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Automatically store a version of a MongoMapper document every time it's updated. Configure a maximum number of versions you'd like to keep, or even the amount of time a particular document should keep versions around.

Add the gem to your Gemfile. Add the necessary Mongo indexes: run Version.create_indexes in your console, or if you are using Rails run the rake versioned:create_indexes command.

Add the versioned declaration to the MongoMapper document models you want to keep versions of. When you update a versioned document, a new version will be stored. Deleting a stored document will delete all the associated versions.

class User
  versioned

  key :name, String
  key :email, String
end

Every versioned document model has an association called versions that contains all past versions of a document. It's a plain old MongoMapper one-to-many association with the Version model, sorted in reverse chronological order. You can query for versions using MongoMapper's standard query criteria:

@user.versions.where(:created_at.lt > 1.day.ago)

Use the max option to specifiy the maximum number of versions you want to keep. When the document is updated, the oldest versions will be pruned away to keep no more than the maximum number you specify.

class User
  versioned max: 10

  key :name, String
  key :email, String
end

If you'd rather specify the amount of time the versions of a doc should be kept, implement keep_versions_for. It must return the number of seconds to keep each revision. Every time a new version is created, versions will be purged based on their age.

This doesn't work with the max option. Use one or the other.

class User
  versioned

  key :name, String
  key :email, String

  def keep_versions_for
    90.days
  end
end

Attempting to update a document with an old version_id will result in a Versioned::ConflictingVersionError. Use the error's version_id accessor to get the version of the currently stored document.

This feature is meant to prevent you from over-writing someone else's changes and give you the option of resolving the conflict gracefully:

@user = User.first
@user.name = "Bobby"
begin
  @user.save
rescue Versioned::ConflictingVersionError => e
  # Keep your changes
  @user.version_id = e.version_id
  @user.save

  # Or keep other person's changes
  # @user.reload
end

When a versioned document is saved, you can pass the updater option to the save method. The associated version will keep a reference to the document passed. This allows you to keep track of who made a change to a versioned document.

@reginold = User.find_by_email('reggie@hotmail.com')
@user.name = "Bob"
@user.save(:updater => @reginold)
@user.versions.first.updater
=> @reginold

Each Version contains a copy of the document as it existed at a point in time. You can roll back to a particular version by calling the rollback method on the document, passing the version.

@user.versions.count
=> 9
version = @user.versions[5]
@user.rollback(version)
=> true
@user.versions.count
=> 10
@user.version_id == @user.versions[5].version_id
=> true

Rolling back a document will create a new version representing its persisted state just prior to rollback. When you rollback a document, then make changes on top of the rolled back document, the versions collection contains two Version instances with the same version_id.

The versions collection contains all the previous versions of a document. The document itself represents the "current version." The document has a version_id key and when the document is updated its version id is stored with the Version. Then the document gets a new version_id.

Rolling back to a previous revision will also roll back the version_id value of the document.

This mechanism allows you to easily undo changes to a document:

version_id = @user.version_id
@user.name
=> "Roger"

# change some stuff
@user.name = "Frank"
@user.save
@user.name = "Bob"
@user.save

# rollback
version = @user.versions.find(version_id)
@user.rollback(version)

# document is restored
@user.name
=> "Roger"
@user.version_id == version_id
=> true