elasticsearch-rails-dynamic-json-support

Introduction

ElasticsearchRails DynamicJsonSupport - Small little change to help your model update easier in elasticsearch.

Problem it solved

In ElasicSearch, if you define your model the following way:

# app/models/article.rb
class Article < ActiveRecord::Base
  include Elasticsearch::Model
  include Elasticsearch::Model::Callbacks

  has_many :reviews

  def as_indexed_json options={}
    {
        id: id,
        title: title,
        article: content,
        created_at: created_at,
        updated_at: updated_at,
        reviews: reviews.map(&:as_json),
    }
  end

# app/models/review.rb
class Review < ActiveRecord::Base
  belongs_to :article
end

There're 2 issues with the implementation above:

• when the content is updated, this change would never be synced to the the article field in ElasticSearch, since the key is artile instead
• when the corresponding review is updated, the article is never updated, since it's not awared of the change.

This library aims to solve these 2 issues, with the following convention:

• es_json_changes(changed_attributes) - for a given set of changed attributes, it would response with the update to be processed by this record
• Elasticsearch::Model::CascadeUpdate - class, when included, providing:
  • class methods:
    • es_register_attributes { key => lambda }: to register a hash of key, lambda pairs, to be used for rendering the json. if lambda is nil, default to the public method of this resource named key.
    • key_name, relationship_name: nil, reverse_relationship_name: nil, &blk: to register an association of key, lambda. relationship_name default to key if not given, and reverse_relationship_name default to the singular form of the class name if not given. After this registration, whenever the corresponding resource is updated, it would trigger this resource (which is related to the resource) to update.

Example usage (which solves the 2 issues above) is as given below:

# app/models/article.rb
class Article < ActiveRecord::Base
  include Elasticsearch::Model
  include Elasticsearch::Model::Callbacks
  include Elasticsearch::Model::CascadeUpdate

  has_many :reviews
  es_register_attributes :id, :title, article: lambda {|rec| rec.content }

  # silent attribute would not be output by default
  es_register_silent_attributes :created_at, :updated_at 

  # register association, with: 
  #   - key_name = :reviews
  #   - get_assoc: default to be `#reviews` (the key_name)
  #   - &blk: the render_assoc, default to be: `object#as_indexed_json`. 
  #         it would use a `map` by default for the has_many relationships
  #   - reverse_class: default to guess from the relationship
  #   - reverse_trigger: lambda {|obj, changes| do_things }
  #         the reverse_trigger, when the model change, to render the json
  #         document and update the objects. the returns is an array of the
  #         original object to be updated
  es_register_assoc(:reviews) { |review| review.as_indexed_json }

  # for the given changed_attributes, it would return the json to be fed
  # into the `#update_document` method. What's given here is the default
  # behaviour -- which is to find the keys, and do a matching
  def elasticsearch_json_changes(changed_attributes)
    keys_to_update = changed_attributes.keys.map {|k| key_map k}
    self.as_indexed_json.select { |k,_| keys_to_update.include? k.to_s }
  end

  private
  def key_map(key)
    key = key.to_s
    case key
    when 'content'
      'article'
    else
      key
    end
  end
end

# app/models/review.rb
class Review < ActiveRecord::Base
  # Make sure to register Article
  Article

  belongs_to :article

  def as_indexed_json(options = {})
    as_json
  end
end

More features

• Exclusion of keys: simply call record.as_indexed_json: exclude_keys: %w[keys you do not like].
• Selective Import: es_to_json_when(scope_name, &condition_check_block). if the scope_name is not given, it would import all by default. condition_check_block is for checking before making the import

ToDos

• Tests.. since I don't have time to write test case for this project yet.
• Due to the lazy-loading of model in rails, you need to specifically specify the model in rails. Like in the Review class above, it's reference to Article (to make sure that Article class is loaded before Review)
• Auto generation of mapping

Contributing to elasticsearch-rails-dynamic-json-support

• Check out the latest master to make sure the feature hasn't been implemented or the bug hasn't been fixed yet.
• Check out the issue tracker to make sure someone already hasn't requested it and/or contributed it.
• Fork the project.
• Start a feature/bugfix branch.
• Commit and push until you are happy with your contribution.
• Make sure to add tests for it. This is important so I don't break it in a future version unintentionally.
• Please try not to mess with the Rakefile, version, or history. If you want to have your own version, or is otherwise necessary, that is fine, but please isolate to its own commit so I can cherry-pick around it.

Copyright

Copyright (c) 2016 Song Yangyu. See LICENSE.txt for further details.