Programming Phoenix

Managing Registration Changesets

You’ve already seen a changeset for creating a new user—the one that handles the name and username. Let’s review that now:

authentication/rumbl/web/models/user.ex

def changeset(model, params \\ :empty) do
  model
  |> cast(params, ~w(name username), [])
  |> validate_length(:username, min: 1, max: 20)
end

The Ecto.Changeset.cast function converts that naked map to a changeset and, for security purposes, limits the inbound parameters to the ones you specify. Then, we fire a validation limiting the length of valid usernames to one to twenty characters. Remember, we need to supply :empty parameters instead of an empty map so Ecto can distinguish our blank new changeset from an empty form submission ...