activerecord-postgres_pub_sub

This gem contains support for PostgreSQL LISTEN and NOTIFY functionality: doc.

Installation

Add this line to your application's Gemfile:

gem "activerecord-postgres_pub_sub"

And then execute:

$ bundle

Or install it yourself as:

$ gem install activerecord-postgres_pub_sub

Usage

Listener

The Listener class is used to handle notification messages on one or more channels.

The listener can be configured with three blocks:

• on_notify: called whenever a notification is received.
• on_start: called before receiving any notifications.
• on_timeout: called based on a configurable timeout, when no notifications have been received.

When creating a listener, the following configuration is supported:

• listen_timeout: If set, the on_timeout block will be called if no notifications are received within this period. (Default nil).
• notify_only: A payload string can be included in notifications. By default the listener ignores the payload and coalesces multiple notifications into a single call. When this option is false, the on_notify block is called with the payload for each notification. (Default true).
• base_class: An Active Record class should you need to use a different base class (e.g. for multiple database support). (Default ActiveRecord::Base).
• exclusive_lock: Acquire a lock using with_advisory_lock prior to listening. This option ensures that a process as a singleton listener. (Default true).

Example:

ActiveRecord::PostgresPubSub::Listener.listen("notify_channel", listen_timeout: 30) do |listener|
  listener.on_start do
    # when starting assume we missed something and perform regular activity
    handle_notification
  end

  listener.on_notify do
    handle_notification
  end

  listener.on_timeout do
    perform_regular_maintenance
  end
end

Generator

This gem contains a Rails generator for a migration to add a trigger to notify on insert to a table.

The generator must be run with a model name corresponding to the table.

rails generate active_record:postgres_pub_sub:notify_on_insert --model_name NameSpace::Entity

In this example, notification events would be generated for the channel named "name_space_entity" based on inserts to the name_space_entities table.

Supported dependencies

This gem will not support versions of ruby and activerecord which no longer receive security updates. It will support the latest major version of the pg gem and it will be tested against the latest minor / patch version of that gem.

Development

After checking out the repo, run bin/setup to install dependencies. Then, run rake spec to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install.

To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to rubygems.org.

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/ezcater/activerecord-postgres_pub_sub.

License

The gem is available as open source under the terms of the MIT License.