diff --git a/Cake/ORM/Association/BelongsToMany.php b/Cake/ORM/Association/BelongsToMany.php
index 241a99f7942..cce508ce70d 100644
--- a/Cake/ORM/Association/BelongsToMany.php
+++ b/Cake/ORM/Association/BelongsToMany.php
@@ -226,12 +226,14 @@ public function eagerLoader(array $options) {
  * @return boolean Success.
  */
 	public function cascadeDelete(Entity $entity, $options = []) {
-		$foreignKey = $this->foreignKey();
+		$foreignKey = (array)$this->foreignKey();
 		$primaryKey = $this->source()->primaryKey();
-		$conditions = [
-			$foreignKey => $entity->get($primaryKey)
-		];
-		// TODO fix multi-column primary keys.
+		$conditions = [];
+
+		if ($primaryKey) {
+			$conditions = array_combine($foreignKey, $entity->extract((array)$primaryKey));
+		}
+
 		$conditions = array_merge($conditions, $this->conditions());
 
 		$table = $this->pivot();
diff --git a/Cake/ORM/Table.php b/Cake/ORM/Table.php
index bbcc6e19118..b8e002988a1 100644
--- a/Cake/ORM/Table.php
+++ b/Cake/ORM/Table.php
@@ -95,7 +95,7 @@ class Table {
  *
  * @var string
  */
-	protected $_primaryKey = 'id';
+	protected $_primaryKey;
 
 /**
  * The name of the field that represents a human readable representation of a row
@@ -303,9 +303,22 @@ public function schema($schema = null) {
 			}
 			return $this->_schema;
 		}
+
 		if (is_array($schema)) {
+			$constraints = [];
+
+			if (isset($schema['_constraints'])) {
+				$constraints = $schema['_constraints'];
+				unset($schema['_constraints']);
+			}
+
 			$schema = new Schema($this->table(), $schema);
+
+			foreach ($constraints as $name => $value) {
+				$schema->addConstraint($name, $value);
+			}
 		}
+
 		return $this->_schema = $schema;
 	}
 
@@ -333,6 +346,10 @@ public function primaryKey($key = null) {
 		if ($key !== null) {
 			$this->_primaryKey = $key;
 		}
+		if ($this->_primaryKey === null) {
+			$key = current((array)$this->schema()->primaryKey());
+			$this->_primaryKey = $key ?: null;
+		}
 		return $this->_primaryKey;
 	}
 
@@ -1051,10 +1068,10 @@ protected function _insert($entity, $data) {
 
 		$success = false;
 		if ($statement->rowCount() > 0) {
-			if (!isset($data[$primary])) {
+			if ($primary && !isset($data[$primary])) {
 				$id = $statement->lastInsertId($this->table(), $primary);
 			}
-			if ($id !== null) {
+			if ($primary && $id !== null) {
 				$entity->set($primary, $id);
 			}
 			$success = $entity;
diff --git a/Cake/Test/TestCase/ORM/Association/BelongsToManyTest.php b/Cake/Test/TestCase/ORM/Association/BelongsToManyTest.php
index f725fc3ea57..e9e07b623da 100644
--- a/Cake/Test/TestCase/ORM/Association/BelongsToManyTest.php
+++ b/Cake/Test/TestCase/ORM/Association/BelongsToManyTest.php
@@ -43,6 +43,9 @@ public function setUp() {
 		$this->tag->schema([
 			'id' => ['type' => 'integer'],
 			'name' => ['type' => 'string'],
+			'_constraints' => [
+				'primary' => ['type' => 'primary', 'columns' => ['id']]
+			]
 		]);
 		$this->article = $this->getMock(
 			'Cake\ORM\Table', ['find', 'delete'], [['alias' => 'Articles', 'table' => 'articles']]
@@ -50,6 +53,9 @@ public function setUp() {
 		$this->article->schema([
 			'id' => ['type' => 'integer'],
 			'name' => ['type' => 'string'],
+			'_constraints' => [
+				'primary' => ['type' => 'primary', 'columns' => ['id']]
+			]
 		]);
 		TableRegistry::set('Articles', $this->article);
 	}
@@ -171,7 +177,10 @@ public function testAttachTo() {
 			'table' => 'articles_tags',
 			'schema' => [
 				'article_id' => ['type' => 'integer'],
-				'tag_id' => ['type' => 'integer']
+				'tag_id' => ['type' => 'integer'],
+				'_constraints' => [
+					'primary' => ['type' => 'primary', 'columns' => ['article_id', 'tag_id']]
+				]
 			]
 		]);
 		$association = new BelongsToMany('Tags', $config);
diff --git a/Cake/Test/TestCase/ORM/Association/BelongsToTest.php b/Cake/Test/TestCase/ORM/Association/BelongsToTest.php
index 7e8ab0a8528..6876915a323 100644
--- a/Cake/Test/TestCase/ORM/Association/BelongsToTest.php
+++ b/Cake/Test/TestCase/ORM/Association/BelongsToTest.php
@@ -40,6 +40,9 @@ public function setUp() {
 			'schema' => [
 				'id' => ['type' => 'integer'],
 				'company_name' => ['type' => 'string'],
+				'_constraints' => [
+					'primary' => ['type' => 'primary', 'columns' => ['id']]
+				]
 			]
 		]);
 		$this->client = TableRegistry::get('Clients', [
@@ -47,6 +50,9 @@ public function setUp() {
 				'id' => ['type' => 'integer'],
 				'client_name' => ['type' => 'string'],
 				'company_id' => ['type' => 'integer'],
+				'_constraints' => [
+					'primary' => ['type' => 'primary', 'columns' => ['id']]
+				]
 			]
 		]);
 	}
diff --git a/Cake/Test/TestCase/ORM/Association/HasManyTest.php b/Cake/Test/TestCase/ORM/Association/HasManyTest.php
index 2f090f18618..1d0811219d4 100644
--- a/Cake/Test/TestCase/ORM/Association/HasManyTest.php
+++ b/Cake/Test/TestCase/ORM/Association/HasManyTest.php
@@ -40,6 +40,9 @@ public function setUp() {
 			'schema' => [
 				'id' => ['type' => 'integer'],
 				'username' => ['type' => 'string'],
+				'_constraints' => [
+					'primary' => ['type' => 'primary', 'columns' => ['id']]
+				]
 			]
 		]);
 		$this->article = $this->getMock(
@@ -51,6 +54,9 @@ public function setUp() {
 			'id' => ['type' => 'integer'],
 			'title' => ['type' => 'string'],
 			'author_id' => ['type' => 'integer'],
+			'_constraints' => [
+				'primary' => ['type' => 'primary', 'columns' => ['id']]
+			]
 		]);
 	}
 
