previous_error and reset_error_history. snuck in a quick fix to OrderedHash equality

lib/mongo/db.rb

@@ -264,6 +264,27 @@ module XGen
           error != nil
         end
 
+        # Get the most recent error to have occured on this database
+        #
+        # Only returns errors that have occured since the last call to
+        # DB#reset_error_history - returns +nil+ if there is no such error.
+        def previous_error
+          error = db_command(:getpreverror => 1)
+          if error["err"]
+            error
+          else
+            nil
+          end
+        end
+
+        # Reset the error history of this database
+        #
+        # Calls to DB#previous_error will only return errors that have occurred
+        # since the most recent call to this method.
+        def reset_error_history
+          db_command(:reseterror => 1)
+        end
+
         # Returns true if this database is a master (or is not paired with any
         # other database), false if it is a slave.
         def master?

lib/mongo/util/ordered_hash.rb

@@ -21,9 +21,13 @@
 class OrderedHash < Hash
 
   def ==(other)
-    !other.nil? &&
-      keys == other.keys &&
-      values == other.values
+    begin
+      !other.nil? &&
+        keys == other.keys &&
+        values == other.values
+    rescue
+      false
+    end
   end
 
   # We only need the body of this class if the RUBY_VERSION is before 1.9

tests/test_db.rb

@@ -122,15 +122,33 @@ class DBTest < Test::Unit::TestCase
   end
 
   def test_error
-    doc = @@db.send(:db_command, :forceerror => 1)
-    assert @@db.error?
-    err = @@db.error
-    assert_match /forced error/, err
+    @@db.reset_error_history
+    assert_nil @@db.error
+    assert !@@db.error?
+    assert_nil @@db.previous_error
 
-    # ask again
+    @@db.send(:db_command, :forceerror => 1)
     assert @@db.error?
-    err2 = @@db.error
-    assert_equal err, err2
+    assert_not_nil @@db.error
+    assert_not_nil @@db.previous_error
+
+    @@db.send(:db_command, :forceerror => 1)
+    assert @@db.error?
+    assert @@db.error
+    prev_error = @@db.previous_error
+    assert_equal 1, prev_error['nPrev']
+    assert_equal prev_error["err"], @@db.error
+
+    @@db.collection('test').find_first
+    assert_nil @@db.error
+    assert !@@db.error?
+    assert @@db.previous_error
+    assert_equal 2, @@db.previous_error['nPrev']
+
+    @@db.reset_error_history
+    assert_nil @@db.error
+    assert !@@db.error?
+    assert_nil @@db.previous_error
   end
 
   def test_text_port_number