Hi all, new to Elixir, going through the “Programming Phoenix LiveView” book right now. Fairly new to working with Ecto as well

An exercise in chapter instructs the reader to add a username field to the User struct, and implement the Ecto migrations to support that.

Additionally, I would like to make the username:

• mandatory
• unique
• populate email as default value for existing DB records.

I’ve achieved it successfully with the following migrations:

First migration: create column:

  def change do
    alter(table(:users)) do
      add :username, :citext
    end
  end

Second migration, fill column and make it unique/mandatory:

  def change do
    from(u in Pento.Accounts.User, update: [set: [username: u.email]])
    |> Pento.Repo.update_all([])

    alter(table(:users)) do
      modify :username, :citext, null: false
    end

    create(unique_index(:users, :username))
  end

However, I can’t seem to be able to make these updates as a single migration. Why?

My first draft looked like this:

defmodule Pento.Repo.Migrations.CreateUsernameColumn do
  use Ecto.Migration
  import Ecto.Query, only: [from: 2]

  def change do
    alter(table(:users)) do
      add :username, :citext
    end

    from(u in Pento.Accounts.User, update: [set: [username: u.email]])
    |> Pento.Repo.update_all([])

    alter(table(:users)) do
      modify :username, :citext, null: false
    end

    create(unique_index(:users, :username))
  end
end

… but it throws an error in the from(u in... statement as Users doesn’t have the column called username. But I just created that column 2 rows above. What am I missing?

P.S. If it helps, complete repo here: Ch2/add username field by iarekk · Pull Request #7 · iarekk/programming_phoenix_liveview · GitHub