ChangeSet Ecto.Model all fields of Struct are nil

Question

I'm working on some Phoenix framework and i have encountered a weird problem (as usual). Whenever I try to create some Users, i get User with all fields set to nil. I'm using Mongo.Ecto/

def post_login(conn, %{"login" => login, "password" => password}) do
    # IO.inspect Plug.Conn.read_body(conn)
    a = User.changeset(%User{}, %{"login" => "login", "password" => "password"})
    IO.inspect a
    Repo.insert( a )
    redirect conn, to: "/default"
end

And the model:

defmodule HelloWorld.User do
  use HelloWorld.Web, :model

  @primary_key {:id, :binary_id, autogenerate: true}
  schema "users" do
    field :login, :string
    field :password, :string
  end


  @required_fields ~w()
  @optional_fields ~w()
  def changeset(model, params \\ :empty) do
    model
    |> cast(params, @required_fields, @optional_fields)
  end
end

And the screen from console:

As you can see in the picture, both login and password fields are nils which makes me feel I've done something incredibly stupid.

Answer 1

The fields need to exist in the options to the cast/4 function:

  @required_fields ~w()
  @optional_fields ~w(login password)
  def changeset(model, params \\ :empty) do
    model
    |> cast(params, @required_fields, @optional_fields)
  end

Anything that is in required_fields but not in the params will add an error to that field on the changeset. If you want the fields to be required just move them to the required_fields list.