diff --git a/AbstractPropertyAccessor.php b/AbstractPropertyAccessor.php
index d1b9b09..2fef975 100644
--- a/AbstractPropertyAccessor.php
+++ b/AbstractPropertyAccessor.php
@@ -16,64 +16,6 @@
 abstract class AbstractPropertyAccessor implements \ArrayAccess, \IteratorAggregate
 {
 
-	/**
-	 * ArrayAccess::offsetSet()
-	 *
-	 * @param mixed
-	 * @param mixed
-	 */
-	public function offsetSet($name, $value)
-	{
-		if (!property_exists($this, $name)) {
-			throw new \InvalidArgumentException(
-				sprintf('The attribute "%s" does not exists.', $name)
-			);
-		}
-		return $this->{$name} = $value;
-	}
-
-	/**
-	 * ArrayAccess::offsetGet()
-	 *
-	 * @param mixed
-	 * @return mixed
-	 */
-	public function offsetGet($name)
-	{
-		if (!property_exists($this, $name)) {
-			throw new \InvalidArgumentException(
-				sprintf('The attribute "%s" does not exists.', $name)
-			);
-		}
-		return $this->{$name};
-	}
-
-	/**
-	 * ArrayAccess::offsetUnset()
-	 *
-	 * @param mixed
-	 */
-	public function offsetUnset($name)
-	{
-		if (!property_exists($this, $name)) {
-			throw new \InvalidArgumentException(
-				sprintf('The attribute "%s" does not exists.', $name)
-			);
-		}
-		$this->{$name} = null;
-	}
-
-	/**
-	 * ArrayAccess::offsetExists()
-	 *
-	 * @param mixed
-	 * @return bool
-	 */
-	public function offsetExists($name)
-	{
-		return (property_exists($this, $name) && !is_null($this->{$name}));
-	}
-
 	/**
 	 * 引数なしの場合は全てのプロパティを配列で返します。
 	 * 引数ありの場合は全てのプロパティを引数の配列からセットして$thisを返します。
@@ -90,10 +32,20 @@ public function properties()
 			$properties = func_get_arg(0);
 			if (!is_array($properties) && !($properties instanceof \Traversable)) {
 				throw new \InvalidArgumentException(
-					'The properties is not Array and not Traversable.');
+					sprintf('The properties is not an Array and not Traversable. type:%s',
+						is_object($properties)
+							? get_class($properties)
+							: gettype($properties)
+					)
+				);
 			}
 			foreach ($properties as $name => $value) {
-				$this->offsetSet($name, $value);
+				if (!property_exists($this, $name)) {
+					throw new \InvalidArgumentException(
+						sprintf('The property "%s" does not exists.', $name)
+					);
+				}
+				$this->{$name} = $value;
 			}
 			return $this;
 		}
@@ -101,38 +53,45 @@ public function properties()
 	}
 
 	/**
-	 * IteratorAggregate::getIterator()
+	 * ArrayAccess::offsetExists()
 	 *
-	 * @return \ArrayIterator
+	 * @param string プロパティ名
+	 * @return bool
 	 */
-	public function getIterator()
+	public function offsetExists($name)
 	{
-		return new \ArrayIterator($this->properties());
+		return (property_exists($this, $name) && $this->{$name} !== null);
 	}
 
 	/**
-	 * 配列に変換して返します。
+	 * __isset
 	 *
-	 * @return array
+	 * @param string プロパティ名
+	 * @return bool
 	 */
-	public function toArray()
+	public function __isset($name)
 	{
-		return $this->properties();
+		return $this->offsetExists($name);
 	}
 
 	/**
-	 * magic setter
+	 * ArrayAccess::offsetGet()
 	 *
 	 * @param string プロパティ名
-	 * @param mixed プロパティ値
+	 * @return mixed
 	 */
-	public function __set($name, $value)
+	public function offsetGet($name)
 	{
-		$this->offsetSet($name, $value);
+		if (!property_exists($this, $name)) {
+			throw new \InvalidArgumentException(
+				sprintf('The property "%s" does not exists.', $name)
+			);
+		}
+		return $this->{$name};
 	}
 
 	/**
-	 * magic getter
+	 * __get
 	 *
 	 * @param string プロパティ名
 	 */
@@ -142,18 +101,49 @@ public function __get($name)
 	}
 
