Java持久性API（JPA）第6讲——关系操作

目标：通过实例掌握常用的具有关系的实体操作，实例采用大家比较熟悉的订单管理。

主要内容：

n 创建数据库表，包括订单表和订单明细表。

n 创建持久单元和实体类

n 创建管理实体类的会话Bean，添加添加订单、删除订单和察看所有订单的功能。

n 编写客户端程序进行测试。

注意：在完成第三次大作业的时候可以参考这个内容，但是不要完全按照这个做。

1、创建数据库表

订单管理包括订单表和订单明细表（正常情况下，还应该包含物品表，为了讲解方便），表定义语句如下：

create table ordertable

(

orderid char(10) not null,

orderdate date,

orderstate char(1),

userid char(10),

primary key(orderid)

);

create table orderdetail

(

orderid char(10),

goodid char(10),

quantity int,

primary key(orderid,goodid),

foreign key(orderid) references ordertable(orderid)

);

2、创建持久单元和实体类

操作过程与前面几讲的操作过程相同。

根据上面的表结构生成的实体类的代码如下。

2.1 实体类Ordertable：

package order;

import java.io.Serializable;

import java.util.Collection;

import java.util.Date;

import javax.persistence.CascadeType;

import javax.persistence.Column;

import javax.persistence.Entity;

import javax.persistence.FetchType;

import javax.persistence.Id;

import javax.persistence.NamedQueries;

import javax.persistence.NamedQuery;

import javax.persistence.OneToMany;

import javax.persistence.Table;

import javax.persistence.Temporal;

import javax.persistence.TemporalType;

@Entity

@Table(name = "ordertable")

@NamedQueries( {

@NamedQuery(name = "Ordertable.findByOrderid", query = "SELECT o FROM Ordertable o WHERE o.orderid = :orderid"),

@NamedQuery(name = "Ordertable.findByOrderdate", query = "SELECT o FROM Ordertable o WHERE o.orderdate = :orderdate"),

@NamedQuery(name = "Ordertable.findByOrderstate", query = "SELECT o FROM Ordertable o WHERE o.orderstate = :orderstate"),

@NamedQuery(name = "Ordertable.findByUserid", query = "SELECT o FROM Ordertable o WHERE o.userid = :userid")

})

public class Ordertable implements Serializable {

@Id

@Column(name = "orderid", nullable = false)

private String orderid;

@Column(name = "orderdate")

@Temporal(TemporalType.DATE)

private Date orderdate;

@Column(name = "orderstate")

private Character orderstate;

@Column(name = "userid")

private String userid;

@OneToMany(cascade = CascadeType.ALL, mappedBy = "ordertable",fetch=FetchType.EAGER)

private Collection<Orderdetail> orderdetailCollection;

/** Creates a new instance of Ordertable */

public Ordertable() {

}

public Ordertable(String orderid) {

this.orderid = orderid;

}

public String getOrderid() {

return this.orderid;

}

public void setOrderid(String orderid) {

this.orderid = orderid;

}

public Date getOrderdate() {

return this.orderdate;

}

public void setOrderdate(Date orderdate) {

this.orderdate = orderdate;

}

public Character getOrderstate() {

return this.orderstate;

}

public void setOrderstate(Character orderstate) {

this.orderstate = orderstate;

}

public String getUserid() {

return this.userid;

}

public void setUserid(String userid) {

this.userid = userid;

}

public Collection<Orderdetail> getOrderdetailCollection() {

return this.orderdetailCollection;

}

public void setOrderdetailCollection(Collection<Orderdetail> orderdetailCollection) {

this.orderdetailCollection = orderdetailCollection;

}

@Override

public int hashCode() {

int hash = 0;

hash += (this.orderid != null ? this.orderid.hashCode() : 0);

return hash;

}

@Override

public boolean equals(Object object) {

// TODO: Warning - this method won't work in the case the id fields are not set

if (!(object instanceof Ordertable)) {

return false;

}

Ordertable other = (Ordertable)object;

if (this.orderid != other.orderid && (this.orderid == null || !this.orderid.equals(other.orderid))) return false;

return true;

}

@Override

public String toString() {

return "order.Ordertable[orderid=" + orderid + "]";

}

}

2.2 实体类Orderdetail：

package order;

import java.io.Serializable;

import javax.persistence.Column;

import javax.persistence.EmbeddedId;

import javax.persistence.Entity;

import javax.persistence.JoinColumn;

import javax.persistence.ManyToOne;

import javax.persistence.NamedQueries;

import javax.persistence.NamedQuery;

import javax.persistence.Table;

@Entity

@Table(name = "orderdetail")

