Ecto Migration

20161204173835_create_video.exs

defmodule Rumbl.Repo.Migrations.CreateVideo do
  use Ecto.Migration

  def change do
    create table(:videos) do
      add :url, :string
      add :title, :string
      add :description, :text
      add :user_id, references(:users, on_delete: :nothing)

      timestamps()
    end
    create index(:videos, [:user_id])

  end
end

20161204183835.exs

def up do
  alter table(:videos) do
    modify :user_id, references(:users, on_delete: :delete_all)
  end
end

20161217183938_change_user_id_from_videos.exs

defmodule Rumbl.Repo.Migrations.ChangeUserIdFromVideos do
  use Ecto.Migration

  def up do
    execute "ALTER TABLE videos DROP CONSTRAINT videos_user_id_fkey"

    alter table(:videos) do
      modify :user_id, references(:users, on_delete: :delete_all)
    end
  end

  def down do
    execute "ALTER TABLE videos DROP CONSTRAINT videos_user_id_fkey"

    alter table(:videos) do
      modify :user_id, references(:users, on_delete: :nothing)
    end
  end
end

gistfile1.txt

18:32:30.821 [info]  alter table videos
** (Postgrex.Error) ERROR (duplicate_object): constraint "videos_user_id_fkey" for relation "videos" already exists