Add Nazrin::DataAccessor::Struct

[AMHOL]

This PR adds a Struct data-accessor, if the class that includes Nazrin::Searchable AND defines a domain_name config, the schema will be read using an AWS-Cloudsearch describe_index_fields call and data will be loaded from Cloudsearch and injected into the constructor when a search is made.

Example:

class User
  include Nazrin::Searchable

  searchable_configure do |config|
    config.domain_name = 'my-users-domain'
  end

  def initialize(attributes)
    @attributes = attributes
  end
end

User.search.query_parser('structured').query('matchall').execute

The schema is read and transformed into a mapping which looks like:

{
  'id' => 'int',
  'name' => 'text',
  'permissions' => 'literal-array'
}

If the response looks like:

{
  'data' => {
    'hits' => {
      'hit' => [
        {
          'id' => '1',
          'fields' => {
            'id' => ['1'],
            'name' => ['Joan'],
            'permissions' => ['admin']
          }
        }
      ]
    }
  }
}

It will result in a call like:

User.new('id' => '1', 'name' => 'Joan', 'permissions' => ['admin'])

[tsuwatch]

attr_accessor is preferable.

[tsuwatch]

It makes sense.
I would like to include Nazrin::Searchable, not Nazrin::Struct if possible.
But I have no idea yet.
Do you have any idea?

[AMHOL]

Perhaps we could make it the default data processor if the class doesn't descend from AR::Base or Mongoid::Document, but I like the idea of including Nazrin::Struct as it allows you to load the data from Cloudfront even when using AR or Mongo, if you choose to.

[tsuwatch]

I understand.
I think it is a little hard to expect the behavior, Struct is DataAccessor.
How about making a conditional branch with domain_name?

[AMHOL]

@tsuwatch I implemented what you asked here, I've also invited you as a collaborator on my fork, so if you're happy with those changes, feel free to merge the PR there and let me know if you want me to squash the commits / update the description in this PR.

[tsuwatch]

Please, squash commits, update description.

[AMHOL]

@tsuwatch done 😄

[AMHOL]

Thanks @tsuwatch 😄

[tsuwatch]

Merged, thank you so much!!! 😆