Applying patch from 'Justas Butkus' to fix CakeSchema::compare()

Fixes issues with comparing null == '' and adds a new protected method to handle null aware array difference generation.
Tests added.
Fixes #1206

cake/libs/model/cake_schema.php

@@ -468,11 +468,11 @@ class CakeSchema extends Object {
 			if (!array_key_exists($table, $old)) {
 				$tables[$table]['add'] = $fields;
 			} else {
-				$diff = array_diff_assoc($fields, $old[$table]);
+				$diff = $this->_arrayDiffAssoc($fields, $old[$table]);
 				if (!empty($diff)) {
 					$tables[$table]['add'] = $diff;
 				}
-				$diff = array_diff_assoc($old[$table], $fields);
+				$diff = $this->_arrayDiffAssoc($old[$table], $fields);
 				if (!empty($diff)) {
 					$tables[$table]['drop'] = $diff;
 				}
@@ -480,7 +480,7 @@ class CakeSchema extends Object {
 
 			foreach ($fields as $field => $value) {
 				if (isset($old[$table][$field])) {
-					$diff = array_diff_assoc($value, $old[$table][$field]);
+					$diff = $this->_arrayDiffAssoc($value, $old[$table][$field]);
 					if (!empty($diff) && $field !== 'indexes' && $field !== 'tableParameters') {
 						$tables[$table]['change'][$field] = array_merge($old[$table][$field], $diff);
 					}
@@ -520,6 +520,46 @@ class CakeSchema extends Object {
 		return $tables;
 	}
 
+/**
+ * Extended array_diff_assoc noticing change from/to NULL values
+ *
+ * It behaves almost the same way as array_diff_assoc except for NULL values: if
+ * one of the values is not NULL - change is detected. It is useful in situation
+ * where one value is strval('') ant other is strval(null) - in string comparing
+ * methods this results as EQUAL, while it is not.
+ *
+ * @param array $array1 Base array
+ * @param array $array2 Corresponding array checked for equality
+ * @return array Difference as array with array(keys => values) from input array
+ *     where match was not found.
+ * @access protected
+ */
+	function _arrayDiffAssoc($array1, $array2) {
+		$difference = array();
+		foreach ($array1 as $key => $value) {
+			if (!array_key_exists($key, $array2)) {
+				$difference[$key] = $value;
+				continue;
+			}
+			$correspondingValue = $array2[$key];
+			if (is_null($value) !== is_null($correspondingValue)) {
+				$difference[$key] = $value;
+				continue;
+			}
+			if (is_bool($value) !== is_bool($correspondingValue)) {
+				$difference[$key] = $value;
+				continue;
+			}
+			$value = strval($value);
+			$correspondingValue = strval($correspondingValue);
+			if ($value === $correspondingValue) {
+				continue;
+			}
+			$difference[$key] = $value;
+		}
+		return $difference;
+	}
+
 /**
  * Formats Schema columns from Model Object
  *
@@ -596,7 +636,7 @@ class CakeSchema extends Object {
 		if (!is_array($new) || !is_array($old)) {
 			return false;
 		}
-		$change = array_diff_assoc($new, $old);
+		$change = $this->_arrayDiffAssoc($new, $old);
 		return $change;
 	}
 
@@ -614,12 +654,12 @@ class CakeSchema extends Object {
 
 		$add = $drop = array();
 
-		$diff = array_diff_assoc($new, $old);
+		$diff = $this->_arrayDiffAssoc($new, $old);
 		if (!empty($diff)) {
 			$add = $diff;
 		}
 
-		$diff = array_diff_assoc($old, $new);
+		$diff = $this->_arrayDiffAssoc($old, $new);
 		if (!empty($diff)) {
 			$drop = $diff;
 		}

cake/tests/cases/libs/model/cake_schema.test.php

@@ -798,6 +798,35 @@ class CakeSchemaTest extends CakeTestCase {
 		$this->assertEqual($expected, $compare);
 	}
 
+/**
+ * test comparing '' and null and making sure they are different.
+ *
+ * @return void
+ */
+	function testCompareEmptyStringAndNull() {
+		$One =& new CakeSchema(array(
+			'posts' => array(
+				'id' => array('type' => 'integer', 'null' => false, 'default' => NULL, 'key' => 'primary'),
+				'name' => array('type' => 'string', 'null' => false, 'default' => '')
+			)
+		));
+		$Two =& new CakeSchema(array(
+			'posts' => array(
+				'id' => array('type' => 'integer', 'null' => false, 'default' => NULL, 'key' => 'primary'),
+				'name' => array('type' => 'string', 'null' => false, 'default' => null)
+			)
+		));
+		$compare = $One->compare($Two);
+		$expected = array(
+			'posts' => array(
+				'change' => array(
+					'name' => array('type' => 'string', 'null' => false, 'default' => null)
+				)
+			)
+		);
+		$this->assertEqual($expected, $compare);
+	}
+
 /**
  * Test comparing tableParameters and indexes.
  *