json!/0
(stdlib) erl_eval.erl:670: :erl_eval.do_apply/6

I'm not sure whether this is an issue with graphql-elixir or graphql-relay
?

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#38 (comment)

[ashleyw]

This is using the master branch. I think this is the relevant schema:

  def node_interface do
    Node.define_interface(fn(obj) ->
      case obj do
        %{videos: _videos} ->
          video_list
        _ ->
          video
      end
    end)
  end

  def video_connection do
   %{
     name: "Video",
     node_type: video,
     edge_fields: %{},
     connection_fields: %{},
     resolve_node: nil,
     resolve_cursor: nil
   } |> Connection.new
  end

  def video do
    %GraphQL.Type.ObjectType{
      name: "Video",
      description: "A Video",
      fields: quote do %{
        id: Node.global_id_field("video"),
        more_like_this: %{
          type: %GraphQL.Type.List{ ofType: video }
          args: %{
            count: %{type: %GraphQL.Type.Int{}}
          },
          resolve: fn _, _, _ -> end
        }
      } end,
      interfaces: [node_interface]
    }
  end

Thanks!