Extract cascading deletes into the association classes.

Doing this allows each association to handle cascading deletes in their
own way. I think this makes the code cleaner, and allows userland
associations to participate in cascading deletes. In addition a new
trait has been extract to avoid inheritance/code duplication in
HasOne/HasMany.

Cake/ORM/Association.php

@@ -16,6 +16,7 @@
  */
 namespace Cake\ORM;
 
+use Cake\ORM\Entity;
 use Cake\ORM\Table;
 use Cake\ORM\TableRegistry;
 
@@ -415,4 +416,16 @@ public function transformRow($row) {
  * @return string|array|boolean
  */
 	protected abstract function _joinCondition(array $options);
+
+/**
+ * Handles cascading a delete from an associated model.
+ *
+ * Each implementing class should handle the cascaded delete as
+ * required.
+ *
+ * @param Cake\ORM\Entity $entity The entity that started the cascaded delete.
+ * @return boolean Success
+ */
+	public abstract function cascadeDelete(Entity $entity);
+
 }

Cake/ORM/Association/BelongsTo.php

@@ -17,6 +17,7 @@
 namespace Cake\ORM\Association;
 
 use Cake\ORM\Association;
+use Cake\ORM\Entity;
 use Cake\ORM\Query;
 use Cake\Utility\Inflector;
 
@@ -52,6 +53,18 @@ public function foreignKey($key = null) {
 		return parent::foreignKey($key);
 	}
 
+/**
+ * Handle cascading deletes.
+ *
+ * BelongsTo associations are never cleared in a cascading delete scenario.
+ *
+ * @param Cake\ORM\Entity $entity The entity that started the cascaded delete.
+ * @return boolean Success.
+ */
+	public function cascadeDelete(Entity $entity) {
+		return true;
+	}
+
 /**
  * Returns a single or multiple conditions to be appended to the generated join
  * clause for getting the results on the target table.

Cake/ORM/Association/BelongsToMany.php

@@ -17,6 +17,7 @@
 namespace Cake\ORM\Association;
 
 use Cake\ORM\Association;
+use Cake\ORM\Entity;
 use Cake\ORM\Query;
 use Cake\ORM\Table;
 use Cake\ORM\TableRegistry;
@@ -217,6 +218,25 @@ public function eagerLoader(array $options) {
 		return $this->_resultInjector($fetchQuery, $resultMap);
 	}
 
+/**
+ * Clear out the data in the join/pivot table for a given entity.
+ *
+ * @param Cake\ORM\Entity $entity The entity that started the cascading delete.
+ * @return boolean Success.
+ */
+	public function cascadeDelete(Entity $entity) {
+		$foreignKey = $this->foreignKey();
+		$primaryKey = $this->source()->primaryKey();
+		$conditions = [
+			$foreignKey => $entity->get($primaryKey)
+		];
+		// TODO fix multi-column primary keys.
+		$conditions = array_merge($conditions, $this->conditions());
+
+		$table = $this->pivot();
+		$table->deleteAll($conditions);
+	}
+
 /**
  * Appends any conditions required to load the relevant set of records in the
  * target table query given a filter key and some filtering values.

Cake/ORM/Association/DependentDeleteTrait.php

@@ -0,0 +1,56 @@
+<?php
+/**
+ * PHP Version 5.4
+ *
+ * CakePHP(tm) : Rapid Development Framework (http://cakephp.org)
+ * Copyright (c) Cake Software Foundation, Inc. (http://cakefoundation.org)
+ *
+ * Licensed under The MIT License
+ * For full copyright and license information, please see the LICENSE.txt
+ * Redistributions of files must retain the above copyright notice.
+ *
+ * @copyright     Copyright (c) Cake Software Foundation, Inc. (http://cakefoundation.org)
+ * @link          http://cakephp.org CakePHP(tm) Project
+ * @since         CakePHP(tm) v 3.0.0
+ * @license       MIT License (http://www.opensource.org/licenses/mit-license.php)
+ */
+namespace Cake\ORM\Association;
+
+use Cake\ORM\Entity;
+
+/**
+ * Implements cascading deletes for dependent associations.
+ *
+ * Included by HasOne and HasMany association classes.
+ */
+trait DependentDeleteTrait {
+
+/**
+ * Cascade a delete to remove dependent records.
+ *
+ * This method does nothing if the association is not dependent.
+ *
+ * @param Cake\ORM\Entity $entity The entity that started the cascaded delete.
+ * @return boolean Success.
+ */
+	public function cascadeDelete(Entity $entity) {
+		if (!$this->dependent()) {
+			return true;
+		}
+		$table = $this->target();
+		$foreignKey = $this->foreignKey();
+		$primaryKey = $this->source()->primaryKey();
+
+		$conditions = [
+			$foreignKey => $entity->get($primaryKey)
+		];
+		// TODO fix multi-column primary keys.
+		$conditions = array_merge($conditions, $this->conditions());
+
+		$query = $table->find('all')->where($conditions);
+		foreach ($query as $related) {
+			$table->delete($related, ['atomic' => false]);
+		}
+		return true;
+	}
+}