 	/**
-	 * magic isset
+	 * ArrayAccess::offsetSet()
+	 *
+	 * @param mixed
+	 * @param mixed
+	 */
+	public function offsetSet($name, $value)
+	{
+		if (!property_exists($this, $name)) {
+			throw new \InvalidArgumentException(
+				sprintf('The property "%s" does not exists.', $name)
+			);
+		}
+		return $this->{$name} = $value;
+	}
+
+	/**
+	 * __set
 	 *
 	 * @param string プロパティ名
-	 * @return bool
+	 * @param mixed プロパティ値
 	 */
-	public function __isset($name)
+	public function __set($name, $value)
 	{
-		return $this->offsetExists($name);
+		$this->offsetSet($name, $value);
+	}
+
+	/**
+	 * ArrayAccess::offsetUnset()
+	 *
+	 * @param mixed
+	 */
+	public function offsetUnset($name)
+	{
+		if (!property_exists($this, $name)) {
+			throw new \InvalidArgumentException(
+				sprintf('The property "%s" does not exists.', $name)
+			);
+		}
+		$this->{$name} = null;
 	}
 
 	/**
-	 * magic unset
+	 * __unset
 	 *
 	 * @param string プロパティ名
 	 */
@@ -164,21 +154,44 @@ public function __unset($name)
 
 	/**
 	 * __toString
+	 *
+	 * @return string
 	 */
 	public function __toString()
 	{
 		return var_export($this->properties(), true);
 	}
 
+	/**
+	 * IteratorAggregate::getIterator()
+	 *
+	 * @return \ArrayIterator
+	 */
+	public function getIterator()
+	{
+		return new \ArrayIterator($this->properties());
+	}
+
 	/**
 	 * __sleep
 	 *
-	 * @param void
-	 * @return void
+	 * @return array
 	 */
 	public function __sleep()
 	{
-		return array_keys($this->properties(), true);
+		return array_keys($this->properties());
+	}
+
+	/**
+	 * __clone
+	 */
+	public function __clone()
+	{
+		foreach ($this->properties() as $name => $value) {
+			if (is_object($value)) {
+				$this->{$name} = clone $value;
+			}
+		}
 	}
 
 	/**
@@ -187,11 +200,21 @@ public function __sleep()
 	 * @param array
 	 * @return object
 	 */
-	public static function __set_state($attributes)
+	public static function __set_state($properties)
 	{
 		$instance = new static();
-		$instance->properties($attributes);
+		$instance->properties($properties);
 		return $instance;
 	}
 
+	/**
+	 * 配列に変換して返します。
+	 *
+	 * @return array
+	 */
+	public function toArray()
+	{
+		return $this->properties();
+	}
+
 }
diff --git a/Tests/AbstractPropertyAccessorTest.php b/Tests/AbstractPropertyAccessorTest.php
index 7c092d9..4bcbbd4 100644
--- a/Tests/AbstractPropertyAccessorTest.php
+++ b/Tests/AbstractPropertyAccessorTest.php
@@ -18,11 +18,14 @@
 class AbstractPropertyAccessorTest extends \PHPUnit_Framework_TestCase
 {
 
-	public function testOffsetSet()
+	public function testOffsetExists()
 	{
 		$test = new Test();
-		$test->offsetSet('string', 'Foo');
-		$this->assertEquals('Foo', $test->string);
+		$test->string = 'Foo';
+		$test->null = null;
+		$this->assertTrue($test->offsetExists('string'));
+		$this->assertFalse($test->offsetExists('null'));
+		$this->assertFalse($test->offsetExists('not_defined_property'));
 	}
 
 	public function testOffsetGet()
@@ -35,19 +38,26 @@ public function testOffsetGet()
 	/**
 	 * @expectedException \InvalidArgumentException
 	 */
-	public function testRaiseExceptionWhenSetUndefinedProperty()
+	public function testOffsetGetRaiseInvalidArgumentException()
 	{
 		$test = new Test();
-		$test->offsetSet('not_defined_attribute', 'Foo');
+		$test->offsetGet('not_defined_property');
+	}
+
+	public function testOffsetSet()
+	{
+		$test = new Test();
+		$test->offsetSet('string', 'Foo');
+		$this->assertEquals('Foo', $test->string);
 	}
 
