Phoenix: changeset does not take into account changes on foreign keys - phoenix-framework

Question

I am trying to update values for a record in the console ies -S mix .
iex> video = Repo.one(from v in Video, limit: 1)
%Rumbl.Video{...}
if I change the title of the video, everything seems to be working correctly.
iex> changeset = Video.changeset(video, %{title: "some title"})
#Ecto.Changeset<action: nil, changes: %{title: "some title"},
errors: [], data: #Rumbl.Video<>, valid?: true>
But changing a foreign key seems to have no effect:
iex> changeset = Video.changeset(video, %{category_id: 3})
#Ecto.Changeset<action: nil, changes: %{},
errors: [], data: #Rumbl.Video<>, valid?: true>
What should I do to for the changes on the foreign key to be taken into accoung ?
Here is the model
defmodule Rumbl.Video do
use Rumbl.Web, :model
schema "videos" do
field :url, :string
field :title, :string
field :description, :string
belongs_to :user, Rumbl.User, foreign_key: :user_id
belongs_to :category, Rumbl.Category, foreign_key: :category_id
timestamps()
end
#required_fields ~w(url title description)
#optional_fields ~w(category_id)
#doc """
Builds a changeset based on the `struct` and `params`.
"""
def changeset(struct, params \\ %{}) do
struct
|> cast(params, #required_fields, #optional_fields)
|> validate_required([:url, :title, :description])
|> assoc_constraint(:category)
end
end

Answer 1

In Ecto 2.2, the fourth argument to cast is opts, not optional fields. It used to be optional fields earlier which was deprecated in v2.1 with a recommendation to use validate_required instead. This was apparently removed in v2.2.0 although I can't find it in the changelog. You should change your code to this for Ecto 2.2:
struct
|> cast(params, #required_fields ++ #optional_fields)
|> validate_required([:url, :title, :description])
or do this:
#required_fields ~w(url title description)a
#optional_fields ~w(category_id)a
and
|> cast(params, #required_fields ++ #optional_fields)
|> validate_required(#required_fields)