由于OnDelete注释。

OnDelete注释仅在Hibernate生成架构时使用。它在数据库中配置外键，以便删除被引用的行时，包含外键的行也被删除。

请参阅

但是当你删除产品时，Hibernate也会删除供应商（这可能不是你想要的） ，因为在关联上设置了CascadeType.ALL。您应该删除该属性：当其中一个产品被移除时，没有理由删除供应商。

I am using spring, JPA with Hibernate.

I got the following entities:

@Entity
@Table(name = "Supplier")
public class Supplier {

   @Id
   @Column(name = "Supplier_ID", nullable = false)
   private Integer supplierId;

   ...
}

and,

@Entity
@Table(name = "Product")
public class Product {

   @Id
   private Integer productId;

   @ManyToOne(cascade = CascadeType.ALL)
   @OnDelete(action = OnDeleteAction.CASCADE)
   @JoinColumn(name = "Supplier_ID")
   private Supplier supplier;

   ...
}

Now, my question is, with the given schema

1. when I delete a row from child ( ie. Product), will the Supplier will also get deleted?
2. Or, it is only when the Parent (ie. Supplier) get deleted then it is cascaded to delete all the child 'Products'

Thanks.

The product will be removed when the supplier is removed due to the OnDelete annotation.

The OnDelete annotation is used only when the schema is generated by Hibernate. It configures the foreign key in database so that when the referenced row is deleted, the row containing the foreign key is also deleted.

See http://docs.jboss.org/hibernate/annotations/3.5/reference/en/html_single/#entity-hibspec-singleassoc

But Hibernate will also delete the supplier when you delete the product (which is probably not what you want), because of the CascadeType.ALL set on the association. You should remove this attribute: there is no reason to delete a supplier when one of its product is removed.