Programming Ecto

Approach #3: Using many_to_many

The final approach for creating polymorphic associations is to use many_to_many. With this approach, we create a single notes table, then add separate join tables for each of the different associations we want to use with notes. We would set this up the same way we did back in ​Many-to-Many Associations​.

First, we add a migration to create a single notes table:

priv/repo/migrations/20180620125250_add_notes_tables.exs

create table(:notes_with_joins) do
  add :note, :text, null: false
  add :author, :string, null: false
  timestamps()
end

And also add migrations to create the join tables:

priv/repo/migrations/20180815192832_add_notes_join_tables.exs

create table( ...