Phoenix.NotAcceptableError - How can I return an error instead of having the app just have an exception?

idi527 · December 12, 2017, 8:36pm

There is a way to specify http status code and plug will intercept the exception and show the error message with the specified status code or something like that. That’s how ecto exceptions work in phoenix.

github.com

phoenixframework/phoenix_ecto/blob/master/lib/phoenix_ecto/plug.ex

errors = [
  {Ecto.CastError, 400},
  {Ecto.Query.CastError, 400},
  {Ecto.NoResultsError, 404},
  {Ecto.StaleEntryError, 409},
  {Ecto.InvalidChangesetError, 422}
]

excluded_exceptions = Application.get_env(:phoenix_ecto, :exclude_ecto_exceptions_from_plug, [])

for {exception, status_code} <- errors do
  unless exception in excluded_exceptions do
    defimpl Plug.Exception, for: exception do
      def status(_), do: unquote(status_code)
    end
  end
end

unless Ecto.SubQueryError in excluded_exceptions do
  defimpl Plug.Exception, for: Ecto.SubQueryError do

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So, you either need to define an implementation for the exception

defimpl Plug.Exception, for: Your.Error do
  def status(_exception), do: 400 # or anything else
end

or have a :plug_status field in the exception.

defmodule Your.Error do
  defexception [message: "...", plug_status: 400]
end

More on this: http://joshwlewis.com/essays/elixir-error-handling-with-plug/