首先在开发之中复合主键是一中强烈不建议使用的技术，在任何一张数据表里面如果要设置主键应该只设置一个字段，但是复合主键毕竟属于标准的SQL语法，所以在Hibernate或者是JPA之中也都有复合主键的定义支持。
范例：数据库脚本

-- 删除数据表 DROP TABLE IF EXISTS member; -- 创建数据表 CREATE TABLE member( 	mid VARCHAR(50), 	mname VARCHAR(50), 	mage INT, 	CONSTRAINT pk_mid_name PRIMARY KEY(mid,name) ); 

此时设置了两个主键，但是一定要记住一点，主键不应该重复，所以在随后生成Hibernate操作的时候就要观察它生成类的形式。

1 基于HBM文件的配置

范例：定义MemberId类

@SuppressWarnings("serial") public class MemberId implements java.io.Serializable {  	// Fields  	private String mid; 	private String mname; } 

为了能够确定唯一，在这个MemberId类里面必须要覆写equals()和hashCode()两个方法。
范例：在Member类里面利用MemberId来描述复合主键

@SuppressWarnings("serial") public class Member implements java.io.Serializable {  	// Fields  	private MemberId id; 	private Integer mage; } 

随后需要观察Member.hbm.xml文件的组成。

<?xml version="1.0" encoding="utf-8"?> <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "https://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd"> <!--      Mapping file autogenerated by MyEclipse Persistence Tools --> <hibernate-mapping>     <class name="org.lks.pojo.Member" table="member" catalog="hedb">     	<!-- 取代的是id元素，表示此时的id是一个复合主键 -->         <composite-id name="id" class="org.lks.pojo.MemberId">             <key-property name="mid" type="java.lang.String">                 <column name="mid" length="50" />             </key-property>             <key-property name="mname" type="java.lang.String">                 <column name="mname" length="50" />             </key-property>         </composite-id>         <property name="mage" type="java.lang.Integer">             <column name="mage" />         </property>     </class> </hibernate-mapping>  

范例：测试代码

package org.lks.test;  import org.lks.dbc.HibernateSessionFactory; import org.lks.pojo.Member; import org.lks.pojo.MemberId;  public class TestMemberInsert {  	public static void main(String[] args) { 		MemberId id = new MemberId(); 		id.setMid("3161301220"); 		id.setMname("lks"); 		Member vo = new Member(); 		vo.setId(id); 		vo.setMage(23); 		HibernateSessionFactory.getSession().save(vo); 		HibernateSessionFactory.getSession().beginTransaction().commit(); 		HibernateSessionFactory.closeSession(); 		System.exit(0); 	} }  

Hibernate:      insert      into         hedb.member         (mage, mid, mname)      values         (?, ?, ?) 

此时信息可以正常保存（复合主键不重复）。

当然在进行数据查询的时候也有一些需要注意的概念，既然ID不能够重复，所以在数据查询中使用的get()方法来讲就必须考虑到复合主键不能重复的特点，所以才覆写了hashCode()以及equals()方法。
范例：数据查询

package org.lks.test;  import org.lks.dbc.HibernateSessionFactory; import org.lks.pojo.Member; import org.lks.pojo.MemberId;  public class TestMemberGet {  	public static void main(String[] args) { 		MemberId id = new MemberId(); 		id.setMid("3161301220"); 		id.setMname("lks"); 		Member vo = (Member)HibernateSessionFactory.getSession().get(Member.class, id); 		System.out.println(vo); 		HibernateSessionFactory.closeSession(); 		System.exit(0); 	} }  

Hibernate:      select         member0_.mid as mid1_0_0_,         member0_.mname as mname2_0_0_,         member0_.mage as mage3_0_0_      from         hedb.member member0_      where         member0_.mid=?          and member0_.mname=? org.lks.pojo.Member@3d7fa3ae 

所有的类的属性都会自动的根据配置进行不同类型的关系组成。

2 Annotation配置

虽然复合主键出现较少，但是在JPA的开发标准中依然支持了复合主键映射，并且这个复合主键的映射与之前的细粒度划分不同，它可以完美的配置。
范例：观察生成的MemberId程序类

package org.lks.pojo;  import javax.persistence.Column; import javax.persistence.Embeddable;  /**  * MemberId entity. @author MyEclipse Persistence Tools  */ @SuppressWarnings("serial") @Embeddable  public class MemberId implements java.io.Serializable {  	// Fields  	private String mid; 	private String mname;  	// Constructors  	/** default constructor */ 	public MemberId() { 	}  	/** full constructor */ 	public MemberId(String mid, String mname) { 		this.mid = mid; 		this.mname = mname; 	}  	// Property accessors  	@Column(name = "mid", nullable = false, length = 50)  	public String getMid() { 		return this.mid; 	}  	public void setMid(String mid) { 		this.mid = mid; 	}  	@Column(name = "mname", nullable = false, length = 50)  	public String getMname() { 		return this.mname; 	}  	public void setMname(String mname) { 		this.mname = mname; 	}  	public boolean equals(Object other) { 		if ((this == other)) 			return true; 		if ((other == null)) 			return false; 		if (!(other instanceof MemberId)) 			return false; 		MemberId castOther = (MemberId) other;  		return ((this.getMid() == castOther.getMid()) 				|| (this.getMid() != null && castOther.getMid() != null && this.getMid().equals(castOther.getMid()))) 				&& ((this.getMname() == castOther.getMname()) || (this.getMname() != null 						&& castOther.getMname() != null && this.getMname().equals(castOther.getMname()))); 	}  	public int hashCode() { 		int result = 17;  		result = 37 * result + (getMid() == null ? 0 : this.getMid().hashCode()); 		result = 37 * result + (getMname() == null ? 0 : this.getMname().hashCode()); 		return result; 	}  } 

范例：观察Member.java类

package org.lks.pojo;  import javax.persistence.AttributeOverride; import javax.persistence.AttributeOverrides; import javax.persistence.Column; import javax.persistence.EmbeddedId; import javax.persistence.Entity; import javax.persistence.Table;  /**  * Member entity. @author MyEclipse Persistence Tools  */ @SuppressWarnings("serial") @Entity @Table(name = "member", catalog = "hedb")  public class Member implements java.io.Serializable {  	// Fields  	private MemberId id; 	private Integer mage;  	// Constructors  	/** default constructor */ 	public Member() { 	}  	/** minimal constructor */ 	public Member(MemberId id) { 		this.id = id; 	}  	/** full constructor */ 	public Member(MemberId id, Integer mage) { 		this.id = id; 		this.mage = mage; 	}  	// Property accessors 	@EmbeddedId  	@AttributeOverrides({ 			@AttributeOverride(name = "mid", column = @Column(name = "mid", nullable = false, length = 50)), 			@AttributeOverride(name = "mname", column = @Column(name = "mname", nullable = false, length = 50)) })  	public MemberId getId() { 		return this.id; 	}  	public void setId(MemberId id) { 		this.id = id; 	}  	@Column(name = "mage")  	public Integer getMage() { 		return this.mage; 	}  	public void setMage(Integer mage) { 		this.mage = mage; 	}  } 

由于有开发工具的支持，使用复合主键比较方便。

数据库技术:10 15 Hibernate之复合主键映射地址：https://blog.csdn.net/weixin_43762330/article/details/107139357

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