**（RuntimeError）预期的操作/ 2返回一个Plug.Conn，所有插件都必须接收一个连接（conn）并返回一个连接

Question

def create_trans(conn, _params) do

  address = __MODULE__.get_add()
  card = __MODULE__.get_card()

  case Alpha.beta(card, [billing_address: address]) do
    {:ok, result}     -> render conn,"purchase.json",%{purchase: result}
    {:error, reason}  -> render conn,"purchase.json",%{purchase: reason} 
  end

end

The above code gives me the below error, am i missing anything.

** (RuntimeError) expected action/2 to return a Plug.Conn, all plugs must receive a connection (conn) and return a connection

Answer 1

Maybe provide more informations what Alpha.beta/2 should return. Generally your error points that not every scenario is covered in your case block. Consider using as a last scenario _ , which will match the rest.

Also you could simply make this code more readable and DRY if you assign result of the Alpha.beta/2 to the variable and then render the result instead of using case , if you basically do the same in both of these scenarios.

{_, result} = Alpha.beta(card, [billing_address: address)
render(conn, "purchase.json", %{purchase: result}

But in this case you have to be 100% sure that this Alpha.beta/2 returns a tuple, which matches in pattern matching above and according to your issue, it's not so sure.