UUID Fields in Phoenix

Phoenix is still a young framework. As such, you may encounter problems that no one else has or problems that are just slightly different than others. This is a story of the latter.

I have a model that I want to have a UUID as its id. After a little searching, I came across this StackOverflow post. It's great—worked for me the first time. Until I added other models.

The changes you make to web.ex in this solution force all models to have UUIDs as ids. It took me a while to realize that the solution to my specific problem was to move those edits to web.ex into my model, but when I did that I kept getting validation errors about my UUID not being an integer. After spending a bunch of time looking into source code and chatting on IRC, I realized that I was looking at an ordering problem: the definitions of the id field need to come before the schema block.

defmodule MyApp.MyModel
  use MyApp.Web, :model

  # The following needs to be before the schema declaration
  # to properly take effect
  @primary_key {:id, Ecto.UUID, read_after_writes: true}
  @foreign_key_type Ecto.UUID

  schema "my_models" do
    ...
  end
end

And there you have it. I also left out the before_insert MyApp.UUID, :put_uuid, [] part, which just has the database generate the UUID for me, as it does integer ids.

As José says in the SO post, working with UUIDs is likely to be improved in the future. This is echoed somewhat in Chris McCord's keynote where he mentions that token auth for channels is a feature they're looking to add in the future. (I'm using UUIDs as tokens for auth in my application.)

Published on May 15, 2015