三、使用T/CCU(Table Per Concrete Class with Union)策略來映射 ?

1. 只對Concrete Class建立Table，SuperClass中的property，直接mapping到Concrete Class相應Table的column

2. 對于Concrete Class的mapping，使用union-subclass的方式來Mapping。

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Mapping File如下：

    <?xml version="1.0" encoding="UTF-8"?>

<!DOCTYPE hibernate-mapping PUBLIC
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN" 
    "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping>
        <class name="org.example.hibernate.domain.BillingDetail"
	       abstract="true"> <!-- 必須聲明abstract="true"-->
            <id name="id" column="IDNUM" type="long">
                <generator class="hilo"/>
            </id>

            <property name="owner" type="string" column="OWNER" length="30" />

            <union-subclass name="org.example.hibernate.domain.CreditCard" 
	                    table="CREDIT_CARD">
                <property name="number" type="string" column="NUMBER_CODE" length="20" />
                <property name="expMonth" type="string" column="EXP_MONTH" length="2" />
                <property name="expYear" type="string" column="EXP_YEAR" length="4" />
            </union-subclass>

            <union-subclass name="org.example.hibernate.domain.BankAccount" 
	                    table="BANK_ACCOUNT">
                <property name="account" type="string" column="ACCOUNT" length="20" />
                <property name="bankName" type="string" column="BANK_NAME" length="255" />
                <property name="swift" type="string" column="SWIFT" length="3" />
            </union-subclass>
        </class>
</hibernate-mapping>
  

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1.當對Concrete Class做save的時候，會首先generate id，以確保該id為2張table的唯一。

    CreditCard cc21 = new CreditCard();
cc21.setOwner("jessecia");
cc21.setNumber("123123123123123");
		
session.save(cc21);
  

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?? 相應的SQL

    select max(ids_.IDNUM) from ( select IDNUM from CREDIT_CARD union select IDNUM from BANK_ACCOUNT ) ids_

insert into CREDIT_CARD (OWNER, NUMBER_CODE, EXP_MONTH, EXP_YEAR, IDNUM) values (?, ?, ?, ?, ?)
  

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2.對于BillDetail的Query轉為union方式獲得。??

    List list = session.createQuery("from BillingDetail2 bd1 where bd1.owner = :owner")
                   .setParameter("owner", "jessecia")
		           .list();
		
  

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???相應SQL如下：

    select billingdet0_.IDNUM as IDNUM0_
     , billingdet0_.OWNER as OWNER0_
     , billingdet0_.NUMBER_CODE as NUMBER1_1_
     , billingdet0_.EXP_MONTH as EXP2_1_
     , billingdet0_.EXP_YEAR as EXP3_1_
     , billingdet0_.ACCOUNT as ACCOUNT2_
     , billingdet0_.BANK_NAME as BANK2_2_
     , billingdet0_.SWIFT as SWIFT2_
     , billingdet0_.clazz_ as clazz_ 
from ( 
      select IDNUM
           , null as SWIFT
	       , EXP_YEAR
	       , null as ACCOUNT
	       , OWNER
	       , EXP_MONTH
	       , NUMBER_CODE
	       , null as BANK_NAME
	       , 1 as clazz_ 
       from CREDIT_CARD 
       
       union 
       
      select IDNUM
           , SWIFT
	       , null as EXP_YEAR
	       , ACCOUNT
	       , OWNER
	       , null as EXP_MONTH
	       , null as NUMBER_CODE
	       , BANK_NAME
	       , 2 as clazz_ 
       from BANK_ACCOUNT 
      ) billingdet0_
where billingdet0_.OWNER=?
  

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?上一篇：Class Hierachy的映射策略之T/CCIP

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Class Hierachy的映射策略之T/CCU