Symfony2 级联删除

我有两个实体：

1. 仓库

     id | name           
     ---------------------
     1  | Warehouse 1
     2  | Warehouse 2
   

2. 项目

     id | warehouse_id   | name
     --------------------------------------
     1  | 1              |  Item 1
     2  | 2              |  Item 2
   

我想知道如何从仓库表中删除"仓库 1"warehouse_id的值为 Null。实际上，如果我删除"仓库 1"warehouse_id我需要在数据库中的所有表上设置为 NULL。

例如，在我的"项目"实体中，我设置了此设置，当我删除"仓库 1"时，它似乎对我没有任何作用

 /**
 * @ORM'ManyToOne(targetEntity="WIC'WarehouseBundle'Entity'Warehouse", inversedBy="purchaseOrderLineItemLocation")
 * @ORM'JoinColumn(name="warehouse_id", referencedColumnName="id", nullable=true, onDelete="SET NULL")
 * @Common'Versioned
 */
protected $warehouse;

这是我的完整仓库实体

这里有什么需要设置的吗？

 /**
 * @var integer
 *
 * @ORM'Column(name="id", type="integer")
 * @ORM'Id
 * @ORM'GeneratedValue(strategy="AUTO")
 */
private $id;
/**
 * @var string
 * @ORM'Column(name="name", type="string", length=255)
 * @Common'Versioned
 * @Assert'NotBlank(message="Location Name cannot be blank.")
 */
private $name;
/**
 * @var string $description
 *
 * @Common'Versioned
 * @ORM'Column(name="description", type="text")
 */
protected $description;
/**
 * @var string
 * @ORM'Column(name="address", type="string", length=255)
 * @Common'Versioned
 * @Assert'NotBlank(message="Address cannot be blank.")
 */
private $address;
/**
 * @var string
 * @ORM'Column(name="address2", type="string", length=255, nullable=true)
 * @Common'Versioned
 */
private $address2;
/**
 * @var string
 * @ORM'Column(name="city", type="string", length=255)
 * @Common'Versioned
 * @Assert'NotBlank(message="City cannot be blank.")
 */
private $city;
/**
 * @var string
 * @ORM'Column(name="state", type="string", length=255)
 * @Common'Versioned
 * @Assert'NotBlank(message="State cannot be blank.")
 */
private $state;
/**
 * @var string
 * @ORM'Column(name="zip", type="string", length=255)
 * @Gedmo'Versioned
 * @Assert'NotBlank(message="Zip cannot be blank.")
 */
private $zip;
/**
 * @var string
 * @ORM'Column(name="country", type="string", length=255, nullable=true)
 * @Common'Versioned
 */
private $country;
/**
 * @var string
 * @ORM'Column(name="phone", type="string", length=255, nullable=true)
 * @Common'Versioned
 */
private $phone;
/**
 * @var string
 * @ORM'Column(name="email", type="string", length=255, nullable=true)
 * @Common'Versioned
 */
private $email;
/**
 * @var string
 * @ORM'Column(name="fax", type="string", length=255, nullable=true)
 * @Common'Versioned
 */
private $fax;
/**
 * @ORM'OneToMany(targetEntity="WIC'InventoryLocationBundle'Entity'InventoryLocation", mappedBy="inventoryLocation")
 */
protected $inventoryLocations;
/**
 * @ORM'ManyToOne(targetEntity="WIC'UserBundle'Entity'User")
 * @ORM'JoinColumn(name="created_by", referencedColumnName="id")
 * @Common'Blameable(on="create")
 */
private $createdBy;
/**
 * @ORM'ManyToOne(targetEntity="WIC'UserBundle'Entity'User")
 * @ORM'JoinColumn(name="updated_by", referencedColumnName="id")
 * @Common'Blameable(on="update")
 */
private $updatedBy;
/**
 * @ORM'ManyToOne(targetEntity="WIC'AccountBundle'Entity'Account", inversedBy="warehouses")
 * @ORM'JoinColumn(name="account_id", referencedColumnName="id", nullable=false)
 * @Common'Versioned
 * @Common'Blameable(on="create")
*/
protected $account;
/**
 * @var datetime $created
 *
 * @Common'Timestampable(on="create")
 * @ORM'Column(type="datetime")
 */
private $created;
/**
 * @var datetime $updated
 *
 * @Common'Timestampable(on="update")
 * @ORM'Column(type="datetime", nullable=true)
 */
private $updated;
/**
 * @ORM'Column(name="deletedAt", type="datetime", nullable=true)
 */
private $deletedAt;

public function __construct()
{
    $this->inventoryLocations = new ArrayCollection();
}