hibernate 联合主键 composite-id

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本文深入探讨了在Hibernate框架中使用复合标识符的三种方法：嵌入式组合标识符、映射式组合标识符和标识符组件，并详细解释了每种方法的优缺点及如何在实际应用中实现。

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<composite-id
        name="propertyName"
        class="ClassName"
        mapped="true|false"
        access="field|property|ClassName"
        node="element-name|."
        >

        <key-property name="propertyName" type="typename" column="column_name"/>
        <key-many-to-one name="propertyName class="ClassName" column="column_name"/>
        ......
</composite-id>

如果表使用联合主键，你可以映射类的多个属性为标识符属性。 <composite-id>元素接受<key-property> 属性映射和<key-many-to-one>属性映射作为子元素。

<composite-id>
        <key-property name="medicareNumber"/>
        <key-property name="dependent"/>
</composite-id>

你的持久化类必须重载equals()和hashCode()方法，来实现组合的标识符的相等判断。实现Serializable接口也是必须的。

不幸的是，这种组合关键字的方法意味着一个持久化类是它自己的标识。除了对象自己之外，没有什么方便的“把手”可用。你必须初始化持久化类的实例，填充它的标识符属性，再load() 组合关键字关联的持久状态。我们把这种方法称为embedded（嵌入式）的组合标识符，在重要的应用中不鼓励使用这种用法。

第二种方法我们称为mapped(映射式)组合标识符 (mapped composite identifier),<composite-id>元素中列出的标识属性不但在持久化类出现，还形成一个独立的标识符类。

<composite-id class="MedicareId" mapped="true">
        <key-property name="medicareNumber"/>
        <key-property name="dependent"/>
</composite-id>

在这个例子中，组合标识符类MedicareId和实体类都含有medicareNumber和dependent属性。标识符类必须重载equals()和hashCode()并且实现Serializable接口。这种方法的缺点是出现了明显的代码重复。

下面列出的属性是用来指定一个映射式组合标识符的：

mapped (可选, 默认为false): 指明使用一个映射式组合标识符，其包含的属性映射同时在实体类和组合标识符类中出现。
class (可选,但对映射式组合标识符必须指定): 作为组合标识符类使用的类名.

name (可选,但对这种方法而言必须): 包含此组件标识符的组件类型的名字.
access (可选 - 默认为property): Hibernate应该使用的访问此属性值的策略
class (可选 - 默认会用反射来自动判定属性类型 ): 用来作为组合标识符的组件类的类名

第三种方式，被称为identifier component(标识符组件)是我们对几乎所有应用都推荐使用的方式。

例子:

POJO

package com.pojo.basic;

// Generated 2011-11-18 10:24:33 by Hibernate Tools 3.4.0.CR1

import java.math.BigDecimal;

/**
 * CurId 幣別
 */
public class CurId implements java.io.Serializable {

	private static final long serialVersionUID = 1L;
	private CurIdId id;    //此处为联合主键
	private String name;
	private BigDecimal excRto;
	private String accNoIr;
	private String accNoIp;
	private String accNoChk;
	private BigDecimal excRtoE;
	private BigDecimal excRtoI;
	private BigDecimal excRtoO;
	private String idSgt;
	private byte[] upDd;

	public CurId() {
	}

	public CurId(CurIdId id) {
		this.id = id;
	}

	public CurId(CurIdId id, String name, BigDecimal excRto, String accNoIr,
			String accNoIp, String accNoChk, BigDecimal excRtoE,
			BigDecimal excRtoI, BigDecimal excRtoO, String idSgt, byte[] upDd) {
		this.id = id;
		this.name = name;
		this.excRto = excRto;
		this.accNoIr = accNoIr;
		this.accNoIp = accNoIp;
		this.accNoChk = accNoChk;
		this.excRtoE = excRtoE;
		this.excRtoI = excRtoI;
		this.excRtoO = excRtoO;
		this.idSgt = idSgt;
		this.upDd = upDd;
	}