diff --git a/Cake/Test/TestCase/ORM/Association/HasOneTest.php b/Cake/Test/TestCase/ORM/Association/HasOneTest.php
index e229915f0bb..ccedab86aaf 100644
--- a/Cake/Test/TestCase/ORM/Association/HasOneTest.php
+++ b/Cake/Test/TestCase/ORM/Association/HasOneTest.php
@@ -39,6 +39,9 @@ public function setUp() {
 			'schema' => [
 				'id' => ['type' => 'integer'],
 				'username' => ['type' => 'string'],
+				'_constraints' => [
+					'primary' => ['type' => 'primary', 'columns' => ['id']]
+				]
 			]
 		]);
 		$this->profile = TableRegistry::get('Profiles', [
@@ -46,6 +49,9 @@ public function setUp() {
 				'id' => ['type' => 'integer'],
 				'first_name' => ['type' => 'string'],
 				'user_id' => ['type' => 'integer'],
+				'_constraints' => [
+					'primary' => ['type' => 'primary', 'columns' => ['id']]
+				]
 			]
 		]);
 	}
diff --git a/Cake/Test/TestCase/ORM/QueryTest.php b/Cake/Test/TestCase/ORM/QueryTest.php
index 5453369c065..d1c7f5c84d6 100644
--- a/Cake/Test/TestCase/ORM/QueryTest.php
+++ b/Cake/Test/TestCase/ORM/QueryTest.php
@@ -49,16 +49,27 @@ class QueryTest extends TestCase {
 	public function setUp() {
 		parent::setUp();
 		$this->connection = ConnectionManager::get('test');
-		$schema = ['id' => ['type' => 'integer']];
+		$schema = [
+			'id' => ['type' => 'integer'],
+			'_constraints' => [
+				'primary' => ['type' => 'primary', 'columns' => ['id']]
+			]
+		];
 		$schema1 = [
 			'id' => ['type' => 'integer'],
 			'name' => ['type' => 'string'],
-			'phone' => ['type' => 'string']
+			'phone' => ['type' => 'string'],
+			'_constraints' => [
+				'primary' => ['type' => 'primary', 'columns' => ['id']]
+			]
 		];
 		$schema2 = [
 			'id' => ['type' => 'integer'],
 			'total' => ['type' => 'string'],
-			'placed' => ['type' => 'datetime']
+			'placed' => ['type' => 'datetime'],
+			'_constraints' => [
+				'primary' => ['type' => 'primary', 'columns' => ['id']]
+			]
 		];
 
 		$this->table = $table = TableRegistry::get('foo', ['schema' => $schema]);
diff --git a/Cake/Test/TestCase/ORM/TableTest.php b/Cake/Test/TestCase/ORM/TableTest.php
index bea789fc34d..90a759f321d 100644
--- a/Cake/Test/TestCase/ORM/TableTest.php
+++ b/Cake/Test/TestCase/ORM/TableTest.php
@@ -128,7 +128,13 @@ public function testConnection() {
  * @return void
  */
 	public function testPrimaryKey() {
-		$table = new Table(['table' => 'users']);
+		$table = new Table([
+			'table' => 'users',
+			'schema' => [
+				'id' => ['type' => 'integer'],
+				'_constraints' => ['primary' => ['type' => 'primary', 'columns' => ['id']]]
+			]
+		]);
 		$this->assertEquals('id', $table->primaryKey());
 		$table->primaryKey('thingID');
 		$this->assertEquals('thingID', $table->primaryKey());
@@ -176,7 +182,8 @@ public function testDisplayFallback() {
 			'table' => 'users',
 			'schema' => [
 				'id' => ['type' => 'string'],
-				'foo' => ['type' => 'string']
+				'foo' => ['type' => 'string'],
+				'_constraints' => ['primary' => ['type' => 'primary', 'columns' => ['id']]]
 			]
 		]);
 		$this->assertEquals('id', $table->displayField());
@@ -192,7 +199,8 @@ public function testDisplaySet() {
 			'table' => 'users',
 			'schema' => [
 				'id' => ['type' => 'string'],
-				'foo' => ['type' => 'string']
+				'foo' => ['type' => 'string'],
+				'_constraints' => ['primary' => ['type' => 'primary', 'columns' => ['id']]]
 			]
 		]);
 		$this->assertEquals('id', $table->displayField());