When we analyzed the User.create_changeset/2 function, we didn't have any validation in place to check whether the username we are storing in the database already exists or not. For a system like ours, this could spell trouble. As such, let's create a unique index on the users table for the username column:
$ cat apps/elixir_drip/priv/repo/migrations/20180320101722_unique_users_constraint.exsdefmodule ElixirDrip.Repo.Migrations.UniqueUsersConstraint do use Ecto.Migration def change do create unique_index(:users, [:username]) endend
After we apply this migration with mix ecto.migrate, the database will start to enforce username uniqueness on any operation on the users table. Let's see what happens if we try to update the xpto_user ...
