Boltun simplifies handling of the LISTEN/NOTIFY mechanism offered by Postgres. Basically you will just need to define which callback(s) should be called on a specific notification and that's it

Add Boltun as a dependency in your mix.exs file.

defp deps do
  [{:boltun, "~> 1.0.2"}]
end

After you are done, run mix deps.get in your shell to fetch the dependencies.

Defining a listener is trivial. See the example below

defmodule TestListener do
  use Boltun, otp_app: :my_app

  listen do
    channel "my_channel", :my_callback
    channel "my_channel", :my_other_callback
    channel "my_other_channel", :my_other_callback
  end

  def my_callback(channel, payload) do
    IO.puts channel
    IO.puts payload
  end
  ...
end

The channel is a concept defined by Postgres. On the SQL side you will have something like NOTIFY my_channel, 'my payload' happening, for example, in a trigger which will cause your callbacks TestListener.my_callback and TestListener.my_other_callback to be called. The callbacks will be invoked synchronously in the order they were declared in the listen block.

Defining a listener is not enough to use it. It should be started with TestListener.start_link. You can do this, for example, in a supervisor. The listener also needs the connection parameters to establish a connection. You will provide this in your config.exs file in this format

  ...
  config :my_app, TestListener, database: "postgres", username: "postgres", password: "postgres", hostname: "localhost"
  ...

The full list of options can be read in the documentation for Postgrex.

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