Java持久性API（JPA）第6講——關係操作

  

目標：通過執行個體掌握常用的具有關係的實體操作，執行個體採用大家比較熟悉的訂單管理。主要內容：n         建立資料庫表，包括訂單表和訂單明細表。n         建立持久單元和實體類n         建立管理實體類的會話Bean，添加添加訂單、刪除訂單和察看所有訂單的功能。n         編寫用戶端程式進行測試。注意：在完成第三次大作業的時候可以參考這個內容，但是不要完全按照這個做。1、 建立資料庫表訂單管理組件括訂單表和訂單明細表（正常情況下，還應該包含物品表，為了講解方便），表定義語句如下：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、 建立持久單元和實體類操作過程與前面幾講的操作過程相同。根據上面的表結構產生的實體類的代碼如下。2.1 實體類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 實體類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 訂單明細主鍵類：package order; import java.io.Serializable;import javax.persistence.Column;import javax.persistence.Embeddable; @Embeddablepublic 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、 建立管理實體的會話Bean在會話Bean中添加如下業務方法：n         添加訂單的方法n         刪除訂單的方法n         查詢所有訂單的方法n         為訂單添加訂單項3.1 添加業務方法：添加訂單    public void addOrder(Ordertable order){        Ordertable newOrder = em.merge(order);        em.persist(newOrder);}因為通過參數傳遞過來的Order實體處理分離狀態，所有需要先通過merge操作把該執行個體轉換成被管理的，然後通過persist方法持久化。注意：在持久化訂單的同時，會把與訂單關聯的訂單明細也持久化，這是通過定義管理的時候指定的“cascade”屬性完成的，代碼如下紅色部分：@OneToMany(cascade = CascadeType.ALL, mappedBy = "ordertable",fetch=FetchType.EAGER)    private Collection<Orderdetail> orderdetailCollection;cascade屬性的值是CascadeType.ALL，意味著對訂單類的操作，都會級聯到關聯的訂單明細，包括下面的訂單刪除。3.2 添加業務方法：刪除訂單    public void removeOrder(String orderid){        Ordertable order = em.find(Ordertable.class,orderid);        em.remove(order);        }要刪除訂單，需要尋找到該訂單，然後再刪除。3.3 添加業務方法：查詢所有訂單    public List<Ordertable> getAllOrders(){        return em.createQuery("select o from Ordertable o").getResultList();}因為訂單包括訂單明細，所以在查詢所有訂單的時候，應該把該訂單涉及的所有訂單明細查詢出來，該功能是通過定義關係的時候的fetch屬性完成的，代碼如下紅色部分：@OneToMany(cascade = CascadeType.ALL, mappedBy = "ordertable",fetch=FetchType.EAGER)    private Collection<Orderdetail> orderdetailCollection;如果不需要在載入實體的時候，載入該實體所關聯的實體，可以使用FetchType.LAZY。ManyToOne關係中，fetch屬性的預設值是EAGER。OneToOne關係中，fetch屬性的預設值是EAGER。OneToMany關係中，fetch屬性的預設值是LAZY。ManyToMany關係中，fetch屬性的預設值是LAZY。3.4 添加業務方法：添加訂單項    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、 編寫用戶端程式進行測試分別對下面的3個功能進行測試：n         添加訂單n         刪除訂單n         察看訂單4.1 添加訂單添加訂單有兩種方式：n         建立訂單對象、建立訂單項對象、把訂單項添加到訂單中，然後調用會話Bean完成添加。n         建立訂單對象，調用會話Bean完成添加，然後調用會話Bean的添加訂單項方法添加具體的訂單項。下面代碼中用到的remote是注入的EJB對象。4.1.1 第一種方式        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 第二種方式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 刪除訂單刪除訂單需要根據訂單編號刪除。remote.removeOrder("order0000");4.3 查詢所有訂單及明細List<Ordertable> list = remote.getAllOrders();該方法調用就可以得到所有的訂單以及訂單的明細。下面是在Servlet中顯示訂單資訊的代碼：        Iterator<Ordertable> i = list.iterator();        while(i.hasNext()){            Ordertable tempOrder = i.next();            out.println("訂單號："+tempOrder.getOrderid()+" 訂單日期："+tempOrder.getOrderdate()+" 明細：");            Iterator<Orderdetail> detail=tempOrder.getOrderdetailCollection().iterator();            while(detail.hasNext()){                Orderdetail tempDetail = detail.next();                out.println("["+tempDetail.getOrderdetailPK().getGoodid()+","+tempDetail.getQuantity()+"]");            }            out.println("<br>");

        }

更多內容可以參考《Java EE 5實用教程——基於WebLogic和Eclipse》