Cascade delete and one-to-one mapping in hibernate

Question

In a web application which creates Bill for SaleOrder for a Buyer, I tried to create database tables and hibernate mappings. The relationships between the entities are:

1. A Bill has a Buyer and a SaleOrder

2. A SaleOrder has a Buyer.

3. When a SaleOrder is deleted, the associated Bill must be deleted.

I Implemented the java classes,created tables.

In the schema, table SALEORDER has a FK column 'BUYER_ID'. This table has no other foreign key columns. The table BILL has two foreign keys, BUYER_ID and SALEORDER_ID.

How do I map Bill and SaleOrder using one-to-one relation AND make sure that when a SaleOrder is deleted, the Bill is also deleted?

I am confused because, since the SaleOrder table has no foreign key named INVOICE_ID, how can I map the following in SaleOrder.hbm.xml?

<!-- 1-to-1 modelled using n-to-n + unique  -->
    <many-to-one name="invoice" class="Invoice" column="INVOICE_ID" cascade="delete" unique="true">
    </many-to-one>

If I put the mapping only in Bill.hbm.xml,will I be able to mention cascade delete (which should delete Bill when SaleOrder is deleted)?

Hope someone can suggest a solution.

---

The classes in my application are:

class Buyer{
   private Long buyerId;
   private String name;
...
}

class SaleOrder{
    private Long saleOrderId;
    ...
    private Buyer buyer;
...
}

class Bill{
   private Long billId;
   ...
   private Buyer buyer;
   private SaleOrder saleOrder;
...
}

The schema is:

CREATE TABLE BUYER(
   BUYER_ID BIGINT NOT NULL PRIMARY KEY IDENTITY,
   NAME VARCHAR(100)
);

CREATE TABLE SALEORDER(
   SALEORDER_ID BIGINT NOT NULL PRIMARY KEY IDENTITY,
   BUYER_ID BIGINT NOT NULL,
);

CREATE TABLE BILL(
  BILL_ID BIGINT NOT NULL PRIMARY KEY IDENTITY,
  BUYER_ID BIGINT NOT NULL,
  SALEORDER_ID BIGINT NOT NULL,
);
ALTER TABLE SALEORDER ADD CONSTRAINT FK_SO_BUYER FOREIGN KEY(BUYER_ID) REFERENCES BUYER(BUYER_ID);
ALTER TABLE BILL ADD CONSTRAINT FK_BILL_BUYER FOREIGN KEY(BUYER_ID) REFERENCES BUYER(BUYER_ID);
ALTER TABLE BILL ADD CONSTRAINT FK_BILL_SO FOREIGN KEY(SALEORDER_ID) REFERENCES SALEORDER(SALEORDER_ID);

Answer 1

Let me answer your questions using annotations, the XML configuration seems a little old-fashioned to me. The solution is to hold no references in Bill. But SaleOrder will hold a 1-1 reference to Bill and Buyer a 1-n reference to SaleOrder, using CascadeType.DELETE_ORPHAN above the relationship definitions. Thus, when a SaleOrder is deleted, the underlying Bill is deleted, and when a Buyer is deleted the underlying SaleOrder's and them underlying Bill's are deleted.

class Bill{
    private Long billId;    
    ...    
}

class SaleOrder{    
    private Long saleOrderId;     
    ...     
    @OneToOne(cascade=CascadeType.ALL, fetch=FetchType.LAZY)
    @Cascade( {org.hibernate.annotations.CascadeType.DELETE_ORPHAN} )
    private Bill bill; 
    ... 
}

class Buyer {
    private Long buyerId;
    private String name;
    ...     
    @OneToMany(cascade=CascadeType.ALL, fetch=FetchType.LAZY)
    @Cascade( {org.hibernate.annotations.CascadeType.DELETE_ORPHAN} )
    private List<SaleOrder> saleOrders; 
    ... 
}   

You must code your DAOs to get the Buyer for a SaleOrder and the SaleOrder for a bill. This is of course, another question, how to do this. But you should find good books and web resources on it.