Prevent operation from casting map keys to symbols

[LukasKnuth]

I'm using the operator macro in my Controller to define the request_body I'm expecting users to provide. That body uses a module and the OpenApiSpex.schema helper macro.

# in my controller
operation :create, request_body: {"MyBody", "application/json", MyBodyParams}

def create(%{body_params: params}, _) do
  Persistence.save_data(params)
end

# Somewhere else
defmodule MyBodyParams do
    require OpenApiSpex

    OpenApiSpex.schema(%{
      type: :object,
      properties: %{
        id: %Schema{...}
      }
    })
end

Now in my test, I have observed the following issue:

post(conn, Routes.end_point(conn, :create), %{
  "id" => "abc-123",
  "other" => "something"
})

# This is what reaches Persistence.save_data/1
%{
  :id => "abc-123",
  "other" => "something"
}

So as far as I can tell, all known body parameters are changed to have symbol keys, while the unknown parameters remain string keys (as given by Plug).

This causes problems when passing this to Ecto.Changeset.cast:

 ** (Ecto.CastError) expected params to be a map with atoms or string keys, got a map with mixed keys: ...

Can I deactivate this behavior? I haven't been able to find documentation on it. I tried the struct?: false option, but that doesn't seem to change anything.

[zorbash]

@LukasKnuth What is the desired behaviour in your case? Would you prefer the library to omit the undocumented attributes or to not atomise keys?

[LukasKnuth]

I'd prefer it giving me the option to not atomize keys.

Although I now understand that that is intended behavior to tell specified properties and additionalProperties apart.

I think this could be implemented by adding an additional cast_opt option like atomize? to OpenApiSpex.Cast.cast/4, and then supporting this in the Plug.

[LukasKnuth]

I've since dug into the source code of the library and found some answers:

• The OpenApiSpex.CastAndValidate Plug starts the validation based on the operation declarations in the controller.
• There is an option to this plug replace_params where no parameters are replaced. This however does not help because then, e.g. DateTimes are no longer parsed.
• The atomization of keys is documented in OpenApiSpex.Cast.cast/4, where it states:

For an :object schema type, the cast operation returns a map with atom keys.

There is AFAIK no way to configure or prevent this behavior. I have now solved it by specifically setting additionalProperties: false in my schema.