Using cast/3 with @optional_fields and @required_fields for simplicity

bar.ex

defmodule Splife.Bar do
  use Splife.Web, :model

  schema "bars" do
    field :baz, :string
    field :fizz, :string

    timestamps()
  end

  @required_fields ~w(baz)a
  @optional_fields ~w(fizz)a

  def changeset(struct, params \\ %{}) do
    struct
    |> cast(params, @required_fields ++ @optional_fields)
    |> validate_required(@required_fields)
  end
end