jpa多表查询可以使用构造器的方式进行多表查询，以下为多表查询的案例。
本案例中有A、B、C三个对象实体类，对象A、B通过属性imsi关联，对象B、C通过imsig关联；
还有一个Abc类，它是一个用来多表查询时构造集合的普通类。
以下为案例代码
A类
package com.ljq.entity;import java.io.Serializable;import javax.persistence.Column;import javax.persistence.Entity;import javax.persistence.GeneratedValue;import javax.persistence.Id;/** * 对象A、B通过属性imsi关联 * * @author jiqinlin * */@SuppressWarnings("serial")@Entitypublic class A implements Serializable { @Id @GeneratedValue private Integer id; @Column(nullable = false, length = 20) private String imsi; @Column(nullable = false, length = 20) private String sipss; public A() { super(); } public A(String imsi, String sipss) { super(); this.imsi = imsi; this.sipss = sipss; } public Integer getId() { return id; } public void setId(Integer id) { this.id = id; } public String getImsi() { return imsi; } public void setImsi(String imsi) { this.imsi = imsi; } public String getSipss() { return sipss; } public void setSipss(String sipss) { this.sipss = sipss; }}
B类
package com.ljq.entity;import java.io.Serializable;import javax.persistence.Column;import javax.persistence.Entity;import javax.persistence.GeneratedValue;import javax.persistence.Id;@SuppressWarnings("serial")@Entitypublic class B implements Serializable { @Id @GeneratedValue private Integer id; @Column(nullable = false, length = 20) private String imsi; @Column(nullable = false, length = 20) private String imsig; @Column(nullable = false, length = 20) private String mdn; public B() { super(); } public B(String imsi, String imsig, String mdn) { super(); this.imsi = imsi; this.imsig = imsig; this.mdn = mdn; } public Integer getId() { return id; } public void setId(Integer id) { this.id = id; } public String getImsi() { return imsi; } public void setImsi(String imsi) { this.imsi = imsi; } public String getImsig() { return imsig; } public void setImsig(String imsig) { this.imsig = imsig; } public String getMdn() { return mdn; } public void setMdn(String mdn) { this.mdn = mdn; }}
C类型
package com.ljq.entity;import java.io.Serializable;import javax.persistence.Column;import javax.persistence.Entity;import javax.persistence.GeneratedValue;import javax.persistence.Id;/** * 对象B、C通过属性imsig关联 * * @author jiqinlin * */@SuppressWarnings("serial")@Entitypublic class C implements Serializable { @Id @GeneratedValue private Integer id; @Column(nullable = false, length = 20) private String imsig; @Column(nullable = false, length = 20) private String ki; public C() { super(); } public C(String imsig, String ki) { super(); this.imsig = imsig; this.ki = ki; } public Integer getId() { return id; } public void setId(Integer id) { this.id = id; } public String getImsig() { return imsig; } public void setImsig(String imsig) { this.imsig = imsig; } public String getKi() { return ki; } public void setKi(String ki) { this.ki = ki; }}
Abc类型
package com.ljq.entity;import java.io.Serializable;/** * 多表查询时用来构造集合的实体类 * * @author jiqinlin * */@SuppressWarnings("serial")public class Abc implements Serializable { /** 实体类主键 * */ private Integer id; private String imsi; private String imsig; private String sipss; private String mdn; private String ki; public Abc() { } public Abc(String imsi, String sipss, String mdn) { this.imsi = imsi; this.sipss = sipss; this.mdn = mdn; } public Abc(String imsi, String imsig, String mdn, String ki) { super(); this.imsi = imsi; this.imsig = imsig; this.mdn = mdn; this.ki = ki; } public Abc(String imsi, String imsig, String sipss, String mdn, String ki) { super(); this.imsi = imsi; this.imsig = imsig; this.sipss = sipss; this.mdn = mdn; this.ki = ki; } public Integer getId() { return id; } public void setId(Integer id) { this.id = id; } public String getImsi() { return imsi; } public void setImsi(String imsi) { this.imsi = imsi; } public String getImsig() { return imsig; } public void setImsig(String imsig) { this.imsig = imsig; } public String getSipss() { return sipss; } public void setSipss(String sipss) { this.sipss = sipss; } public String getMdn() { return mdn; } public void setMdn(String mdn) { this.mdn = mdn; } public String getKi() { return ki; } public void setKi(String ki) { this.ki = ki; }}
