Option on_delete: :delete_all raises error instead of deleting errors

Hey there! I’ve got 2 tables with a relationship of one-to-many, and when I try to delete a record from the parent table it raises an error instead of deleting the child records as well.

Here are my table migrations:

create table("user") do
      add(:username, :string, null: false)
      add(:email, :string, null: false)
      add(:password_hash, :string, null: false)
      timestamps()
end

create table("usersession") do
      add(:user_id, references(:user), null: false, on_delete: :delete_all)
      add(:session, :string, null: false)
      timestamps()
end

When trying to run something like Repo.delete(Repo.get!(User, 1)) it just throws a constraint error instead of deleting the record. It’s weird because it feels like this should work and delete all cascading records, right? What am I doing wrong?