Module: OAI::Provider

Included in:

Base

Defined in:

lib/oai/provider.rb,
lib/oai/provider/model.rb,
lib/oai/provider/response.rb,
lib/oai/provider/partial_result.rb,
lib/oai/provider/resumption_token.rb,
lib/oai/provider/model/activerecord_wrapper.rb,
lib/oai/provider/model/activerecord_caching_wrapper.rb

Overview

OAI::Provider

Open Archives Initiative - Protocol for Metadata Harvesting see www.openarchives.org/

Features

• Easily setup a simple repository

• Simple integration with ActiveRecord

• Dublin Core metadata format included

• Easily add addition metadata formats

• Adaptable to any data source

• Simple resumption token support

Usage

To create a functional provider either subclass Provider::Base, or reconfigure the defaults.

Sub classing a provider

class MyProvider < Oai::Provider
  repository_name 'My little OAI provider'
  repository_url  'http://localhost/provider'
  record_prefix 'oai:localhost'
  admin_email 'root@localhost'   # String or Array
  source_model MyModel.new       # Subclass of OAI::Provider::Model
end

Configuring the default provider

class Oai::Provider::Base
  repository_name 'My little OAI Provider'
  repository_url 'http://localhost/provider'
  record_prefix 'oai:localhost'
  admin_email 'root@localhost'
  source_model MyModel.new
end

The provider does allow a URL to be passed in at request processing time in case the repository URL cannot be determined ahead of time.

Integrating with frameworks

Camping

In the Models module of your camping application post model definition:

class CampingProvider < OAI::Provider::Base
  repository_name 'Camping Test OAI Repository'
  source_model ActiveRecordWrapper.new(YOUR_ACTIVE_RECORD_MODEL)
end

In the Controllers module:

class Oai
  def get
    @headers['Content-Type'] = 'text/xml'
    provider = Models::CampingProvider.new
    provider.process_request(@input.merge(:url => "http:"+URL(Oai).to_s))
  end
end

The provider will be available at “/oai”

Rails

At the bottom of environment.rb create a OAI Provider:

# forgive the standard blog example.

require 'oai'
class BlogProvider < OAI::Provider::Base
  repository_name 'My little OAI Provider'
  repository_url 'http://localhost:3000/provider'
  record_prefix 'oai:blog'
  admin_email 'root@localhost'
  source_model OAI::Provider::ActiveRecordWrapper.new(Post)
end

Create a custom controller:

class OaiController < ApplicationController
  def index
    # Remove controller and action from the options.  Rails adds them automatically.
    options = params.delete_if { |k,v| %w{controller action}.include?(k) }
    provider = BlogProvider.new
    response =  provider.process_request(options)
    render :text => response, :content_type => 'text/xml'
  end
end

Special thanks to Jose Hales-Garcia for this solution.

Supporting custom metadata formats

See Oai::Metadata for details.

ActiveRecord Integration

ActiveRecord integration is provided by the ActiveRecordWrapper class. It takes one required paramater, the class name of the AR class to wrap, and optional hash of options.

Valid options include:

• timestamp_field - Specifies the model field to use as the update filter. Defaults to ‘updated_at’.

• limit - Maximum number of records to return in each page/set. Defaults to 100. The wrapper will paginate the result via resumption tokens.

  Caution: specifying too large a limit will adversely affect performance.

Mapping from a ActiveRecord object to a specific metadata format follows this set of rules:

1. Does Model#to_metadata_prefix exist? If so just return the result.

2. Does the model provide a map via Model.map_metadata_prefix? If so use the map to generate the xml document.

3. Loop thru the fields of the metadata format and check to see if the model responds to either the plural, or singular of the field.

For maximum control of the xml metadata generated, it’s usually best to provide a ‘to_metadata_prefix’ in the model. If using Builder be sure not to include any instruct! in the xml object.

Explicit creation example

class Post < ActiveRecord::Base
  def to_oai_dc
    xml = Builder::XmlMarkup.new
    xml.tag!("oai_dc:dc", 
      'xmlns:oai_dc' => "http://www.openarchives.org/OAI/2.0/oai_dc/",
      'xmlns:dc' => "http://purl.org/dc/elements/1.1/",
      'xmlns:xsi' => "http://www.w3.org/2001/XMLSchema-instance",
      'xsi:schemaLocation' => 
        %{http://www.openarchives.org/OAI/2.0/oai_dc/ 
          http://www.openarchives.org/OAI/2.0/oai_dc.xsd}) do
        xml.tag!('oai_dc:title', title)
        xml.tag!('oai_dc:description', text)
        xml.tag!('oai_dc:creator', user)
        tags.each do |tag|
          xml.tag!('oai_dc:subject', tag)
        end
    end
    xml.target!
  end
end

Mapping Example

# Extremely contrived mapping
class Post < ActiveRecord::Base
  def self.map_oai_dc
    {:subject => :tags, 
     :description => :text, 
     :creator => :user, 
     :contibutor => :comments}
  end
end

Defined Under Namespace

Modules: Metadata, Response Classes: ActiveRecordCachingWrapper, ActiveRecordWrapper, Base, Model, OaiEntry, OaiToken, PartialResult, ResumptionToken