Building Database Applications in Elixir with Ecto/

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Approach #2: Use an Abstract Schema

Approach #2: Use an Abstract Schema

Learn how to implement polymorphism in Ecto using separate tables, and one abstract schema.

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Create separate notes tables

This approach might not be entirely intuitive at first glance, but it’s worth exploring as it reveals some interesting features about schemas that we haven’t looked at before. It might also be the right solution for our application.

With this approach, we’ll create separate notes tables for each of the other tables we’re associating with. We’ll have one notes table for artists, another for albums, and so on. Here’s how we might write the migration:

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create table(:notes_for_artists) do 
  add :note, :text, null: false
  add :author, :string, null: false 
  add :assoc_id, references(:artists) 
  timestamps()
end
create table(:notes_for_albums) do 
  add :note, :text, null: false
  add :author, :string, null: false 
  add :assoc_id, references(:albums) 
  timestamps()
end
create table(:notes_for_tracks) do 
  add :note, :text, null: false
  add :author, :string, null: false 
  add :assoc_id, references(:tracks) 
  timestamps()
end

Notice that we used assoc_id for the foreign key. We deliberately chose a more abstract name and used it in each of the tables. We did this so all of the tables have the same column names. This allows us to create a ...