This will be a project that will use LiveView and ecto to store data for each game that I create. Right off the bat I created an Accounts, Games, Scores ecto table. These at the moment will store:

mix phx.gen.auth Accounts User users
Accounts: User account info, password etc
mix phx.gen.live Games Game games name:text
Games: Names of all the games
mix phx.gen.live Scores Score scores score:integer
Scores: All the scores for a user with key references to Accounts:id, and Games:id

defmodule GameSite.Repo.Migrations.CreateScores do
  use Ecto.Migration

  def change do
    create table(:scores) do
      add :score, :integer
      add :user_id, references(:users, on_delete: :delete_all)
      add :game_id, references(:games, on_delete: :delete_all)

      timestamps(type: :utc_datetime)
    end
  end
end

This should be enough to be sure that I can store Game data. This might need to change later if I find that I'm storing too much or not enough.

We now need to set all the Schema for the tables.
Scores:
defmodule GameSite.Scores.Score do
  use Ecto.Schema
  import Ecto.Changeset

  schema "scores" do
    field :score, :integer
    belongs_to :game, GameSite.Games.Game
    belongs_to :user, GameSite.Accounts.User

    timestamps(type: :utc_datetime)
  end

  @doc false
  def changeset(score, attrs) do
    score
    |> cast(attrs, [:score, :user_id, :game_id])
    |> validate_required([:score, :user_id, :game_id])
    |> foreign_key_constraint(:game_id)
    |> foreign_key_constraint(:user_id)
  end
end

Games:
defmodule GameSite.Games.Game do
  use Ecto.Schema
  import Ecto.Changeset

  schema "games" do
    field :name, :string

    has_many :scores, GameSite.Scores.Score
    timestamps(type: :utc_datetime)
  end

  @doc false
  def changeset(game, attrs) do
    game
    |> cast(attrs, [:name])
    |> validate_required([:name])
  end
end

This will ensure that we set all the relationships as needed. This doesn't however set the needed values for User.id in all the Score Forms. For this to be implemented I need to be sure to mount the current user. To do so we need to add the following to the router.ex for the:

scope "/", GameSiteWeb do
...
    live_session :scores, on_mount: [{GameSiteWeb.UserAuth, :mount_current_user}] do
    #all your routes
    end
end

This allows you to add:
current_user={@current_user} to the 
<.modal ...> at the bottom of all the forms that you will need a user.id for a changeset.

Now that is done we can start to work on a few games.