Simplify data model

Artists can be embedded inside records - given the projected size of the
dataset (a few 1000s in the worst case) relationships can be built in
memory without the need to be denormalized into separate tables.

lib/music_library/records.ex

@@ -37,15 +37,7 @@ defmodule MusicLibrary.Records do
       ** (Ecto.NoResultsError)
 
   """
-  def get_record!(id) do
-    q =
-      from r in Record,
-        left_join: a in assoc(r, :artists),
-        preload: [artists: a],
-        where: r.id == ^id
-
-    Repo.one!(q)
-  end
+  def get_record!(id), do: Repo.get!(Record, id)
 
   @doc """
   Creates a record.

lib/music_library/records/artist.ex

@@ -1,25 +0,0 @@
-defmodule MusicLibrary.Records.Artist do
-  use Ecto.Schema
-  import Ecto.Changeset
-
-  alias MusicLibrary.{Records.ArtistRecord, Records.Record}
-
-  @primary_key {:id, :binary_id, autogenerate: true}
-  @foreign_key_type :binary_id
-  schema "artists" do
-    field :name, :string
-    field :image, :string
-    field :musicbrainz_id, Ecto.UUID
-
-    many_to_many :records, Record, join_through: ArtistRecord
-
-    timestamps(type: :utc_datetime)
-  end
-
-  @doc false
-  def changeset(artist, attrs) do
-    artist
-    |> cast(attrs, [:name, :musicbrainz_id, :image])
-    |> validate_required([:name, :musicbrainz_id, :image])
-  end
-end

lib/music_library/records/artist_record.ex

@@ -1,20 +0,0 @@
-defmodule MusicLibrary.Records.ArtistRecord do
-  use Ecto.Schema
-  import Ecto.Changeset
-
-  @primary_key {:id, :binary_id, autogenerate: true}
-  @foreign_key_type :binary_id
-  schema "artists_records" do
-    field :artist_id, :binary_id
-    field :record_id, :binary_id
-
-    timestamps(type: :utc_datetime)
-  end
-
-  @doc false
-  def changeset(artist_record, attrs) do
-    artist_record
-    |> cast(attrs, [])
-    |> validate_required([])
-  end
-end

lib/music_library/records/record.ex

@@ -2,8 +2,6 @@ defmodule MusicLibrary.Records.Record do
   use Ecto.Schema
   import Ecto.Changeset
 
-  alias MusicLibrary.{Records.Artist, Records.ArtistRecord}
-
   @primary_key {:id, :binary_id, autogenerate: true}
   @foreign_key_type :binary_id
   schema "records" do
@@ -14,7 +12,10 @@ defmodule MusicLibrary.Records.Record do
     field :musicbrainz_id, Ecto.UUID
     field :genres, {:array, :string}
 
-    many_to_many :artists, Artist, join_through: ArtistRecord
+    embeds_many :artists, Artist do
+      field :name, :string
+      field :musicbrainz_id, Ecto.UUID
+    end
 
     timestamps(type: :utc_datetime)
   end
@@ -25,4 +26,10 @@ defmodule MusicLibrary.Records.Record do
     |> cast(attrs, [:type, :title, :musicbrainz_id, :year, :genres, :image])
     |> validate_required([:type, :title, :musicbrainz_id, :year, :genres, :image])
   end
+
+  def add_artists(record, artists_attrs) do
+    record
+    |> change()
+    |> put_embed(:artists, artists_attrs)
+  end
 end