@NamedQueries( {

@NamedQuery(name = "Orderdetail.findByOrderid", query = "SELECT o FROM Orderdetail o WHERE o.orderdetailPK.orderid = :orderid"),

@NamedQuery(name = "Orderdetail.findByGoodid", query = "SELECT o FROM Orderdetail o WHERE o.orderdetailPK.goodid = :goodid"),

@NamedQuery(name = "Orderdetail.findByQuantity", query = "SELECT o FROM Orderdetail o WHERE o.quantity = :quantity")

})

public class Orderdetail implements Serializable {

@EmbeddedId

protected OrderdetailPK orderdetailPK;

@Column(name = "quantity")

private Integer quantity;

@JoinColumn(name = "orderid", referencedColumnName = "orderid", insertable = false, updatable = false)

@ManyToOne

private Ordertable ordertable;

public Orderdetail() {

}

public Orderdetail(OrderdetailPK orderdetailPK) {

this.orderdetailPK = orderdetailPK;

}

public Orderdetail( String orderid,String goodsid) {

this.orderdetailPK = new OrderdetailPK(goodsid, orderid);

}

public OrderdetailPK getOrderdetailPK() {

return this.orderdetailPK;

}

public void setOrderdetailPK(OrderdetailPK orderdetailPK) {

this.orderdetailPK = orderdetailPK;

}

public Integer getQuantity() {

return this.quantity;

}

public void setQuantity(Integer quantity) {

this.quantity = quantity;

}

public Ordertable getOrdertable() {

return this.ordertable;

}

public void setOrdertable(Ordertable ordertable) {

this.ordertable = ordertable;

}

@Override

public int hashCode() {

int hash = 0;

hash += (this.orderdetailPK != null ? this.orderdetailPK.hashCode() : 0);

return hash;

}

@Override

public boolean equals(Object object) {

// TODO: Warning - this method won't work in the case the id fields are not set

if (!(object instanceof Orderdetail)) {

return false;

}

Orderdetail other = (Orderdetail)object;

if (this.orderdetailPK != other.orderdetailPK && (this.orderdetailPK == null || !this.orderdetailPK.equals(other.orderdetailPK))) return false;

return true;

}

@Override

public String toString() {

return "order.Orderdetail[orderdetailPK=" + orderdetailPK + "]";

}

}

2.3 订单明细主键类：

package order;

import java.io.Serializable;

import javax.persistence.Column;

import javax.persistence.Embeddable;

@Embeddable

public class OrderdetailPK implements Serializable {

@Column(name = "orderid", nullable = false)

private String orderid;

@Column(name = "goodid", nullable = false)

private String goodid;

/** Creates a new instance of OrderdetailPK */

public OrderdetailPK() {

}

public OrderdetailPK(String goodid, String orderid) {

this.goodid = goodid;

this.orderid = orderid;

}

public String getOrderid() {

return this.orderid;

}

public void setOrderid(String orderid) {

this.orderid = orderid;

}

public String getGoodid() {

return this.goodid;

}

public void setGoodid(String goodid) {

this.goodid = goodid;

}

@Override

public int hashCode() {

int hash = 0;

hash += (this.goodid != null ? this.goodid.hashCode() : 0);

hash += (this.orderid != null ? this.orderid.hashCode() : 0);

return hash;

}

@Override

public boolean equals(Object object) {

// TODO: Warning - this method won't work in the case the id fields are not set

if (!(object instanceof OrderdetailPK)) {

return false;

}

OrderdetailPK other = (OrderdetailPK)object;

if (this.goodid != other.goodid && (this.goodid == null || !this.goodid.equals(other.goodid))) return false;

if (this.orderid != other.orderid && (this.orderid == null || !this.orderid.equals(other.orderid))) return false;

return true;

}

@Override

public String toString() {

return "order.OrderdetailPK[goodid=" + goodid + ", orderid=" + orderid + "]";

}

}

3、创建管理实体的会话Bean

在会话Bean中添加如下业务方法：

n 添加订单的方法

n 删除订单的方法

n 查询所有订单的方法

n 为订单添加订单项

3.1 添加业务方法：添加订单

public void addOrder(Ordertable order){

Ordertable newOrder = em.merge(order);

em.persist(newOrder);

