ruby-oai is a Open Archives Protocol for Metadata Harvesting (OAI-PMH) library for Ruby. OAI-PMH is a somewhat archaic protocol for sharing metadata between digital library repositories. If you are looking to share metadata on the web you are probably better off using a feed format like RSS or Atom. If have to work with a backwards digital repository that only offers OAI-PMH access then ruby-oai is your friend.
The OAI-PMH spec defines six verbs
(Identify, ListIdentifiers, ListRecords,
GetRecords, ListSets, ListMetadataFormat) used for discovery and sharing of
metadata.
The ruby-oai gem includes a client library, a server/provider library and a interactive harvesting shell.
The OAI client library is used for harvesting metadata from repositories. For example to initiate a ListRecords request to pubmed you can:
require 'oai'
client = OAI::Client.new 'http://www.pubmedcentral.gov/oai/oai.cgi', :headers => { "From" => "[email protected]" }
response = client.list_records
# Get the first page of records
response.each do |record|
puts record.metadata
end
# Get the second page of records
response = client.list_records(:resumption_token => response.resumption_token)
response.each do |record|
puts record.metadata
end
# Get all pages together (may take a *very* long time to complete)
client.list_records.full.each do |record|
puts record.metadata
endThis library depends on faraday, but allows a wide range of versions. Depending on the client application's installed version of faraday, there may be different middleware libraries required to support automatically retrying requests that are rate limited/denied with a Retry-After header. The OAI client can, however, accept an externally configured faraday http client for handling this. For example, to retry on 429 Too Many Requests:
require 'oai'
require 'faraday_middleware' # if using faraday version < 2
http_client = Faraday.new do |conn|
conn.request(:retry, max: 5, retry_statuses: 429)
conn.response(:follow_redirects, limit: 5)
conn.adapter :net_http
end
client = OAI::Client.new(base_url, http: http_client)
opts = {from:'2012-03-01', until:'2012-04-01', metadata_prefix:'oai_dc'}
puts client.list_records(opts).full.countSee {OAI::Client} for more details
The OAI provider library handles serving local content to other clients. Here's how to set up a simple 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
endSee comment docs at top of OAI::Provider for more details, including discussion of the OAI::Provider::ActiveRecordWrapper class for quich setup of an OAI provider for an ActiveRecord model class (single database table)
The OAI-PMH client shell allows OAI Harvesting to be configured in an interactive manner. Typing oai on the command line starts the shell. After initial configuration, the shell can be used to manage harvesting operations.
See {OAI::Harvester::Shell} for more details
Normally the best way to install oai is as part of your Gemfile:
source :rubygems
gem 'oai'
Alternately it can be installed globally using RubyGems:
$ gem install oai
Tests are with Test::Unit, in a somewhat archaic/legacy style. Test setup especially is not how we would do things today. Run all tests with:
$ bundle exec rake test
There are also convenience tasks to run subsets of tests.
We use appraisal to test ActiveRecord-related functionality under multiple versions of ActiveRecord. While the above commands will test with latest ActiveRecord (allowed in our .gemspec development dependency), you can test under a particular version defined in the Appraisals file like so:
$ bundle exec appraisal rails-52 rake test
$ bundle exec appraisal rails-70 rake test
If you run into trouble with appraisal's gemfiles getting out of date and bundler complaining, try:
$ bundle exec appraisal clean $ appraisal generate
That may make changes to appraisal gemfiles that you should commit to repo.