Associates params schemas with supported callbacks and casts received values.

Place @params_schema immediately before a supported callback to call parse/1 before entering its body. A module schema binds a struct to the callback's params, while a map schema definition binds a map.

use ExParamsSchema.Handler

@params_schema Params.Update
def handle_event("update", params, socket) do
  params.id
  {:noreply, socket}
end

Supported callbacks

@params_schema can be specified only for public handle_event/3, handle_params/3, and handle_info/2 callbacks. Bind the second argument of handle_event/3 and the first argument of handle_params/3 to variables. Bind the tuple payload of handle_info/2 to a variable named params.

@params_schema Params.RecordUpdate
def handle_info({:record_update, params}, socket) do
  params.id
  {:noreply, socket}
end

Callback clauses without the annotation are not transformed.

Error handling

To handle parse errors, specify an error handler for the module.

use ExParamsSchema.Handler,
  on_error: :handle_params_error

The error handler is called as handler(source, reason, socket). For handle_event/3, source is the event name; for handle_params/3 and handle_info/2, it is the params before casting. The handler must return a value appropriate for the callback, usually {:noreply, socket}.

When on_error: is omitted, parse errors return {:noreply, socket}.

Compile-time errors

Specifying @params_schema on an unsupported function, a private function, or an unsupported callback arity raises ArgumentError. It also raises ArgumentError when the params to be cast are not bound to variables, or when the handle_info/2 payload is not bound to params.