How to handle Ecto associations with UUIDs

Overriding default database configurations can be tricky business and that’s no exception when trying to go from using id for primary keys to using UUID. In a previous post I went over how to set different primary keys in Ecto, which setup our app to use UUID’s at the database level.

Now we’ll be working to make this function at the app level, and it only requires a few changes to our schema files. This example will use a standard has_many and belongs_to association, piggy backing off of the previously mentioned post.

In both the has_many and belongs_to side of the association the setup is going to look the same. It takes the format of association_function: :ecto_schema, EctoSchemaModule, references :field_name.

For the has many side that looks like this:

defmodule Barks.Organization do
  use Ecto.Schema
  alias Barks.Team

  @primary_key {:uuid, :binary_id, autogenerate: true}
  @foreign_key_type :binary_id
  schema "organizations" do
    field :name, :string
    has_many :teams, Team, references: :uuid
  end
end

And for the belongs_to side of the assocation that looks like:

defmodule Barks.Team do
  use Ecto.Schema
  alias Barks.Organization

  @primary_key {:uuid, :binary_id, autogenerate: true}
  @foreign_key_type :binary_id
  schema "teams" do
    field :name, :string
    belongs_to :organization, Organization, references: :uuid
  end
end