Solr is a search server based on lucene java search library with a HTTP/XML interface. Using Solr, large collections of documents can be indexed based on strongly typed field definitions, thereby taking advantage of Lucene's powerful full-text search features.

acts_as_solr is a ruby on rails plugin adding Solr capabilities to activerecord models. It hides all configuration and manual setting efforts with Solr and provides you with simple find_by... methods. acts_as_solr can be used as a replacement to acts_as_ferret because of inbuilt full text search capabilities ;-) . The purpose of this article is to explain acts_as_solr with examples.

Installation: Installation is well explained on acts_as_solr homepage and getting started with acts_as_solr

Note: acts_as_solr requires jre1.5 on system. Before running any of the solr methods make sure you start solr server with rake solr:start command.

Our example model for this tutorial will be DigitalCamera [classname: Camera] with following fields

• name (type:string)
• brand (type:string) [we want faceted browsing on this field]
• resolution (type:float) [we want faceted browsing on this field]
• other fields which we do not want to index

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class Camera
  acts_as_solr :fields=>[:name,:brand,:resolution]
end

@results = Camera.find_by_solr("canon powershot")

• limit: to limit the count of search results
• offset: starting index of the search results.
• scores: solr scores for each of the result returned
• order: by which field results should be ordered and in asc/desc order?
• operator: words in query should be separated by "and" or "or" i.e. all words should exist in matching results or any of the words respectively

• If you do not want Camera models objects as results, you can use find_id_by_solr which will return just id's from the Camera table (score option is not supported yet)
• The result of find_by_solr is not an array of camera objects. Its a ActsAsSolr::SearchResults object.

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@products = @results.docs
@total_hits = @results.total_hits

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<%= will_paginate WillPaginate::Collection.new((params[:page]||1),
                                                         (params[:products_per_page]||10),@total_hits) -%>

Presentation by Keith Instone is an excellent read on faceted browsing with examples.

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class Camera
  acts_as_solr :fields=>[:name,:brand,:resolution], 
               :facets=>[:brand,:resolution]
end

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class Camera
  acts_as_solr :fields=>[:name,:brand,{:resolution=>:range_float}], 
                :facets=>[:brand,:resolution]
end

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@results = Camera.find_by_solr("powershot",{:facets=>
                                            {:zeros=>false,:fields=>[:brand]}})

• :zeros parameter tells solr not to return the brand values whose facet count is zero.
• @results.facets["facet_fields"]["brand_facet"] contains the names of brand with the corresponding counts. A sample result:

  {"Canon USA"=>1, "Canon PowerShot"=>1, "Canon"=>91}

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# INCORRECT
@results = Camera.find_by_solr("powershot",{:facets=>
                                            {:zeros=>false,:fields=>[:brand,:resolution]}}) 

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@results = Camera.find_by_solr("powershot",
                             {:facets=>{:zeros=>false,
                                        :fields=>[:brand],
                                        :query=>["resolution:[0 TO 4]","resolution:[5 TO 9]",
                                                    "resolution:[10 TO 14]","resolution:[15 TO 20]"]
                                              }
                              })

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@results = Camera.find_by_solr("powershot"+" AND resolution:[0 TO 4]",
                         {:facets=>{:zeros=>false, :fields=>[:brand]}}) 
## resolution queries has been removed since you already made a selection in resolution itself.

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@results = Camera.find_by_solr(query,{:facets=>
                                  {:zeros=>false,
                                    :query=>["resolution:[0 TO 4]", "resolution:[5 TO 9]",
                                            "resolution:[10 TO 14]", "resolution:[15 TO 20]"],
                                    :browse=>["brand:Canon"]}
                                  })

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acts_as_solr :fields=>[:name,{:brand=>:facet}, {:resolution=>:range_float}], 
           :facets=>[:brand,:resolution]

acts_as_solr :fields => [{:name=>{:boost=>2}},:brand,:resolution]

• How to search solr with no query or 'nil' query. i.e. Product pages with navigation without a search query. Use query = "[* TO *]"

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  @results = Camera.find_by_solr("[* TO *]", {:facets=>{:zeros=>false, :fields=>[:brand], :query=>["resolution:[0 TO 4]", "resolution:[5 TO 9]", "resolution:[10 TO 14]", "resolution:[15 TO 20]"] } })

• Already have database, how to integrate solr now? Goto ./script/console and run

  Camera.rebuild_solr_index

• Adding or updating rows to table automatically adds/modifies them in table.
• If you have already created index on solr (not acts_as_solr), it will not work with acts_as_solr. This is because, in solr configuration, schema.xml tells the solr exactly about the columns you are going to index, their data types. But, with acts_as_solr you never modify schema.xml. Actually, acts_as_solr uses dynamic fields to tell solr about the fields and their data types. So, acts_as_solr does not finds anything in your already created index because field names are no more same.

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class Test::Unit::TestCase
  begin
    Net::HTTP.get_response(URI.parse('http://localhost:8981/solr/'))
  rescue Errno::ECONNREFUSED
    raise "You forgot to 'rake solr:start RAILS_ENV=test', foo!"
  end 

  def self.fixtures(*table_names)
    if block_given?
      Fixtures.create_fixtures(Test::Unit::TestCase.fixture_path, table_names) { yield }
    else
      Fixtures.create_fixtures(Test::Unit:: TestCase.fixture_path, table_names)
    end
    table_names.each do |table_name|
      clear_from_solr(table_name)
      klass = instance_eval table_name.to_s.capitalize.singularize.camelize
      klass.find (:all).each{|content| content.solr_save}
    end
  end

  private
  def self.clear_from_solr(table_name)
    ActsAsSolr::Post.execute(Solr::Request::Delete.new(:query => "type_t:#{table_name.to_s.capitalize.singularize.camelize}")
  end
end

1. removed top lines
2. added camelize for removing "_" from model names
3. added lines to test presence of test server running .. (from google groups)

• acts_as_solr benchmark results
• acts_as_solr performance on some live site
• http://www.webdesignpractices.com/navigation/facets.html
• http://cfis.savagexi.com/articles/2007/07/10/how-to-profile-your-rails-application
• Deploying acts_as_solr on tomcat