Components as composite identifiers in Hibernate

问题:

I am following Hibernate Documentation and trying to implement the example given for section 9.4. Components as composite identifiers but facing issues on how to implement it.

Here is what I have done:

My entity classes:

Order.java

public class Order {
    private int id;
    private Set<OrderLine> lines = new HashSet<OrderLine>();
   // Setters & Getters
}

OrderLine.java

public class OrderLine {
    private OrderLineId id;
    private String name;
    private Order order;
   // Setters & Getters
}

OrderLineId.java

public class OrderLineId implements Serializable{
    private int lineId;
    private int orderId;
    private int customerId;
   // Setters & Getters
}

My mapping file which is having issues:

<hibernate-mapping>
   <class name="Order" table="TEST_Order">
      <id name="id" type="int" column="id">
         <generator class="native"/>
      </id>
      <set name="lines" cascade="all">
         <key column="orderId"/>
         <one-to-many class="OrderLine"/>
      </set>
   </class>

<class name="OrderLine" table="TEST_OrderLine">
    <composite-id name="id" class="OrderLineId">
        <key-property name="lineId"/>
        <key-property name="orderId"/>
        <key-property name="customerId"/>
    </composite-id>

    <property name="name"/>

    <many-to-one name="order" class="Order"
            insert="false" update="false">
        <column name="orderId"/>
        <column name="customerId"/>
    </many-to-one>
</class>
</hibernate-mapping>

When I am trying to create a session factory which parses this mapping file, I am getting an exception saying:

Caused by: org.hibernate.MappingException: Foreign key (FK_89b4nqt5l2n6tfd1d5tq0ill0:TEST_OrderLine [orderId,customerId])) must have same number of columns as the referenced primary key (TEST_Order [id])
    at org.hibernate.mapping.ForeignKey.alignColumns(ForeignKey.java:110)
    at org.hibernate.mapping.ForeignKey.alignColumns(ForeignKey.java:93)
    at org.hibernate.cfg.Configuration.secondPassCompileForeignKeys(Configuration.java:1816)
    at org.hibernate.cfg.Configuration.originalSecondPassCompile(Configuration.java:1739)
    at org.hibernate.cfg.Configuration.secondPassCompile(Configuration.java:1424)
    at org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:1844)

Can someone please help me how to implement the example given in the documentation.

回答1:

The OrderLine needs to refernece the Order PK, which is not a composite key.

It means the many-to-one must be:

<many-to-one name="order" class="Order"
        insert="false" update="false">
    <column name="orderId"/>
</many-to-one>

The orderId is the FK to Order.id.

Then the one-to-many side will become:

<set name="lines" cascade="all">
    <key>
        <column name="orderId"/>
    </key>
    <one-to-many class="OrderLine"/>
</set>

So even if the OrderLine has a composite-key, the reference is made after Order.id, which is a simple key.

If you want to map other association to OrderLine, like OrderLineProduct then you'll need to use the composite-key to map the association between the parent (OrderLine) and the child (OrderLineProduct), so that OrderLineProduct has a composite-foreign-key back to OrderLine.

回答2:

In both the table hbm mapping you should have same no. of column ,what you are using to make composite.You need to add these 3 column in TEST_Oder.
Example to follow :

<many-to-one name="orderLine" class="OrderLine">
<column name="lineId"/>
<column name="orderId"/>
<column name="customerId"/>
</many-to-one>

Refer same URL