Touring the design patterns in Samvera

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cc-by-nd: 8barbikes

Where are we? What are we doing here?

• Working code wins
• Go far together
• Scratch your own itch
• "The Rails Way"
• The Model-View-Controller (MVC) Pattern

Where are we going?
What are our goals?
Where to next?

Maintainable software

Well defined interfaces

Fewer included modules

Customize without contortions to override controller/helper methods

Keep it working

SOLID: The first five principles

• Single responsibility
• Open for extension, closed for modification
• Liskov substitution
• Interface Segregation
• Dependency Inversion

Anti-pattern: Rails Helpers

cc-by-nc: Edmund White

Solution: Presenter

cc-by-nc: Steve McFarland

a.k.a.: Decorator or View-Model

Presenter

class BookPresenter
  def initialize(book)
    @book = book
  end

  delegate :title, :creator, to: :@book

  def glitter_title
    '★' + @book.title + '☆'
  end
end

Presenter usage

class BooksController < ApplicationController
  def show
    book = Book.find(params[:id])
    @presenter = BookPresenter.new(book)
  end
end

In real code

Hands on exercise

cc-by: Timmy_L

• Start up the VM
• Log into Hyrax

Task: Display a new field 'restrictions'

Start up the VM

$ vagrant up
$ vagrant ssh

Change directory to the Hyrax sample application

$ cd hyrax-sample

Generate Hyrax application

If you're using the provided VM, this is already done. You can skip this step.

If you don't already have Rails 5+ installed

$ gem install rails -v 5.0.0.1

$ rails new hyrax-sample -m
                https://raw.githubusercontent.com/samvera/hyrax/master/template.rb

Generate a book

$ rails generate hyrax:work Book

Start up the services

Open 3 more terminal windows. In each window:

$ vagrant ssh
$ cd hyrax-sample

Start up the services

Start Solr: $ solr_wrapper

Start Fedora: $ fcrepo_wrapper

Start Rails: $ rails server -b 0.0.0.0

Create an account

When you see Listening on tcp://0.0.0.0:3000 the server is ready to visit at http://localhost:3000/

* If you're using Rails 4, you'll see WEBrick::HTTPServer#start: pid=5962 port=3000 instead.

Create a presenter

Task: Display a new field 'restrictions'

in the fourth terminal window:

$ mkdir app/presenters
$ nano app/presenters/book_presenter.rb

Create a presenter

# app/presenters/book_presenter.rb
class BookPresenter < Hyrax::WorkShowPresenter
  delegate :restrictions, to: :solr_document
end

* You need to restart your rails server

Update the solr document

# app/models/solr_document.rb
class SolrDocument
  ...
  def restrictions
    fetch('restrictions_tesim', ['nothing'])
  end
  ...
end

Update the controller

# app/controllers/hyrax/books_controller.rb
module Hyrax
  class BooksController < ApplicationController
    include Hyrax::WorksControllerBehavior
    include Hyrax::BreadcrumbsForWorks
    self.curation_concern_type = Book

    # Set our custom presenter
    self.show_presenter = ::BookPresenter
  end
end

Update the view partial

$ cp `bundle show hyrax`/app/views/hyrax/base/_attribute_rows.html.erb
      app/views/hyrax/books/

$ nano app/views/hyrax/books/_attribute_rows.html.erb
      

Update the view partial

# app/view/hyrax/books/_attribute_rows.html.erb
<%= presenter.attribute_to_html(:description) %>
<%= presenter.attribute_to_html(:creator, render_as: :linked ) %>
...
<%= presenter.attribute_to_html(:source) %>

<%= presenter.attribute_to_html(:restrictions) %>
      

View your work

Update the a presenter

# app/presenters/book_presenter.rb
class BookPresenter < Hyrax::WorkShowPresenter
  # delegate :restrictions, to: :solr_document

  def restrictions
    if solr_document.restrictions.first == 'nothing'
     "There are no restrictions on this object"
    else
      solr_document.restrictions
    end
  end
end

Presenters in conclusion

• A pattern to encapsulate helpers that work on a particular model
• Also called decorators or view-models
• You can find them in hydra-editor and hyrax
• In Samvera the Presenter is delegating to a SolrDocument

Forms

Like a presenter but backed by a ActiveFedora object, not a SolrDocument

Task: Add 'restrictions' to the create/edit page.

Customize the model

# app/models/book.rb
class Book < ActiveFedora::Base
  include ::Hyrax::WorkBehavior
  include ::Hyrax::BasicMetadata
  # Change this to restrict which works can be added as a child.
  # self.valid_child_concerns = []
  validates :title, presence: { message: 'Your work must have a title.' }
  property :restrictions, predicate: ::RDF::Vocab::DC.accessRights do |index|
    index.as :stored_searchable
  end
  self.human_readable_type = 'Book'
end

Customize the form

# app/forms/hyrax/book_form.rb
module Hyrax
  class BookForm < Hyrax::Forms::WorkForm
    self.model_class = ::Book

    self.terms += [:resource_type, :restrictions]
  end
end

Maybe make the property single value?

# app/models/book.rb
  ...
  property :restrictions, predicate: ::RDF::Vocab::DC.accessRights, multiple: false do |index|
    index.as :stored_searchable
  end
  ...

