Search for empty string field in Sunspot (Solr)

In my model, I'm simply using something like:

class Person < ActiveRecord::Base
  searchable do
    string :middle_name
  end
end

The particular object I'm trying to search for has a :middle_name attribute that contains '', an empty string and is of the String datatype. Based on that information, I am assuming that Sunspot is also saving an empty string for that field in the Solr index.

After successfully doing Person.reindex and Sunspot.commit, I tried searching for the said object using Person.search{with(:middle_name, '')}.resultsin the rails console and it returns a 400 error in regards to Solr query syntax.

I then looked around and found some information on a query like Person.search{with(:middle_name, "* TO ''")}.results and Person.search{without(:middle_name, "* TO *")}.results, both of which return an empty set: [].

Anyone know a way that actually works and/or what the best way to do this is?

To make it work you have make monkey patch Sunspot::Query::Restriction::EqualTo method. Create a new file in config/initializers directory and add this code:

module Sunspot
    module Query
      module Restriction

          class EqualTo < Base
              def to_positive_boolean_phrase
                  case @value
                  when nil
                     "#{escape(@field.indexed_name)}:[* TO *]"
                  when ''
                     %Q(#{escape(@field.indexed_name)}:[* TO ""])
                  else
                     super
                  end
               end

               def negated?
                  if @value.nil?
                      !super
                  else
                      super
                  end
               end

               private

               def to_solr_conditional
                   "#{solr_value}"
               end

           end
       end
    end
end

Remember to restart rails server before you try this.