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.

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).
• 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.

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.