问题
I am fairly new to Hibernate and need some help with hibernate-mapping.
I have 4 different classes which I want to map into one table, of which the primary key consists of attributes from 2 different classes. At the same time, I want to map only selected attributes from each class into a local database. I wish to avoid JPA annotations and define the mapping style in a hbm.xml file instead. How do I do that?
Take the following example:
public class Tenant implements Serializable {
private final static long serialVersionUID = 1L;
protected List<Rack> rack;
protected String type;
//getters setters
}
public class Rack implements Serializable {
private final static long serialVersionUID = 1L;
protected List<Circuit> circuit;
protected String rackLabel;
protected Boolean excludes;
//getters setters
}
public class Circuit implements Serializable {
private final static long serialVersionUID = 1L;
protected List<CircuitReadings> circuitReadings;
protected String circuitNo;
protected Boolean excludes;
//getters setters
}
public class CircuitReadings
implements Serializable {
private final static long serialVersionUID = 1L;
protected String date;
protected String kva;
protected String current;
protected String kwh;
//getters setters
}
And the eventual table should consist of the following:
type | rackLabel | circuitNo | date | kva | current | energy
"circuitNo" and "date" above should form the composite primary keys.
Can someone show me an example of how I should map this? Thanks!
回答1:
Hibernate provide a way to map subclass using discriminator keyword.
<class name="Payment" table="PAYMENT">
<id name="id" type="long" column="PAYMENT_ID">
<generator class="native"/>
</id>
<discriminator column="PAYMENT_TYPE" type="string"/>
<property name="amount" column="AMOUNT"/>
...
<subclass name="CreditCardPayment" discriminator-value="CREDIT">
<join table="CREDIT_PAYMENT">
<key column="PAYMENT_ID"/>
<property name="creditCardType" column="CCTYPE"/>
...
</join>
</subclass>
<subclass name="CashPayment" discriminator-value="CASH">
<join table="CASH_PAYMENT">
<key column="PAYMENT_ID"/>
...
</join>
</subclass>
<subclass name="ChequePayment" discriminator-value="CHEQUE">
<join table="CHEQUE_PAYMENT" fetch="select">
<key column="PAYMENT_ID"/>
...
</join>
</subclass>
</class>
回答2:
There's nothing stopping you from doing that . Create 4 HBMs pointing to the same table but different Pojos . Though it can be done , as @Ioan Alexandru Cucu , it is not recommended .
<!-- HBM1-->
<class name="com.myProject.Rack"
table="My_Table">
<!-- HBM2-->
<class name="com.myProject.Rack"
table="My_Table">
来源:https://stackoverflow.com/questions/8738761/hibernate-mapping-multiple-classes-to-one-table-using-hbm-xml