	public CurIdId getId() {
		return this.id;
	}

	public void setId(CurIdId id) {
		this.id = id;
	}

	public String getName() {
		return this.name;
	}

	public void setName(String name) {
		this.name = name;
	}

	public BigDecimal getExcRto() {
		return this.excRto;
	}

	public void setExcRto(BigDecimal excRto) {
		this.excRto = excRto;
	}

	public String getAccNoIr() {
		return this.accNoIr;
	}

	public void setAccNoIr(String accNoIr) {
		this.accNoIr = accNoIr;
	}

	public String getAccNoIp() {
		return this.accNoIp;
	}

	public void setAccNoIp(String accNoIp) {
		this.accNoIp = accNoIp;
	}

	public String getAccNoChk() {
		return this.accNoChk;
	}

	public void setAccNoChk(String accNoChk) {
		this.accNoChk = accNoChk;
	}

	public BigDecimal getExcRtoE() {
		return this.excRtoE;
	}

	public void setExcRtoE(BigDecimal excRtoE) {
		this.excRtoE = excRtoE;
	}

	public BigDecimal getExcRtoI() {
		return this.excRtoI;
	}

	public void setExcRtoI(BigDecimal excRtoI) {
		this.excRtoI = excRtoI;
	}

	public BigDecimal getExcRtoO() {
		return this.excRtoO;
	}

	public void setExcRtoO(BigDecimal excRtoO) {
		this.excRtoO = excRtoO;
	}

	public String getIdSgt() {
		return this.idSgt;
	}

	public void setIdSgt(String idSgt) {
		this.idSgt = idSgt;
	}

	public byte[] getUpDd() {
		return this.upDd;
	}

	public void setUpDd(byte[] upDd) {
		this.upDd = upDd;
	}

}

//联合主键bean

package com.pojo.basic;

// Generated 2011-11-18 10:24:33 by Hibernate Tools 3.4.0.CR1

import java.util.Date;

/**
 * CurIdId generated by hbm2java
 */
public class CurIdId implements java.io.Serializable {

	private static final long serialVersionUID = 1L;
	private String curId;
	private Date ijDd;

	public CurIdId() {
	}

	public CurIdId(String curId, Date ijDd) {
		this.curId = curId;
		this.ijDd = ijDd;
	}

	public String getCurId() {
		return this.curId;
	}

	public void setCurId(String curId) {
		this.curId = curId;
	}

	public Date getIjDd() {
		return this.ijDd;
	}

	public void setIjDd(Date ijDd) {
		this.ijDd = ijDd;
	}
        //重写equals 和hashcode方法
	public boolean equals(Object other) {
		if ((this == other))
			return true;
		if ((other == null))
			return false;
		if (!(other instanceof CurIdId))
			return false;
		CurIdId castOther = (CurIdId) other;

		return ((this.getCurId() == castOther.getCurId()) || (this.getCurId() != null
				&& castOther.getCurId() != null && this.getCurId().equals(
				castOther.getCurId())))
				&& ((this.getIjDd() == castOther.getIjDd()) || (this.getIjDd() != null
						&& castOther.getIjDd() != null && this.getIjDd()
						.equals(castOther.getIjDd())));
	}

	public int hashCode() {
		int result = 17;

		result = 37 * result
				+ (getCurId() == null ? 0 : this.getCurId().hashCode());
		result = 37 * result
				+ (getIjDd() == null ? 0 : this.getIjDd().hashCode());
		return result;
	}

配置映射文件 hbm.xml

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<!-- Generated 2011-11-18 10:24:34 by Hibernate Tools 3.4.0.CR1 -->
<hibernate-mapping>
    <class name="com.pojo.basic.CurId" table="CUR_ID" schema="dbo" catalog="DB_GTC">
        <composite-id name="id" class="com.pojo.basic.CurIdId">
            <key-property name="curId" type="string">
                <column name="CUR_ID" length="4" />
            </key-property>
            <key-property name="ijDd" type="timestamp">
                <column name="IJ_DD" length="23" />
            </key-property>
        </composite-id>
        <property name="name" type="string">
            <column name="NAME" length="20" />
        </property>
        <property name="excRto" type="big_decimal">
            <column name="EXC_RTO" precision="28" scale="8" />
        </property>
        <property name="accNoIr" type="string">
            <column name="ACC_NO_IR" length="20" />
        </property>
        <property name="accNoIp" type="string">
            <column name="ACC_NO_IP" length="20" />
        </property>
        <property name="accNoChk" type="string">
            <column name="ACC_NO_CHK" length="20" />
        </property>
        <property name="excRtoE" type="big_decimal">
            <column name="EXC_RTO_E" precision="28" scale="8" />
        </property>
        <property name="excRtoI" type="big_decimal">
            <column name="EXC_RTO_I" precision="28" scale="8" />
        </property>
        <property name="excRtoO" type="big_decimal">
            <column name="EXC_RTO_O" precision="28" scale="8" />
        </property>
        <property name="idSgt" type="string">
            <column name="ID_SGT" length="10" />
        </property>
        <property name="upDd" type="binary">
            <column name="UP_DD" />
        </property>
    </class>
</hibernate-mapping>