 	/**
 	 * @expectedException \InvalidArgumentException
 	 */
-	public function testRaiseExceptionWhenGetUndefinedProperty()
+	public function testOffsetSetRaiseInvalidArgumentException()
 	{
 		$test = new Test();
-		$test->offsetGet('not_defined_attribute');
+		$test->offsetSet('not_defined_property', 'Foo');
 	}
 
 	public function testOffsetUnset()
@@ -59,25 +69,18 @@ public function testOffsetUnset()
 		$this->assertEmpty($test->string);
 	}
 
-	public function testOffsetExists()
-	{
-		$test = new Test();
-		$test->string = 'Foo';
-		$test->null = null;
-		$this->assertTrue($test->offsetExists('string'));
-		$this->assertFalse($test->offsetExists('null'));
-		$this->assertFalse($test->offsetExists('not_defined_attribute'));
-	}
-
 	public function testArrayAccess()
 	{
+		$now = new \DateTime();
 		$test = new Test();
 		$test['string' ] = 'Foo';
 		$test['null'   ] = null;
 		$test['boolean'] = true;
+		$test['datetime'] = $now;
 		$this->assertEquals('Foo', $test['string']);
 		$this->assertNull($test['null']);
 		$this->assertTrue($test['boolean']);
+		$this->assertSame($now, $test['datetime']);
 	}
 
 	public function testIssetArrayAccess()
@@ -87,7 +90,7 @@ public function testIssetArrayAccess()
 		$test->null = null;
 		$this->assertTrue(isset($test['string']));
 		$this->assertFalse(isset($test['null']));
-		$this->assertFalse(isset($test['not_defined_attribute']));
+		$this->assertFalse(isset($test['not_defined_property']));
 	}
 
 	public function testIssetPropertyAccess()
@@ -97,7 +100,7 @@ public function testIssetPropertyAccess()
 		$test->null = null;
 		$this->assertTrue(isset($test->string));
 		$this->assertFalse(isset($test->null));
-		$this->assertFalse(isset($test->not_defined_attribute));
+		$this->assertFalse(isset($test->not_defined_property));
 	}
 
 	public function testUnsetArrayAccess()
@@ -138,10 +141,12 @@ public function testIsNullPropertyAccess()
 
 	public function testTraversable()
 	{
+		$now = new \DateTime();
 		$test = new Test();
 		$test->string = 'Foo';
 		$test->null = null;
 		$test->boolean = true;
+		$test->datetime = $now;
 		foreach ($test as $name => $value) {
 			switch ($name) {
 			case 'string':
@@ -153,6 +158,9 @@ public function testTraversable()
 			case 'boolean':
 				$this->assertTrue($value);
 				break;
+			case 'datetime':
+				$this->assertSame($now, $value);
+				break;
 			}
 		}
 	}
@@ -163,7 +171,10 @@ public function testSerialize()
 		$test->string = 'Foo';
 		$test->null = null;
 		$test->boolean = true;
-		$this->assertEquals($test, unserialize(serialize($test)));
+		$test->datetime = new \DateTime();
+		$serialized = serialize($test);
+		$this->assertEquals($test, unserialize($serialized));
+		$this->assertNotSame($test, unserialize($serialized));
 	}
 
 	public function testVarExport()
@@ -172,8 +183,22 @@ public function testVarExport()
 		$test->string = 'Foo';
 		$test->null = null;
 		$test->boolean = true;
+		$test->datetime = new \DateTime();
 		eval('$exported = ' . var_export($test, true) . ';');
 		$this->assertEquals($test, $exported);
+		$this->assertNotSame($test, $exported);
+	}
+
+	public function testClone()
+	{
+		$test = new Test();
+		$test->string = 'Foo';
+		$test->null = null;
+		$test->boolean = true;
+		$test->datetime = new \DateTime();
+		$cloned = clone $test;
+		$this->assertEquals($test->datetime, $cloned->datetime);
+		$this->assertNotSame($test->datetime, $cloned->datetime);
 	}
 
 }
@@ -183,4 +208,5 @@ class Test extends AbstractPropertyAccessor
 	protected $string;
 	protected $null;
 	protected $boolean;
+	protected $datetime;
 }
diff --git a/composer.json b/composer.json
index 5ec8fdf..4b730f0 100644
--- a/composer.json
+++ b/composer.json
@@ -3,7 +3,7 @@
     "homepage": "https://github.com/k-holy/volcanus-database",
     "type": "library",
     "description": "database abstraction layer",
-    "version": "0.3.0",
+    "version": "0.3.1",
     "license": "MIT",
     "authors": [
         {