(FunctionClauseError) no function clause matching in JSONAPI.Utils.DataToParams.transform_relationship/2

[matt-glover]

The error in the title occurs if certain keys are present and others are missing from the JSON body when attempting to POST to an endpoint.

In my local example I setup a plug pipeline with the following JSON API plugs:

    plug JSONAPI.EnsureSpec
    plug JSONAPI.Deserializer

I largely copied over the examples from the README to setup some views and wire those into a controller.

Once I called the route via curl I correctly got warnings from EnsureSpec for many different missing JSON keys.
Example:

{"errors":[{"detail":"Check out http://jsonapi.org/format/#crud for more info.","source":{"pointer":"/data/type"},"status":"400","title":"Missing type in data parameter"}]}

Once I partially/incorrectly defined a relationship the deserializer started to crash leading to a 500 error:

[info] POST /posts
[debug] Processing with TryJsonWeb.PageController.create/2
  Parameters: %{"data" => %{"attributes" => %{}, "type" => "posts"}, "relationships" => %{"comment" => %{"data" => %{}}}}
  Pipelines: [:jsonapi]
[info] Sent 500 in 6ms
[error] #PID<0.846.0> running TryJsonWeb.Endpoint (connection #PID<0.845.0>, stream id 1) terminated
Server: localhost:4000 (http)
Request: POST /posts
** (exit) an exception was raised:
    ** (FunctionClauseError) no function clause matching in JSONAPI.Utils.DataToParams.transform_relationship/2
        (jsonapi 1.5.1) lib/jsonapi/utils/data_to_params.ex:60: JSONAPI.Utils.DataToParams.transform_relationship({"comment", %{"data" => %{}}}, %{})
        (stdlib 3.17) maps.erl:410: :maps.fold_1/3
        (jsonapi 1.5.1) lib/jsonapi/utils/data_to_params.ex:53: JSONAPI.Utils.DataToParams.process_relationships/1
        (jsonapi 1.5.1) lib/jsonapi/utils/data_to_params.ex:15: JSONAPI.Utils.DataToParams.process/1
        (jsonapi 1.5.1) lib/jsonapi/plugs/deserializer.ex:61: JSONAPI.Deserializer.call/2
        (try_json 0.1.0) TryJsonWeb.Router.jsonapi/2
        (try_json 0.1.0) lib/try_json_web/router.ex:1: TryJsonWeb.Router.__pipe_through1__/1
        (phoenix 1.6.16) lib/phoenix/router.ex:346: Phoenix.Router.__call__/2
        (try_json 0.1.0) lib/try_json_web/endpoint.ex:1: TryJsonWeb.Endpoint.plug_builder_call/2
        (try_json 0.1.0) lib/plug/debugger.ex:136: TryJsonWeb.Endpoint."call (overridable 3)"/2
        (try_json 0.1.0) lib/try_json_web/endpoint.ex:1: TryJsonWeb.Endpoint.call/2
        (phoenix 1.6.16) lib/phoenix/endpoint/cowboy2_handler.ex:54: Phoenix.Endpoint.Cowboy2Handler.init/4
        (cowboy 2.10.0) /home/matt/code/try_json/deps/cowboy/src/cowboy_handler.erl:37: :cowboy_handler.execute/2
        (cowboy 2.10.0) /home/matt/code/try_json/deps/cowboy/src/cowboy_stream_h.erl:306: :cowboy_stream_h.execute/3
        (cowboy 2.10.0) /home/matt/code/try_json/deps/cowboy/src/cowboy_stream_h.erl:295: :cowboy_stream_h.request_process/3
        (stdlib 3.17) proc_lib.erl:226: :proc_lib.init_p_do_apply/3

I'm happy to offer a PR to the deserializer flow to reduce the cases that crash in the face of malformed params like these. But I wanted to log an issue in case there's a preference for an alternate approach with this project like adding more EnsureSpec checks or something else.

[mattpolzin]

I think I like your idea of handling this with EnsureSpec as opposed to making other code handle more cases not representable by JSON:API. A tough call, but that's the way I think I lean.

[matt-glover]

Cool. I'll take a pass at enhancing the spec flow early next week and share what I come up with.

[mattpolzin]

Closed by #299