}

因为通过参数传递过来的Order实体处理分离状态，所有需要先通过merge操作把该实例转换成被管理的，然后通过persist方法持久化。

注意：在持久化订单的同时，会把与订单关联的订单明细也持久化，这是通过定义管理的时候指定的“cascade”属性完成的，代码如下红色部分：

@OneToMany(cascade = CascadeType.ALL,

mappedBy = "ordertable",fetch=FetchType.EAGER)

private Collection<Orderdetail> orderdetailCollection;

cascade属性的值是CascadeType.ALL，意味着对订单类的操作，都会级联到关联的订单明细，包括下面的订单删除。

3.2 添加业务方法：删除订单

public void removeOrder(String orderid){

Ordertable order = em.find(Ordertable.class,orderid);

em.remove(order);

}

要删除订单，需要查找到该订单，然后再删除。

3.3 添加业务方法：查询所有订单

public List<Ordertable> getAllOrders(){

return em.createQuery("select o from Ordertable o").getResultList();

}

因为订单包括订单明细，所以在查询所有订单的时候，应该把该订单涉及的所有订单明细查询出来，该功能是通过定义关系的时候的fetch属性完成的，代码如下红色部分：

@OneToMany(cascade = CascadeType.ALL,

mappedBy = "ordertable",fetch=FetchType.EAGER)

private Collection<Orderdetail> orderdetailCollection;

如果不需要在加载实体的时候，加载该实体所关联的实体，可以使用FetchType.LAZY。

ManyToOne关系中，fetch属性的默认值是EAGER。

OneToOne关系中，fetch属性的默认值是EAGER。

OneToMany关系中，fetch属性的默认值是LAZY。

ManyToMany关系中，fetch属性的默认值是LAZY。

3.4 添加业务方法：添加订单项

public void addItem(String orderid,String goodsid,int quantity){

Ordertable order = em.find(Ordertable.class,orderid);

Orderdetail item = new Orderdetail(orderid,goodsid);

item.setQuantity(quantity);

if(order.getOrderdetailCollection()==null)

order.setOrderdetailCollection(new Vector<Orderdetail>());

order.getOrderdetailCollection().add(item);

item.setOrdertable(order);

}

4、编写客户端程序进行测试

分别对下面的3个功能进行测试：

n 添加订单

n 删除订单

n 察看订单

4.1 添加订单

添加订单有两种方式：

n 创建订单对象、创建订单项对象、把订单项添加到订单中，然后调用会话Bean完成添加。

n 创建订单对象，调用会话Bean完成添加，然后调用会话Bean的添加订单项方法添加具体的订单项。

下面代码中用到的remote是注入的EJB对象。

4.1.1 第一种方式

Ordertable order = new Ordertable();

String orderid="order2222";

order.setOrderid(orderid);

order.setUserid("lixucheng");

order.setOrderstate('0');

order.setOrderdate(new Date());

Vector v = new Vector();

Orderdetail od1 = new Orderdetail(orderid,"goods111");

Orderdetail od2 = new Orderdetail(orderid,"goods777");

Orderdetail od3 = new Orderdetail(orderid,"goods333");

Orderdetail od4 = new Orderdetail(orderid,"goods999");

Orderdetail od5 = new Orderdetail(orderid,"goods555");

od1.setOrdertable(order);

od2.setOrdertable(order);

od3.setOrdertable(order);

od4.setOrdertable(order);

od5.setOrdertable(order);

v.add(od1);

v.add(od2);

v.add(od3);

v.add(od4);

v.add(od5);

order.setOrderdetailCollection(v);

remote.addOrder(order);

4.1.2 第二种方式

Ordertable order = new Ordertable();

order.setOrderid("order1111");

order.setUserid("lixucheng");

order.setOrderstate('0');

order.setOrderdate(new Date());

remote.addOrder(order);

remote.addItem("order1111","goods111",10);

remote.addItem("order1111","goods222",20);

remote.addItem("order1111","goods333",30);

remote.addItem("order1111","goods444",40);

remote.addItem("order1111","goods555",50);

4.2 删除订单

删除订单需要根据订单编号删除。

remote.removeOrder("order0000");

4.3 查询所有订单及明细

List<Ordertable> list = remote.getAllOrders();

该方法调用就可以得到所有的订单以及订单的明细。

下面是在Servlet中显示订单信息的代码：

Iterator<Ordertable> i = list.iterator();

while(i.hasNext()){

Ordertable tempOrder = i.next();

out.println("订单号："+tempOrder.getOrderid()

+"订单日期："+tempOrder.getOrderdate()+" 明细：");

Iterator<Orderdetail> detail=tempOrder.getOrderdetailCollection().iterator();

while(detail.hasNext()){

Orderdetail tempDetail = detail.next();

out.println("["+tempDetail.getOrderdetailPK().getGoodid()

+","+tempDetail.getQuantity()+"]");

}

out.println("<br>");

}

更多内容可以参考《Java EE 5实用教程——基于WebLogic和Eclipse》