For this post I wanted to go over the way you can add in a new column for a table, specifically for adding in a User Name for the authorization table in my Game Site. First and foremost you must use the command line to create a new migration (you could always manually do this but start here).

mix ecto.gen.migration the_name_for_the_migration_or_what_it_does

This will create a timestamped file under priv/repo/migrations.

Within this file you could add another table (create table(:name)) or in this case we will alter a table with the following:

def change do
  alter table(:users) do
    add :user_name, :string, null: false
  end
end

Once this is done we need to alter the schema for the table:

schema "users" do
  ...
  field :user_name, :string
  ...
end

Then we need to be sure that we cast the information as well as be sure that the name is not taken:

def registration_changeset(user, attrs, opts \\ []) do
  user
  |> cast(attrs, [:email, :password, :user_name]) # be sure to add in :user_name
  ...
  |> unsafe_validate_unique(:user_name, Blog.Repo)
  |> unique_constraint(:user_name, message: "Name taken")
end

The last two lines will make sure that you are not adding in a used name. The first of the two will allow the changeset to check the database for the name.

We now need to change the user creation page and allow for the new field:

<.simple_form
  for={@form}
  id="registration_form"
  phx-submit="save"
  phx-change="validate"
  phx-trigger-action={@trigger_submit}
  action={~p"/users/log_in?_action=registered"}
  method="post"
>
  ...
  <.input field={@form[:email]} type="email" label="Email" required />
  <.input field={@form[:password]} type="password" label="Password" required />
  <.input field={@form[:user_name]} type="text" label="User Name" required />
  ...
</.simple_form>

The last line is the new field.

So long as you have all the correct settings from above, you should have a new column for your User database.