add DB#last_status method

lib/mongo/db.rb

@@ -267,22 +267,19 @@ module Mongo
 
     # Returns the error message from the most recently executed database
     # operation for this connection, or +nil+ if there was no error.
-    #
-    # Note: as of this writing, errors are only detected on the db server
-    # for certain kinds of operations (writes). The plan is to change this
-    # so that all operations will set the error if needed.
     def error
       doc = db_command(:getlasterror => 1)
       raise "error retrieving last error: #{doc}" unless ok?(doc)
       doc['err']
     end
 
+    # Get status information from the last operation on this connection.
+    def last_status
+      db_command(:getlasterror => 1)
+    end
+
     # Returns +true+ if an error was caused by the most recently executed
     # database operation.
-    #
-    # Note: as of this writing, errors are only detected on the db server
-    # for certain kinds of operations (writes). The plan is to change this
-    # so that all operations will set the error if needed.
     def error?
       error != nil
     end

test/test_db.rb

@@ -176,6 +176,17 @@ class DBTest < Test::Unit::TestCase
     assert_nil @@db.previous_error
   end
 
+  def test_last_status
+    @@db['test'].clear
+    @@db['test'].save("i" => 1)
+
+    @@db['test'].update({"i" => 1}, {"$set" => {"i" => 2}})
+    assert @@db.last_status()["updatedExisting"]
+
+    @@db['test'].update({"i" => 1}, {"$set" => {"i" => 500}})
+    assert !@@db.last_status()["updatedExisting"]
+  end
+
   def test_text_port_number
     db = DB.new('ruby-mongo-test', [[@@host, @@port.to_s]])
     # If there is no error, all is well