[karmi#222] Added a prefix query

See: http://www.elasticsearch.org/guide/reference/query-dsl/prefix-query.html

Closes karmi#222

lib/tire/search/query.rb

@@ -34,6 +34,14 @@ def string(value, options={})
         @value
       end
 
+      def prefix(field, value, options={})
+        if options[:boost]
+          @value = { :prefix => { field => { :prefix => value, :boost => options[:boost] } } }
+        else
+          @value = { :prefix => { field => value } }
+        end
+      end
+
       def custom_score(options={}, &block)
         @custom_score ||= Query.new(&block)
         @value[:custom_score] = options

test/integration/prefix_query_test.rb

@@ -0,0 +1,43 @@
+require 'test_helper'
+
+module Tire
+
+  class PrefixQueryTest < Test::Unit::TestCase
+    include Test::Integration
+
+    context "Prefix queries" do
+
+      should "search by a prefix" do
+        s = Tire.search('articles-test') do
+          query do
+            # "on" => "One"
+            prefix :title, "on"
+          end
+        end
+
+        assert_equal 1, s.results.size
+        assert_equal ['One'], s.results.map(&:title)
+      end
+
+      should "allow to specify boost" do
+        s = Tire.search('articles-test') do
+          query do
+            boolean do
+              # "on" => "One", boost it
+              should { prefix :title, "on", :boost => 2.0 }
+              should { all }
+            end
+          end
+          sort { by :_score }
+        end
+
+        assert_equal 5, s.results.size
+        assert_equal 'One', s.results.first.title
+
+      end
+
+    end
+
+  end
+
+end

test/unit/search_query_test.rb

@@ -236,6 +236,17 @@ class QueryTest < Test::Unit::TestCase
         end
       end
 
+      context "Prefix query" do
+        should "allow search for a prefix" do
+          assert_equal( { :prefix => { :user => "foo" } }, Query.new.prefix(:user, "foo") )
+        end
+
+        should "allow setting boost for prefix" do
+          assert_equal( { :prefix => {:user => {:prefix => "foo", :boost => 2.0 } } },
+                        Query.new.prefix(:user, "foo", :boost => 2.0) )
+        end
+      end
+
     end
   end