Fixed $hint and $explain support.

lib/mongo/cursor.rb

@@ -125,13 +125,15 @@ module XGen
 
         # Returns an explain plan record.
         def explain
-          sel = OrderedHash.new
+          old_val = @query.explain
-          sel['query'] = @query.selector
+          @query.explain = true
-          sel['$explain'] = true
+
-          c = Cursor.new(@db, @collection, Query.new(sel))
+          c = Cursor.new(@db, @collection, @query)
-          e = c.next_object
+          explanation = c.next_object
           c.close
-          e
+
+          @query.explain = old_val
+          explanation
         end
 
         # Close the cursor.
@@ -210,18 +212,11 @@ module XGen
           # Run query first time we request an object from the wire
           unless @query_run
             hints = @hint_fields || @collection.hint_fields
-            query = if hints
+            old_hints = @query.hint_fields
-                      h = {}
+            @query.hint_fields = hints
-                      hints.each { |field| h[field] = 1 }
+            @db.send_query_message(QueryMessage.new(@db.name, @collection.name, @query))
-                      sel = OrderedHash.new
-                      sel['query'] = @query.selector
-                      sel['$hint'] = h
-                      Query.new(sel)
-                    else
-                      @query
-                    end
-            @db.send_query_message(QueryMessage.new(@db.name, @collection.name, query))
             @query_run = true
+            @query.hint_fields = old_hints
             read_all
           end
         end

lib/mongo/message/query_message.rb

@@ -18,9 +18,10 @@ module XGen
           write_int(query.number_to_skip)
           write_int(query.number_to_return)
           sel = query.selector
-          if query.order_by && query.order_by.length > 0
+          if query.contains_special_fields
             sel = OrderedHash.new
             sel['query'] = query.selector
+            if query.order_by && query.order_by.length > 0
               sel['orderby'] = case query.order_by
                                when String
                                  {query.order_by => 1}
@@ -33,6 +34,15 @@ module XGen
                                else
                                  raise "illegal order_by: is a #{query.order_by.class.name}, must be String, Array, Hash, or OrderedHash"
                                end
+            end
+            if query.hint_fields && query.hint_fields.length > 0
+              hints = OrderedHash.new
+              query.hint_fields.each { |hf| hints[hf] = 1 }
+              sel['$hint'] = hints
+            end
+            if query.explain
+              sel['$explain'] = true
+            end
                                
           end
           write_doc(sel)

lib/mongo/query.rb

@@ -27,6 +27,10 @@ module XGen
       class Query
 
         attr_accessor :number_to_skip, :number_to_return, :order_by
+        # If true, $explain will be set in QueryMessage that uses this query.
+        attr_accessor :explain
+        # Either +nil+ or an array of hint field names.
+        attr_accessor :hint_fields
         attr_reader :selector   # writer defined below
 
         # sel :: A hash describing the query. See the Mongo docs for details.
@@ -97,6 +101,10 @@ module XGen
             nil
           end
         end
+
+        def contains_special_fields
+          (@order_by != nil && @order_by.length > 0) || @explain || @hint_fields
+        end
       end
     end
   end