setting defaults in the DBO so you do not need to pass every field possible to avoid errors. also adds a test for calling with some missing fields. fixes #1779

lib/Cake/Model/Datasource/DboSource.php

@@ -194,6 +194,23 @@ class DboSource extends DataSource {
 		'rollback' => 'ROLLBACK'
 	);
 
+/**
+ * Default fields that are used by the DBO
+ *
+ * @var array
+ */	
+	protected $_queryDefaults = array(
+		'conditions' => array(),
+		'fields' => null,
+		'table' => null,
+		'alias' => null,
+		'order' => null,
+		'limit' => null,
+		'joins' => array(),
+		'group' => null,
+		'offset' => null
+	);
+
 /**
  * Separator string for virtualField composition
  *
@@ -1665,7 +1682,7 @@ class DboSource extends DataSource {
  * @see DboSource::renderStatement()
  */
 	public function buildStatement($query, $model) {
-		$query = array_merge(array('offset' => null, 'joins' => array()), $query);
+		$query = array_merge($this->_queryDefaults, $query);
 		if (!empty($query['joins'])) {
 			$count = count($query['joins']);
 			for ($i = 0; $i < $count; $i++) {

lib/Cake/Test/Case/Model/Datasource/DboSourceTest.php

@@ -843,4 +843,27 @@ class DboSourceTest extends CakeTestCase {
 		$log = $db->getLog();
 		$this->assertEquals($expected, $log['log'][0]);
 	}
+	
+/**
+ * Test build statement with some fields missing 
+ * 
+ * @return void
+ */
+	public function testBuildStatementDefaults() {
+		$conn = $this->getMock('MockPDO');
+		$db = new DboTestSource;
+		$db->setConnection($conn);
+		$subQuery = $db->buildStatement(
+			array(
+				'fields' => array('DISTINCT(AssetsTag.asset_id)'),
+				'table' => "assets_tags",
+				'alias'=>"AssetsTag",                                          
+				'conditions' => array("Tag.name"=>'foo bar'),
+				'limit' => null,         
+				'group' => "AssetsTag.asset_id"
+			),
+			$this->Model
+		);
+	}
+	
 }