How do you ensure a unique index when the user tries to get more than one ticket for a paid conference? And the user gets multiple tickets for a free conference?
What are our goals here?
- sent paid conference to
Ticket.changeset/1to ensure thestatus: :paid, create one. - sent free conference to
Ticket.changeset/1to ensure thestatus: :free, create many.
How can we apply these to our business logic:
create table(:tickets) do
add :conference_id, references(:conferences), null: false
add :user_id, references(:users), null: false
add :status, :string, null: false, default: "free"
end
create unique_index(:tickets, [:conference_id, :user_id, :status], where: "status = 'paid'")
Now, how can we test?
iex> Ticket.changeset(%{conference: %{is_paid: false}, user: %{...}, status: :free}) |> Repo.insert()
[debug] QUERY OK
{:ok,
%Ticket%{id: 1, status: :free, conference_id: 1, user_id: 1}
}
iex> Ticket.changeset(%{conference: %{is_paid: false}, user: %{...}, status: :free}) |> Repo.insert()
[debug] QUERY OK
{:ok,
%Ticket%{id: 2, status: :free, conference_id: 1, user_id: 1}
}
iex> Ticket.changeset(%{conference: %{is_paid: true}, user: %{...}, status: :paid}) |> Repo.insert()
[debug] QUERY OK
{:ok,
%Ticket%{id: 3, status: :paid, conference_id: 2, user_id: 1}
}
iex> Ticket.changeset(%{conference: %{is_paid: true}, user: %{...}, status: :paid}) |> Repo.insert()
[debug] QUERY ERROR
** (Ecto.ConstraintError)
Awesome!
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