Question about the phoenix.gen.json generator.

question.md

$mix phoenix.new testapi
$cd testapi
$mix ecto.create
$mix phoenix.gen.json User users fullname:string email:string

Add the resource to your api scope in web/router.ex:

resources "/users", UserController, except: [:new, :edit]

under the api block

$mix ecto.migrate
$iex -S mix phoenix.server

In another terminal window:

$curl -H "Content-Type: application/json" -X POST -d '{"user": [{"fullname": "Jeff", "email": "jeff@example.com"}]}'   http://localhost:4000/api/users

Then I get this error in the iex window:

iex(1)> Processing by Testapi.UserController.create/2
  Parameters: %{"user" => [%{"email" => "jeff@example.com", "fullname" => "Jeff"}]}
  Pipelines: [:api]
[info] Sent 500 in 16ms
[error] #PID<0.405.0> running Testapi.Endpoint terminated
Server: localhost:4000 (http)
Request: POST /api/users
** (exit) an exception was raised:
  ** (FunctionClauseError) no function clause matching in Ecto.Changeset.cast/5
    (ecto) lib/ecto/changeset.ex:351: Ecto.Changeset.cast(%Testapi.User{__meta__: #Ecto.Schema.Metadata<:built>, email: nil, fullname: nil, id: nil, inserted_at: nil, updated_at: nil}, %{}, [%{"email" => "jeff@example.com", "fullname" => "Jeff"}], ["fullname", "email"], [])
    (testapi) web/controllers/user_controller.ex:14: Testapi.UserController.create/2
    (testapi) web/controllers/user_controller.ex:1: Testapi.UserController.action/2
    (testapi) web/controllers/user_controller.ex:1: Testapi.UserController.phoenix_controller_pipeline/2
    (testapi) lib/phoenix/router.ex:255: Testapi.Router.dispatch/2
    (testapi) web/router.ex:1: Testapi.Router.do_call/2
    (testapi) lib/testapi/endpoint.ex:1: Testapi.Endpoint.phoenix_pipeline/1
    (testapi) lib/plug/debugger.ex:90: Testapi.Endpoint."call (overridable 3)"/2
    (testapi) lib/phoenix/endpoint/render_errors.ex:34: Testapi.Endpoint.call/2
    (plug) lib/plug/adapters/cowboy/handler.ex:15: Plug.Adapters.Cowboy.Handler.upgrade/4
    (cowboy) src/cowboy_protocol.erl:442: :cowboy_protocol.execute/4

I think this should result in a successful post. What am I missing?

This was very useful to find. Thanks for the follow up!