RUBY-790 Allow count to work with query hints

Author: estolfo

lib/mongo/collection.rb

@@ -202,8 +202,9 @@ def named_hint=(hint=nil)
     # @option opts [Array]   :sort an array of [key, direction] pairs to sort by. Direction should
     #   be specified as Mongo::ASCENDING (or :ascending / :asc) or Mongo::DESCENDING (or :descending / :desc)
     # @option opts [String, Array, OrderedHash] :hint hint for query optimizer, usually not necessary if
-    #   using MongoDB > 1.1
-    # @option opts [String] :named_hint for specifying a named index as a hint, will be overriden by :hint
+    #   using MongoDB > 1.1. Note that if using hint with count, there is inconsistent behavior with hints
+    #   specified as documents. Use named_hint for reliable behavior with count. Please see SERVER-15107.
+    # @option opts [String] :named_hint for specifying a named index as a hint, will be overridden by :hint
     #   if :hint is also provided.
     # @option opts [Boolean] :snapshot (false) if true, snapshot mode will be used for this query.
     #   Snapshot mode assures no duplicates are returned, or objects missed, which were preset at both the start and
@@ -1030,17 +1031,24 @@ def stats
     # @option opts [Hash] :query ({}) A query selector for filtering the documents counted.
     # @option opts [Integer] :skip (nil) The number of documents to skip.
     # @option opts [Integer] :limit (nil) The number of documents to limit.
+    # @option opts [String, Array, OrderedHash] :hint hint for query optimizer, usually not necessary if
+    #   using MongoDB > 1.1. Note that there is inconsistent behavior with hints
+    #   specified as documents. Use named_hint for reliable behavior with count. Please see SERVER-15107.
+    # @option opts [String] :named_hint for specifying a named index as a hint, will be overridden by :hint
+    #   if :hint is also provided.
     # @option opts [:primary, :secondary] :read Read preference for this command. See Collection#find for
     #  more details.
     # @option opts [String]  :comment (nil) a comment to include in profiling logs
     #
     # @return [Integer]
     def count(opts={})
       find(opts[:query],
-           :skip  => opts[:skip],
-           :limit => opts[:limit],
-           :read  => opts[:read],
-           :comment => opts[:comment]).count(true)
+           :skip       => opts[:skip],
+           :limit      => opts[:limit],
+           :hint       => opts[:hint],
+           :named_hint => opts[:named_hint],
+           :read       => opts[:read],
+           :comment    => opts[:comment]).count(true)
     end
 
     alias :size :count

lib/mongo/cursor.rb

@@ -204,6 +204,7 @@ def count(skip_and_limit = false)
       end
 
       command.merge!(BSON::OrderedHash["fields", @fields])
+      command.merge!(BSON::OrderedHash["hint", @hint]) if @hint
 
       response = @db.command(command, :read => @read, :comment => @comment)
       return response['n'].to_i if Mongo::Support.ok?(response)

test/functional/collection_test.rb

@@ -1008,6 +1008,40 @@ def test_count
     assert_equal 0, @test.count(:skip => 2)
   end
 
+  # @todo: change to test the :hint option when SERVER-15107 is fixed
+  # Right now, only hints specified as strings will work.
+  # The Ruby driver changes a :hint string to a document.
+  # We must therefore test using the :named_hint option.
+  def test_count_with_hint
+    @test.drop
+    @test.save(:i => 1)
+    @test.save(:i => 2)
+
+    assert_equal 2, @test.count
+    assert_equal 1, @test.count(:query => { :i => 1 }, :named_hint => '_id_')
+    assert_equal 2, @test.count(:query => { }, :named_hint => '_id_')
+
+    @test.ensure_index(BSON::OrderedHash[:i, Mongo::ASCENDING])
+
+    if @version > '2.6'
+      assert_raise Mongo::OperationFailure do
+        @test.count(:query => { :i => 1 }, :named_hint => 'bad_hint')
+      end
+    else
+      assert_equal 1, @test.count(:query => { :i => 1 }, :named_hint => 'bad_hint')
+    end
+
+    @test.ensure_index(BSON::OrderedHash[:x, Mongo::ASCENDING], :sparse => true)
+
+    if @version > '2.6'
+      assert_equal 0, @test.count(:query => { :i => 1 }, :named_hint => 'x_1')
+    else
+      assert_equal 1, @test.count(:query => { :i => 1 }, :named_hint => 'x_1')
+    end
+
+    assert_equal 2, @test.count(:query => { }, :named_hint => 'x_1')
+  end
+
   # Note: #size is just an alias for #count.
   def test_size
     @test.drop

test/functional/cursor_test.rb

@@ -534,6 +534,40 @@ def test_count_with_fields
     end
   end
 
+  # @todo: change to test the :hint option when SERVER-15107 is fixed
+  # Right now, only hints specified as strings will work.
+  # The Ruby driver changes a :hint string to a document.
+  # We must therefore test using the :named_hint option.
+  def test_count_with_hint
+    @coll.drop
+    @coll.save(:i => 1)
+    @coll.save(:i => 2)
+
+    assert_equal 2, @coll.find.count
+    assert_equal 1, @coll.find({ :i => 1 }, :named_hint => '_id_').count
+    assert_equal 2, @coll.find({ }, :named_hint => '_id_').count
+
+    @coll.ensure_index(BSON::OrderedHash[:i, Mongo::ASCENDING])
+
+    if @version > '2.6'
+      assert_raise Mongo::OperationFailure do
+        @coll.find({ :i => 1 }, :named_hint => 'bad_hint').count
+      end
+    else
+      assert_equal 1, @coll.find({ :i => 1 }, :named_hint => 'bad_hint').count
+    end
+
+    @coll.ensure_index(BSON::OrderedHash[:x, Mongo::ASCENDING], :sparse => true)
+
+    if @version > '2.6'
+      assert_equal 0, @coll.find({ :i => 1 }, :named_hint => 'x_1').count
+    else
+      assert_equal 1, @coll.find({ :i => 1 }, :named_hint => 'x_1').count
+    end
+
+    assert_equal 2, @coll.find({ }, :named_hint => 'x_1').count
+  end
+
   def test_has_next
     @coll.remove
     200.times do |n|