Hi ,
I am trying to save data from an appointment form in which there is a many-to-many relationship (one appointment can have many services and one service can have many appointments), in the appointment form I can select several services and I want to store the services selected in the database with the many-to-many relationship.

Here is my schema of the appointments:

defmodule MedussaStudio.Appointments.Appointment do
  alias MedussaStudio.AppointmentsServices.AppointmentService
  alias MedussaStudio.Accounts
  use Ecto.Schema
  import Ecto.Changeset

  schema "appointments" do
    field :date, :date
    field :start_time, :time
    field :end_time, :time
    belongs_to :user, Accounts.User
    many_to_many :appointment_services, MedussaStudio.Services.Service,
      join_through: AppointmentService,
      on_replace: :delete

    timestamps(type: :utc_datetime)
  end

  @doc false
  def changeset(appointment, attrs) do
    appointment
    |> cast(attrs, [:date, :start_time, :end_time, :user_id])
    |> validate_required([:date, :start_time, :end_time])
  end
end

Here is my schema of the services:

defmodule MedussaStudio.Services.Service do
  alias MedussaStudio.AppointmentsServices.AppointmentService
  use Ecto.Schema
  import Ecto.Changeset

  schema "services" do
    field :name, :string
    field :price, :decimal

    many_to_many :appointment_services, MedussaStudio.Appointments.Appointment,
      join_through: AppointmentService,
      on_replace: :delete

    timestamps(type: :utc_datetime)
  end

  @doc false
  def changeset(service, attrs) do
    service
    |> cast(attrs, [:name, :price])
    |> validate_required([:name, :price])
  end
end

And here is the function of my live view that saves the appointments:

  defp save_appointment(socket, :new, appointment_params) do
    case Appointments.create_appointment(add_user_id_to_appointment(socket, appointment_params)) do
      {:ok, appointment} ->
        %{"services" => services} = appointment_params

        id_services =
          Enum.map(services, fn service ->
            service |> String.to_integer() |> Services.get_service!()
          end)

        updated_appointment =
          appointment
          |> Repo.preload(:appointment_services)
          |> Ecto.Changeset.change()
          |> Ecto.Changeset.put_assoc(
            :appointment_services,
            id_services
          )
          |> Repo.update()

        case updated_appointment do
          {:ok, appointment} ->
            notify_parent({:saved, appointment})

            {:noreply,
             socket
             |> put_flash(:info, "Cita creada exitosamente")
             |> push_patch(to: socket.assigns.patch)}

          {:error, %Ecto.Changeset{} = changeset} ->
            {:noreply, assign_form(socket, changeset)}
        end

      {:error, %Ecto.Changeset{} = changeset} ->
        {:noreply, assign_form(socket, changeset)}
    end
  end

This is my schema of appointment services that saves the association:

defmodule MedussaStudio.AppointmentsServices.AppointmentService do
  use Ecto.Schema

  schema "appointments_services" do
    belongs_to :service, MedussaStudio.Services.Service
    belongs_to :appointment, MedussaStudio.Appointments.Appointment

    timestamps()
  end
end

And this is my error when i try to save the appointment with the appointment form data

[error] GenServer #PID<0.6405.0> terminating
** (Postgrex.Error) ERROR 42703 (undefined_column) column "id" does not exist

    query: INSERT INTO "appointments_services" ("appointment_id","service_id","inserted_at","updated_at") VALUES ($1,$2,$3,$4) RETURNING "id"
    (ecto_sql 3.11.1) lib/ecto/adapters/sql.ex:1054: Ecto.Adapters.SQL.raise_sql_call_error/1
    (ecto 3.11.1) lib/ecto/repo/schema.ex:775: Ecto.Repo.Schema.apply/4
    (ecto 3.11.1) lib/ecto/repo/schema.ex:377: anonymous fn/15 in Ecto.Repo.Schema.do_insert/4
    (ecto 3.11.1) lib/ecto/association.ex:1584: Ecto.Association.ManyToMany.on_repo_change/5
    (ecto 3.11.1) lib/ecto/association.ex:648: anonymous fn/8 in Ecto.Association.on_repo_change/7
    (elixir 1.15.4) lib/enum.ex:2510: Enum."-reduce/3-lists^foldl/2-0-"/3
    (ecto 3.11.1) lib/ecto/association.ex:644: Ecto.Association.on_repo_change/7
    (elixir 1.15.4) lib/enum.ex:2510: Enum."-reduce/3-lists^foldl/2-0-"/3
    (ecto 3.11.1) lib/ecto/association.ex:589: Ecto.Association.on_repo_change/4
    (ecto 3.11.1) lib/ecto/repo/schema.ex:955: Ecto.Repo.Schema.process_children/5
    (ecto 3.11.1) lib/ecto/repo/schema.ex:1033: anonymous fn/3 in Ecto.Repo.Schema.wrap_in_transaction/6
    (ecto_sql 3.11.1) lib/ecto/adapters/sql.ex:1358: anonymous fn/3 in Ecto.Adapters.SQL.checkout_or_transaction/4
    (db_connection 2.6.0) lib/db_connection.ex:1710: DBConnection.run_transaction/4
    (medussa_studio 0.1.0) lib/medussa_studio_web/live/appointment_live/form_component.ex:117: MedussaStudioWeb.AppointmentLive.FormComponent.save_appointment/3
    (phoenix_live_view 0.20.7) lib/phoenix_live_view/channel.ex:729: anonymous fn/4 in Phoenix.LiveView.Channel.inner_component_handle_event/4
    (telemetry 1.2.1) /Users/amir/Desktop/medussa_studio/deps/telemetry/src/telemetry.erl:321: :telemetry.span/3
    (phoenix_live_view 0.20.7) lib/phoenix_live_view/diff.ex:209: Phoenix.LiveView.Diff.write_component/4
    (phoenix_live_view 0.20.7) lib/phoenix_live_view/channel.ex:661: Phoenix.LiveView.Channel.component_handle/4
    (stdlib 5.0.2) gen_server.erl:1077: :gen_server.try_handle_info/3
    (stdlib 5.0.2) gen_server.erl:1165: :gen_server.handle_msg/6

Any help appreciated.
Thanks!