Valkyrie

Valkyrie is a gem for enabling multiple backends for storage of files and metadata in Samvera.

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Primary Contacts

Product Owner

Carolyn Cole

Technical Lead

Trey Pendragon

Installation

Add this line to your application's Gemfile:

gem 'valkyrie'

And then execute:

$ bundle

Configuration

Valkyrie is configured in two places: an initializer that registers the persistence options and a YAML configuration file that sets which options are used by default in which environments.

Sample initializer: config/initializers/valkyrie.rb:

Here is a sample initializer that registers a couple adapters and storage adapters, in each case linking an instance with a short name that can be used to refer to it in your application:

# frozen_string_literal: true
require 'valkyrie'
Rails.application.config.to_prepare do
  Valkyrie::MetadataAdapter.register(
    Valkyrie::Persistence::Postgres::MetadataAdapter.new,
    :postgres
  )

  Valkyrie::MetadataAdapter.register(
    Valkyrie::Persistence::Memory::MetadataAdapter.new,
    :memory
  )

  Valkyrie::StorageAdapter.register(
    Valkyrie::Storage::Disk.new(base_path: Rails.root.join("tmp", "files")),
    :disk
  )

  Valkyrie::StorageAdapter.register(
    Valkyrie::Storage::Fedora.new(connection: Ldp::Client.new("http://localhost:8988/rest")),
    :fedora
  )


  Valkyrie::StorageAdapter.register(
    Valkyrie::Storage::Memory.new,
    :memory
  )
end

The initializer registers two Valkyrie::MetadataAdapter instances for storing metadata:

  • :postgres which stores metadata in a PostgreSQL database
  • :memory which stores metadata in an in-memory cache (this cache is not persistent, so it is only appropriate for testing)

Other adapter options include Valkyrie::Persistence::BufferedPersister for buffering in memory before bulk updating another persister, Valkyrie::Persistence::CompositePersister for storing in more than one adapter at once, Valkyrie::Persistence::Solr for storing in Solr, and Valkyrie::Persistence::Fedora for storing in Fedora.

The initializer also registers three Valkyrie::StorageAdapter instances for storing files:

  • :disk which stores files on disk
  • :fedora which stores files in Fedora
  • :memory which stores files in an in-memory cache (again, not persistent, so this is only appropriate for testing)

Sample configuration: config/valkyrie.yml:

A sample configuration file that configures your application to use different adapters:

development:
  metadata_adapter: postgres
  storage_adapter: disk

test:
  metadata_adapter: memory
  storage_adapter: memory

production:
  metadata_adapter: postgres
  storage_adapter: fedora

For each environment, you must set two values:

  • metadata_adapter is the store where Valkyrie will put the metadata
  • storage_adapter is the store where Valkyrie will put the files

The values are the short names used in your initializer.

Further details can be found on the the Wiki.

Usage

The Public API

Valkyrie's public API is defined by the shared specs that are used to test each of its core classes. This include change sets, resources, persisters, adapters, and queries. When creating your own kinds of these kinds of classes, you should use these shared specs to test your classes for conformance to Valkyrie's API.

When breaking changes are introduced, necessitating a major version change, the shared specs will reflect this. When new features are added and a minor version is released there will be no change to the existing shared specs, but there may be new ones. These new shared specs will fail in your application if you have custom adapters, but your application will still work.

Using the shared specs in your own models is described in more detail.

Define a Custom Work

Define a custom work class:

# frozen_string_literal: true
class MyModel < Valkyrie::Resource
  include Valkyrie::Resource::AccessControls
  attribute :title, Valkyrie::Types::Set    # Sets deduplicate values
  attribute :date, Valkyrie::Types::Array   # Arrays can contain duplicate values
end

Attributes are unordered by default. Adding ordered: true to an attribute definition will preserve the order of multiple values.

attribute :authors, Valkyrie::Types::Array.meta(ordered: true)

Defining resource attributes is explained in greater detail within the Wiki.

Work Types Generator

To create a custom Valkyrie model in your application, you can use the Rails generator. For example, to generate a model named FooBar with an unordered title field and an ordered member_ids field:

rails generate valkyrie:resource FooBar title member_ids:array

You can namespace your model class by including a slash in the model name:

rails generate valkyrie:resource Foo/Bar title member_ids:array

Read and Write Data

# initialize a metadata adapter
adapter = Valkyrie::MetadataAdapter.find(:postgres)

# create an object
object1 = MyModel.new title: 'My Cool Object', authors: ['Jones, Alice', 'Smith, Bob']
object1 = adapter.persister.save(resource: object1)

# load an object from the database
object2 = adapter.query_service.find_by(id: object1.id)

# load all objects
objects = adapter.query_service.find_all

# load all MyModel objects
Valkyrie.config.metadata_adapter.query_service.find_all_of_model(model: MyModel)

The usage of ChangeSets in writing data are further documented here.

Concurrency Support (Optimistic Locking)

By default, it is assumed that a Valkyrie repository implementation shall use a solution supporting concurrent updates for resources (multiple resources can be updated simultaneously using a Gem such as Sidekiq). In order to handle the possibility of multiple updates applied to the same resource corrupting data, Valkyrie supports optimistic locking. For further details, please reference the overview of optimistic locking for Valkyrie resources.

Installing a Development environment

Without Docker

External Requirements

  • PostgreSQL with the uuid-ossp extension.
    • Note: Enabling uuid-ossp requires database superuser privileges.
    • From psql: alter user [username] with superuser;

To run the test suite

  1. Start Solr and Fedora servers for testing with rake server:test
  2. Run rake db:create (First time only)
  3. Run rake db:migrate

With Docker

External Requirements

  • Docker version >= 17.09.0 * ### Dependency Setup (Mac OSX)
  1. brew install docker
  2. brew install docker-machine
  3. brew install docker-compose

Starting Docker (Mac OSX)

  1. docker-machine create default
  2. docker-machine start default
  3. eval "$(docker-machine env)"

Starting the development mode dependencies

  1. Start Solr, Fedora, and PostgreSQL with rake docker:dev:daemon (or rake docker:dev:up in a separate shell to run them in the foreground)
  2. Run rake db:create db:migrate to initialize the database
  3. Develop!
  4. Run rake docker:dev:down to stop the server stack
    • Development servers maintain data between runs. To clean them out, run rake docker:dev:clean

To run the test suite with all dependencies in one go

  1. rake docker:spec

To run the test suite manually

  1. Start Solr, Fedora, and PostgreSQL with rake docker:test:daemon (or rake docker:test:up in a separate shell to run them in the foreground)
  2. Run rake db:create db:migrate to initialize the database
  3. Run the gem's RSpec test suite with rspec spec or rake
  4. Run rake docker:test:down to stop the server stack
    • The test stack cleans up after itself on exit.

The development and test stacks use fully contained virtual volumes and bind all services to different ports, so they can be running at the same time without issue.

Get Help

If you have any questions regarding Valkyrie you can send a message to the Samvera community tech list or the #valkyrie channel in the Samvera community Slack team.

License

Valkyrie is available under the Apache 2.0 license.

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/samvera-labs/valkyrie/.