Ecto validate_required of either of two attributes

Question

What's the best way to do a validation of the presence of either of two attributes for a changeset?

The validation should only fail if neither of the two attributes is provided

e.g. consider a User model with attributes :name, :uid, :email, :phone

• :name always needs to be present
• either :email or :uid should be present
• :phone is optional

Would this work?

  def changeset(struct, params \\ %{}) do
    struct
      |> cast(params, [:name,:email,:uid,:phone])
      |> validate_required([:name, :email]) || validate_required([:name, :uid]
    end
  end

Answer 1

You may start with something like:

def changeset(struct, params \\ %{}) do
  struct
    |> cast(params, ~w(name email uid phone)a)
    |> validate_required(:name)
    |> validate_required_params(params)
  end
end

def validate_required_params(changeset, %{"uid" => _}) do
  changeset
  |> validate_required(:uid)
end

def validate_required_params(changeset, %{"email" => _}) do
  changeset
  |> validate_required(:email)
end

def validate_required_params(changeset, _params) do
  changeset
  |> add_error(:params, "either :uid or :email is required")
end

But you need to also check for example if both uid and email are provided. What in such case?