Cake/ORM/Association/HasMany.php

@@ -17,6 +17,8 @@
 namespace Cake\ORM\Association;
 
 use Cake\ORM\Association;
+use Cake\ORM\Association\DependentDeleteTrait;
+use Cake\ORM\Association\ExternalAssociationTrait;
 use Cake\ORM\Query;
 
 /**
@@ -28,6 +30,7 @@
 class HasMany extends Association {
 
 	use ExternalAssociationTrait;
+	use DependentDeleteTrait;
 
 /**
  * The type of join to be used when adding the association to a query

Cake/ORM/Association/HasOne.php

@@ -17,6 +17,7 @@
 namespace Cake\ORM\Association;
 
 use Cake\ORM\Association;
+use Cake\ORM\Association\DependentDeleteTrait;
 use Cake\ORM\Query;
 use Cake\Utility\Inflector;
 
@@ -28,6 +29,8 @@
  */
 class HasOne extends Association {
 
+	use DependentDeleteTrait;
+
 /**
  * Whether this association can be expressed directly in a query join
  *

Cake/ORM/Table.php

@@ -989,59 +989,11 @@ protected function _processDelete($entity, $options) {
 		}
 
 		foreach ($this->_associations as $assoc) {
-			// TODO Perhaps refactor the deletion into the association class?
-			if ($assoc->dependent()) {
-				$this->_deleteDependent($assoc, $entity);
-			} elseif ($assoc instanceof BelongsToMany) {
-				$this->_deletePivotRecords($assoc, $entity);
-			}
+			$assoc->cascadeDelete($entity);
 		}
 		return $success;
 	}
 
-/**
- * Delete data in any associations that are marked 'dependent'
- *
- * @param Cake\ORM\Association $assoc The association to clear.
- * @param Cake\ORM\Entity $entity The entity to delete dependent data for.
- * @return void
- */
-	protected function _deleteDependent(Association $assoc, Entity $entity) {
-		$table = $assoc->target();
-		$foreignKey = $assoc->foreignKey();
-		$primaryKey = $this->primaryKey();
-
-		$conditions = [
-			$foreignKey => $entity->get($primaryKey)
-		];
-		// TODO fix multi-column primary keys.
-		$conditions = array_merge($conditions, $assoc->conditions());
-
-		$query = $table->find('all')->where($conditions);
-		foreach ($query as $related) {
-			$table->delete($related, ['atomic' => false]);
-		}
-	}
-
-/**
- * Clear the data out of a BelongsToMany join table.
- *
- * @param Cake\ORM\Association\BelongsToMany $assoc The association to clear.
- * @param Cake\ORM\Entity $entity The entity to remove pivot records for.
- * @return void
- */
-	protected function _deletePivotRecords(BelongsToMany $assoc, Entity $entity) {
-		$foreignKey = $assoc->foreignKey();
-		$primaryKey = $this->primaryKey();
-		$conditions = [
-			$foreignKey => $entity->get($primaryKey)
-		];
-		// TODO fix multi-column primary keys.
-		$conditions = array_merge($conditions, $assoc->conditions());
-		$table = $assoc->pivot();
-		$table->deleteAll($conditions);
-	}
-
 /**
  * Calls a finder method directly and applies it to the passed query,
  * if no query is passed a new one will be created and returned

Cake/Test/TestCase/ORM/AssociationTest.php

@@ -52,7 +52,7 @@ public function setUp() {
 		];
 		$this->association = $this->getMock(
 			'\Cake\ORM\Association',
-			['_options', 'attachTo', '_joinCondition'],
+			['_options', 'attachTo', '_joinCondition', 'cascadeDelete'],
 			['Foo', $config]
 		);
 	}