tests + fixes for using nil _id's

lib/mongo/collection.rb

@@ -175,7 +175,8 @@ module Mongo
     #   will be raised on an error. Checking for safety requires an extra
     #   round-trip to the database
     def save(to_save, options={})
-      if id = to_save[:_id] || to_save['_id']
+      if to_save.has_key?(:_id) || to_save.has_key?('_id')
+        id = to_save[:_id] || to_save['_id']
         update({:_id => id}, to_save, :upsert => true, :safe => options.delete(:safe))
         id
       else

lib/mongo/types/objectid.rb

@@ -44,7 +44,7 @@ module Mongo
 
     # Adds a primary key to the given document if needed.
     def self.create_pk(doc)
-      doc[:_id] || doc['_id'] ? doc : doc.merge!(:_id => self.new)
+      doc.has_key?(:_id) || doc.has_key?('_id') ? doc : doc.merge!(:_id => self.new)
     end
 
     # +data+ is an array of bytes. If nil, a new id will be generated.

test/test_collection.rb

@@ -53,6 +53,27 @@ class TestCollection < Test::Unit::TestCase
     assert_equal 5, @@db.collection("test.foo").find_one()["x"]
   end
 
+  def test_nil_id
+    assert_equal 5, @@test.insert({"_id" => 5, "foo" => "bar"}, {:safe => true})
+    assert_equal 5, @@test.save({"_id" => 5, "foo" => "baz"}, {:safe => true})
+    assert_equal nil, @@test.find_one("foo" => "bar")
+    assert_equal "baz", @@test.find_one(:_id => 5)["foo"]
+    assert_raise OperationFailure do
+      @@test.insert({"_id" => 5, "foo" => "bar"}, {:safe => true})
+    end
+
+    assert_equal nil, @@test.insert({"_id" => nil, "foo" => "bar"}, {:safe => true})
+    assert_equal nil, @@test.save({"_id" => nil, "foo" => "baz"}, {:safe => true})
+    assert_equal nil, @@test.find_one("foo" => "bar")
+    assert_equal "baz", @@test.find_one(:_id => nil)["foo"]
+    assert_raise OperationFailure do
+      @@test.insert({"_id" => nil, "foo" => "bar"}, {:safe => true})
+    end
+    assert_raise OperationFailure do
+      @@test.insert({:_id => nil, "foo" => "bar"}, {:safe => true})
+    end
+  end
+
   if @@version > "1.1"
     def test_distinct
       @@test.remove