https://github.com/burgalon/mongoid_optimistic_locking

Addon for Mongoid to allow optimistic locking (CAS)
https://github.com/burgalon/mongoid_optimistic_locking

Last synced: about 23 hours ago
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Addon for Mongoid to allow optimistic locking (CAS)

• Host: GitHub
• URL: https://github.com/burgalon/mongoid_optimistic_locking
• Owner: burgalon
• License: mit
• Created: 2012-01-25T16:28:50.000Z (almost 13 years ago)
• Default Branch: master
• Last Pushed: 2013-04-26T18:23:31.000Z (over 11 years ago)
• Last Synced: 2024-03-15T02:47:13.789Z (8 months ago)
• Language: Ruby
• Homepage:
• Size: 133 KB
• Stars: 41
• Watchers: 5
• Forks: 14
• Open Issues: 1
• Metadata Files:
  • Readme: README.md
  • License: LICENSE

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README

        
# mongoid\_optimistic\_locking

This gem helps to abstract the ["Update if Current"](http://www.mongodb.org/display/DOCS/Atomic+Operations#AtomicOperations-%22UpdateifCurrent%22) method which may be used as a replacement for [transactions in Mongo](http://docs.mongodb.org/manual/faq/developers/#how-do-i-do-transactions-and-locking-in-mongodb).

The gem is an addon over [Mongoid ODM](http://mongoid.org/) and is based on [ActiveRecord's Optimistic Locking](http://api.rubyonrails.org/classes/ActiveRecord/Locking/Optimistic.html).

## Compatibility

Works with *Mongoid 3*.

For Mongoid 2 use version 0.0.2

## Rails 3 Installation

Add the gem to your `Gemfile`:

    gem 'mongoid_optimistic_locking'

## Usage

To use it, all you have to do is add include `Mongoid::OptimisticLocking`:

    class Post

      include Mongoid::Document

      include Mongoid::OptimisticLocking

      field :text

    end

This will add a `_lock_version` field in the document which will be incremented every time a save is called.

Be sure to rescue `Mongoid::Errors::StaleDocument` to handle applicative logic in case the object was changed.

For example:

    class PostController < ApplicationController

      ## Adds an "UPDATE: ...some text..." to an existing document

      def add_update

        begin

          post = Post.find(params[:id])

          post.text += "---UPDATE---  " + params[:more_text]

          post.save

        rescue Mongoid::Errors::StaleDocument

          retry

        end

      end

    end

That's it!

## Embedded Document Caveats

While `Mongoid::OptimisticLocking` can be used to some degree within embedded documents, there are certain limitations due to Mongoid's document embedding callback structure. Consider the following example:

    class Post

      include Mongoid::Document

      field :text

      embeds_many :comments

    end

    class Comment

      include Mongoid::Document

      include Mongoid::OptimisticLocking

      embedded_in :post

      field :text

    end

    post = Post.new

    comment = post.comments.build(:text => 'hello')

    comment.save # will use optimistic locking checks

    post.save # will not use optimistic locking checks

## Open sourced by

[Boxee](http://www.boxee.tv)

## References

[Mongo Developer FAQ - How do I do transactions/locking?](http://docs.mongodb.org/manual/faq/developers/#how-do-i-do-transactions-and-locking-in-mongodb)

[Mongo Atomic Operations - "Update if Current"](http://www.mongodb.org/display/DOCS/Atomic+Operations#AtomicOperations-%22UpdateifCurrent%22)

[Presentation from "Startup Day" on Mongoid Optimistic Locking](https://speakerdeck.com/u/burgalon/p/mongoid-optimistic-locking)