MultiListQueryTest测试类
package junit.test;import java.util.List;import javax.persistence.EntityManager;import javax.persistence.EntityManagerFactory;import javax.persistence.Persistence;import org.junit.Test;import com.ljq.entity.A;import com.ljq.entity.Abc;import com.ljq.entity.B;import com.ljq.entity.C;/** * 多表查询 * * @author jiqinlin * */public class MultiListQueryTest { @Test public void add() throws Exception { EntityManagerFactory factory = Persistence.createEntityManagerFactory("ljq"); EntityManager em = factory.createEntityManager(); em.getTransaction().begin(); em.persist(new A("41650a", "abcefg1")); em.persist(new A("41650b", "abcefg2")); em.persist(new A("41650c", "abcefg3")); em.persist(new C("imsig_a","12345a")); em.persist(new C("imsig_b","12345b")); em.persist(new C("imsig_c","12345c")); em.persist(new C("imsig_e","12345d")); em.persist(new B("41650a", "imsig_a", "059188893381")); em.persist(new B("41650b", "imsig_b", "059188893382")); em.persist(new B("41650e", "imsig_c", "059188893383")); em.persist(new B("41650aa", "imsig_123", "059188893384")); em.persist(new B("41650cc", "imsig_1", "059188893385")); em.getTransaction().commit(); em.close(); factory.close(); } /** * 多表查询对象A、B * * @throws Exception */ @Test public void queryAB() throws Exception { EntityManagerFactory factory = Persistence.createEntityManagerFactory("ljq"); EntityManager em = factory.createEntityManager(); List<Abc> abcs = em.createQuery("select new com.ljq.entity.Abc(a.imsi, a.sipss, b.mdn) " + "from A a, B b where a.imsi=b.imsi").getResultList(); for(Abc abc : abcs){ System.out.println("imsi:"+abc.getImsi()); System.out.println("sipss:"+abc.getSipss()); System.out.println("mdn:"+abc.getMdn()); System.out.println("========"); } em.close(); factory.close(); } /** * 多表查询对象B、C * * @throws Exception */ @Test public void queryBC() throws Exception { EntityManagerFactory factory = Persistence.createEntityManagerFactory("ljq"); EntityManager em = factory.createEntityManager(); List<Abc> abcs = em.createQuery("select new com.ljq.entity.Abc(b.imsi, b.imsig, b.mdn, c.ki) " + "from B b, C c where b.imsig=c.imsig").getResultList(); for(Abc abc : abcs){ System.out.println("imsi:"+abc.getImsi()); System.out.println("imsig:"+abc.getImsig()); System.out.println("mdn:"+abc.getMdn()); System.out.println("ki:"+abc.getKi()); System.out.println("======="); } em.close(); factory.close(); } /** * 多表查询对象A、B、C * * @throws Exception */ @Test public void queryABC() throws Exception { EntityManagerFactory factory = Persistence.createEntityManagerFactory("ljq"); EntityManager em = factory.createEntityManager(); List<Abc> abcs = em.createQuery("select new com.ljq.entity.Abc(b.imsi, b.imsig, a.sipss, b.mdn, c.ki) " + "from A a, B b, C c where a.imsi=b.imsi and b.imsig=c.imsig").getResultList(); for(Abc abc : abcs){ System.out.println("imsi:"+abc.getImsi()); System.out.println("imsig:"+abc.getImsig()); System.out.println("sipss:"+abc.getSipss()); System.out.println("mdn:"+abc.getMdn()); System.out.println("ki:"+abc.getKi()); System.out.println("======="); } em.close(); factory.close(); } @Test public void test() throws Exception { Persistence.createEntityManagerFactory("ljq"); } }
来源：http://www.cnblogs.com/linjiqin/archive/2011/02/11/1951375.html