Forms in conclusion

• Just like a presenter, but with an ActiveFedora object instead of a SolrDocument
• Follows the decorator/view-model pattern
• You can find them in hydra-editor and hyrax

Anti-pattern: bloated services

cc-by-nc-nd: Rob Lucas

Solution: Stack

cc-by: Mark B. Schlemmer

Actor Stack

Actor Stack: In the wild

# app/actors/hyrax/actors/add_as_member_of_collections_actor.rb
class AddAsMemberOfCollectionsActor < AbstractActor
  def create(attributes)
    collection_ids = attributes.delete(:member_of_collection_ids)
    add_to_collections(collection_ids) && next_actor.create(attributes)
  end

  def update(attributes)
    collection_ids = attributes.delete(:member_of_collection_ids)
    add_to_collections(collection_ids) && next_actor.update(attributes)
  end
  private
  ...
end

Create actor

# app/actors/hyrax/actors/metadata_enrichment_actor.rb
module Hyrax
  module Actors
    class MetadataEnrichmentActor < Hyrax:Actors:BaseActor
      def create(attributes)
        enrich_metadata(attributes) && next_actor.create(attributes)
      end

      private
        def enrich_metadata(attributes)
          if attributes.fetch('creator').include?("Carla Hayden")
            attributes['description'] << "She's the Librarian of Congress"
          end
          true
        end
    end
  end
end

Add actor to the stack

$ mkdir -p app/services/hyrax
  $ cp `bundle show hyrax`/app/services/hyrax/actor_factory.rb app/services/hyrax/
  

# app/services/hyrax/actor_factory.rb
module Hyrax
  class ActorFactory
    def self.stack_actors(curation_concern)
      [MetadataEnrichmentActor,
        CreateWithRemoteFilesActor,
        CreateWithFilesActor,
        Hyrax::Actors::AddAsMemberOfCollectionsActor,
        Hyrax::Actors::AddToWorkActor,
        Hyrax::Actors::AssignRepresentativeActor,
        Hyrax::Actors::AttachFilesActor,
         ....
       model_actor(curation_concern),
       # Initialize workflow after model is saved
       Hyrax::Actors::InitializeWorkflowActor]
    end
  end
end

Add actor to the stack

Since we just changed an initializer, we'll need to restart the Rails server. Now try it out!

Actor stack in conclusion

• An ordered collection of classes that implement create and update
• The create/update methods return true to continue and false to abort
• Inspired by Rack middleware
• Still needs work to be more configurable by end users

Anti-pattern: bloated controller

cc-by-nc: Brad Hammonds

Search Builders

• Build a query for the index (Solr)
• Decouples the controller from the index implementation
• Allows us to build queries outside of the Controller
• Blacklight generates one for you: app/models/search_builder.rb

Search Builder: In the wild

# hyrax: app/search_builders/hyrax/catalog_search_builder.rb
class Hyrax::CatalogSearchBuilder < ::SearchBuilder
  self.default_processor_chain += [
    :add_access_controls_to_solr_params,
    :show_works_or_works_that_contain_files,
    :show_only_active_records
  ]
  ...
end

Search Builder: In the wild (cont.)

# hyrax: app/search_builders/hyrax/catalog_search_builder.rb
class Hyrax::CatalogSearchBuilder < ::SearchBuilder
  ...
  # show both works that match the query and works that contain files that match the query
    def show_works_or_works_that_contain_files(solr_parameters)
        return if blacklight_params[:q].blank? || blacklight_params[:search_field]
        solr_parameters[:user_query] = blacklight_params[:q]
        solr_parameters[:q] = new_query
    end

    # show works that are in the active state.
    def show_only_active_records(solr_parameters)
      solr_parameters[:fq] ||= []
      solr_parameters[:fq] << '-suppressed_bsi:true'
    end
    ...
end

Search Builder: In the wild (cont.)

# hyrax: app/search_builders/hyrax/filter_by_type.rb
module FilterByType
  ...
  # Add queries that excludes everything except for works and collections
  def filter_models(solr_parameters)
    solr_parameters[:fq] ||= []
    solr_parameters[:fq] << "{!terms f=has_model_ssim}#{models_to_solr_clause}"
  end
  ...
  protected
  ...
    # Override this method if you want to filter for a different set of models.
      # @return [Array] a list of classes to include
    def models
      work_classes + collection_classes
    end
  private
  ...
    def models_to_solr_clause
      # to_class_uri is deprecated in AF 11
      [ActiveFedora::Base.respond_to?(:to_rdf_representation) ? models.map(&:to_rdf_representation) : models.map(&:to_class_uri)].join(',')
    end
  ...
end

Exercise

Create a search builder that finds books by a particular person

# app/models/created_by_search_builder.rb
class CreatedBySearchBuilder < Blacklight::SearchBuilder
  include Blacklight::Solr::SearchBuilderBehavior
  include Hydra::AccessControlsEnforcement
  include Hyrax::SearchFilters

  self.default_processor_chain = [:for_users]
  def for_users(solr_parameters)
    solr_parameters[:fq] ||= []
    solr_parameters[:fq] << "{!field f=creator_tesim v=#{blacklight_params[:q][:creator]}}"
  end
end

Exercise

builder = CreatedBySearchBuilder.new(nil).with(creator: 'Carla
  Hayden')
builder.query
  => {"facet.field"=>[], "facet.query"=>[], "facet.pivot"=>[],
      "fq"=>["{!field f=creator_tesim v=Carla Hayden}"], "hl.fl"=>[]}

Exercise

Create a search builder that finds books by a particular person

repository = CatalogController.new.repository
builder = CreatedBySearchBuilder.new(nil).where(creator: 'Carla Hayden')
response = repository.search(builder)
response.documents

Fin

cc-by-sa: Brandon O'Connor