EctoEnum

EctoEnum is an Ecto extension to support enums in your Ecto models.

Usage

First, we add ecto_enum to mix.exs:

def deps do
  [{:ecto_enum, "~> 1.0"}]
end

We will then have to define our enum. We can do this in a separate file since defining an enum is just defining a module. We do it like:

# lib/my_app/ecto_enums.ex

import EctoEnum
defenum StatusEnum, registered: 0, active: 1, inactive: 2, archived: 3

Once defined, EctoEnum can be used like any other Ecto.Type by passing it to a field in your model's schema block. For example:

defmodule User do
  use Ecto.Model

  schema "users" do
    field :status, StatusEnum
  end
end

In the above example, the :status will behave like an enum and will allow you to pass an integer, atom or string to it. This applies to saving the model, invoking Ecto.Changeset.cast/4, or performing a query on the status field. Let's do a few examples:

iex> user = Repo.insert!(%User{status: 0})
iex> Repo.get(User, user.id).status
:registered

iex> %{changes: changes} = cast(%User{}, %{"status" => "active"}, ~w(status), [])
iex> changes.status
:active

iex> from(u in User, where: u.status == ^:registered) |> Repo.all() |> length
1

Passing a value that the custom Enum type does not recognize will result in an error.

Reflection

The enum type StatusEnum will also have a reflection function for inspecting the enum map in runtime.

iex> StatusEnum.__enum_map__()
[registered: 0, active: 1, inactive: 2, archived: 3]
iex> StatusEnum.__valid_values__()
[0, 1, 2, 3, :registered, :active, :inactive, :archived, "active", "archived",
"inactive", "registered"]

Using Postgres's Enum Type

Enumerated Types in Postgres are now supported. To use Postgres's Enum Type with EctoEnum, use the defenum/3 macro instead of defenum/2. We do it like:

# lib/my_app/ecto_enums.ex

import EctoEnum
defenum StatusEnum, :status, [:registered, :active, :inactive, :archived]

The second argument is the name you want used for the new type you are creating in Postgres. Note that defenum/3 expects a list of atoms(could be strings) instead of a keyword list unlike in defenum/2. Another notable difference is that you can no longer use integers in place of atoms or strings as values in your enum type. Given the above code, this means that you can only pass the following values:

[:registered, :active, :inactive, :archived, "registered", "active", "inactive", "archived"]

In your migrations, you can make use of helper functions like:

def up do
  StatusEnum.create_type
  create table(:users_pg) do
    add :status, :status
  end
end

def down do
  drop table(:users_pg)
  StatusEnum.drop_type
end

create_type/0 and drop_type/0 are automatically defined for you in your custom Enum module.

Important notes/gotchas

Postgres

Keep in mind that ALTER TYPE ... ADD VALUE cannot be executed inside a transaction block. This means that running this inside a migration requires you to set to the module attribute @disable_ddl_transaction to true. For example:

defmodule MyApp.Repo.Migrations.AddToGenderEnum do
  use Ecto.Migration
  @disable_ddl_transaction true
  
  def up do
    Ecto.Migration.execute "ALTER TYPE gender ADD VALUE 'other'"
  end

  def down do
  end
end

Note that there is no easy way to drop an enum value. It is not supported and you must create a new type without the value. Here are some work-arounds. Best to avoid having to drop an enum value.