How to validate that at least 2 variable fields in a form are filled

one way would be to Enum.filter to return true for all the fields that are present? and then check that the length or count is larger than 2..

eg

Enum.filter(fields, &present?(changeset, &1)) |> length > 2

or 

Enum.filter(fields, &present?(changeset, &1)) |> Enum.count > 2

I would be very careful to call the validation with the specific fields |> validate_required_inclusion([:title , :content]) - say you add a checkbox in the future and you don’t want code to break or unexpected behaviour as that checkbox all of a sudden counts in this validation..

def validate_required_inclusion(changeset, fields) do
  if Enum.filter(fields, &present?(changeset, &1)) |> length > 2 do
    changeset
  else
    # Add the error to the first field only since Ecto requires a field name for each error.
    add_error(changeset, hd(fields), "Two of these fields must be present: #{inspect fields}")
  end
end

def present?(changeset, field) do
  value = get_field(changeset, field)
  value && value != ""
end

Thanks, this works great!