EDIT ** The code now works after some help

I started a thread a few days ago with some general questions and since I am now focused and have some running code I thought it would make sense to post fresh with more direct questions.

I have Users which can have friendships and the converse of that is a reverse_friendship using the Friendships table (many_to_many relationships). My attempted code is below but I am having 2 problems.

1. how to add the associations with timestamps. If I don’t add timestamps to the table in the Friendship migration the inserts run fine
2. put_assoc works (User 1 has User 2 as a friend and User 2 has User 1 as a reverse friend). However when I go to add another I get a warning about on_replace, I think thats because put_assoc is essentially trying to overwrite the entire friends/reverse friends. How can I add friend/reverse_friend associations and have it be additive (Add User 2 then User 3, etc to User 1 as a friend).

User Schema

defmodule App.Users.User do
  use Ecto.Schema
  import Ecto.Changeset

  schema "users" do
    field :name, :string
    field :phone_number, :string
    field :username, :string
    field :email, :string, null: false
 
    many_to_many :friends, User,
      join_through: "friendships",
      join_keys: [from_user_id: :id, to_user_id: :id]

    many_to_many :reverse_friends, User,
      join_through: "friendships",
      join_keys: [to_user_id: :id, from_user_id: :id]

    timestamps()
  end

  @doc false
  def changeset(user_or_changeset, attrs) do
    required_fields = [:username, :name, :email, :phone_number]

    user_or_changeset
    |> cast(attrs, required_fields)
    |> validate_required(required_fields)
  end

end

User Migration

defmodule App.Repo.Migrations.CreateUsers do
  use Ecto.Migration

  def change do
    create table(:users) do
      add :name, :string, null: false
      add :username, :string, null: false
      add :email, :string, null: false
      add :phone_number, :string, null: false

      timestamps()
    end

    create unique_index(:users, [:username, :email, :phone_number])
  end
end

Friendship Schema

defmodule App.Users.Friendship do
  use Ecto.Schema
  alias App.Users.User
  import Ecto.Changeset

  @primary_key false
  schema "friendships" do
    belongs_to :from_user, User
    belongs_to :to_user, User

    timestamps()
  end

end

Friendship Migration

defmodule App.Repo.Migrations.AddCreateFriendshipTable do
  use Ecto.Migration

  def change do
    create table(:friendships, primary_key: false) do
      add :from_user_id, references(:users)
      add :to_user_id, references(:users)
      add :accepted, :boolean, default: false

      timestamps()
    end

    create unique_index(:friendships, [:from_user_id, :to_user_id])
  end
end

Users Context Module

defmodule App.Users do
  import Ecto.Query, warn: false
  alias App.Repo
  alias App.Users.User
  alias App.Users.Friendship

  def add_friend(user, friend_user) do
      %Friendship{}
      |> change()
      |> put_assoc(:from_user, user)
      |> put_assoc(:to_user, friend_user)
      |> Repo.insert()
  end

end