Improve belongsTo and hasOne for unneeded queries when recursive > 1.

Reuse already joined data for 'belongsTo' and 'hasOne' associations instead of running unneeded queries for each record.
Fixes #47

lib/Cake/Model/Datasource/DboSource.php

@@ -1080,6 +1080,7 @@ public function read(Model $model, $queryData = array(), $recursive = null) {
 		$query = trim($this->generateAssociationQuery($model, null, null, null, null, $queryData, false, $null));
 
 		$resultSet = $this->fetchAll($query, $model->cacheQueries);
+
 		if ($resultSet === false) {
 			$model->onError();
 			return false;
@@ -1092,6 +1093,10 @@ public function read(Model $model, $queryData = array(), $recursive = null) {
 		}
 
 		if ($model->recursive > -1) {
+			$joined = array();
+			if (isset($queryData['joins'][0]['alias'])) {
+				$joined[$model->alias] = (array)Hash::extract($queryData['joins'], '{n}.alias');
+			}
 			foreach ($_associations as $type) {
 				foreach ($model->{$type} as $assoc => $assocData) {
 					$linkModel = $model->{$assoc};
@@ -1108,6 +1113,7 @@ public function read(Model $model, $queryData = array(), $recursive = null) {
 
 					if (isset($db) && method_exists($db, 'queryAssociation')) {
 						$stack = array($assoc);
+						$stack['joined'] = $joined;
 						$db->queryAssociation($model, $linkModel, $type, $assoc, $assocData, $array, true, $resultSet, $model->recursive - 1, $stack);
 						unset($db);
 
@@ -1176,6 +1182,11 @@ protected function _filterResults(&$results, Model $model, $filtered = array())
  * @throws CakeException when results cannot be created.
  */
 	public function queryAssociation(Model $model, &$linkModel, $type, $association, $assocData, &$queryData, $external, &$resultSet, $recursive, $stack) {
+		if (isset($stack['joined'])) {
+			$joined = $stack['joined'];
+			unset($stack['joined']);
+		}
+
 		if ($query = $this->generateAssociationQuery($model, $linkModel, $type, $association, $assocData, $queryData, $external, $resultSet)) {
 			if (!is_array($resultSet)) {
 				throw new CakeException(__d('cake_dev', 'Error in Model %s', get_class($model)));
@@ -1251,10 +1262,17 @@ public function queryAssociation(Model $model, &$linkModel, $type, $association,
 			foreach ($resultSet as &$row) {
 				if ($type !== 'hasAndBelongsToMany') {
 					$q = $this->insertQueryData($query, $row, $association, $assocData, $model, $linkModel, $stack);
+					$fetch = null;
 					if ($q !== false) {
-						$fetch = $this->fetchAll($q, $model->cacheQueries);
-					} else {
-						$fetch = null;
+						$joinedData = array();
+						if (($type === 'belongsTo' || $type === 'hasOne') && isset($row[$linkModel->alias], $joined[$model->alias]) && in_array($linkModel->alias, $joined[$model->alias])) {
+							$joinedData = Hash::filter($row[$linkModel->alias]);
+							if (!empty($joinedData)) {
+								$fetch[0] = array($linkModel->alias => $row[$linkModel->alias]);
+							}
+						} else {
+							$fetch = $this->fetchAll($q, $model->cacheQueries);
+						}
 					}
 				}
 				$selfJoin = $linkModel->name === $model->name;