KamilLelonek

defmodule PostgresPubSub.Repo.Migrations.CreateAccounts do
  use Ecto.Migration

  def change do
    create_if_not_exists table(:accounts) do
      add(:username, :string, null: true)
    end
  end
end

KamilLelonek

defmodule PostgresPubSub.Listener do
  # ...

  require Logger

  @impl true
  def handle_info({:notification, _pid, _ref, "accounts_changed", payload}, _state) do
    with {:ok, data} <- Poison.decode(payload, keys: :atoms) do
      data
      |> inspect()

KamilLelonek

defmodule PostgresPubSub.Listener do
  use GenServer

  def child_spec(opts) do
    %{
      id: __MODULE__,
      start: {__MODULE__, :start_link, [opts]}
    }
  end

KamilLelonek

defmodule PostgresPubSub.Repo do
  # ...

  def listen(event_name) do
    with {:ok, pid} <- Postgrex.Notifications.start_link(__MODULE__.config()),
         {:ok, ref} <- Postgrex.Notifications.listen(pid, event_name) do
      {:ok, pid, ref}
    end
  end
end

KamilLelonek

defmodule PostgresPubSub.Application do
  use Application

  def start(_type, _args),
    do: Supervisor.start_link(children(), opts())

  defp children do
    [
      PostgresPubSub.Repo
    ]

KamilLelonek

defmodule PostgresPubSub.Repo do
  use Ecto.Repo,
    otp_app: :postgres_pubub

  def child_spec(opts) do
    %{
      id: __MODULE__,
      start: {__MODULE__, :start_link, [opts]},
      type: :supervisor
    }

KamilLelonek

CREATE TRIGGER accounts_changed
AFTER INSERT OR UPDATE
ON accounts
FOR EACH ROW
EXECUTE PROCEDURE notify_account_changes()

KamilLelonek

CREATE OR REPLACE FUNCTION notify_account_changes()
RETURNS trigger AS $$
BEGIN
  PERFORM pg_notify(
    'accounts_changed',
    json_build_object(
      'operation', TG_OP,
      'record', row_to_json(NEW)
    )::text
  );

KamilLelonek

defmodule MinimalServer.Application do
  # ...

  defp children do
    [
      MinimalServer.Endpoint
    ]
  end
end

KamilLelonek

 defmodule MinimalServer.Endpoint do
   # ...
   
   def child_spec(opts) do
    %{
      id: __MODULE__,
      start: {__MODULE__, :start_link, [opts]}
    }
  end