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編程基礎:JPA學習筆記(一)

←手機掃碼閱讀     火星人 @ 2014-03-09 , reply:0

  一般來講JPA包含以下幾個文件:

  1.pojo類

  2.映射文件

  3.持久層映射文件(Persistence units)

  1,2主要用來映射關係資料庫中的實體,3主要用來定義JPAProvide,資料庫連接定義等操作.

  下面來看具體的POJO類的寫法


 package com.liliang.entity;
  import javax.persistence.Column;
  import javax.persistence.Entity;
  import javax.persistence.GeneratedValue;
  import javax.persistence.GenerationType;
  import javax.persistence.Id;
  import javax.persistence.Version;
  import java.io.Serializable;
  import java.util.Date;
  //JPA必須擁有一個實體類,對應資料庫中的表.
  //實體類的要求是:
  //1.需要用註解的方式在類開頭聲明:@Entity()聲明
  //2.必須包含一個空的構造函數,並且必須是public或是protected修飾符.
  //3.必須是top-levle類,即enum或是interface是不可以用作當成實體類的.
  //4.不可以是final.如果實體類有可能是託管對象,那麼就必須實現Serialization介面.
  //我們使用註解的方式來實現.
  //關於註解的解釋:
  //1.@Column provides the name of the column in a table if it is different from the attribute name.
  //(By default, the two names are assumed to be the same.)
  //
  //2.JPA allows persistent classes to inherit from non-persistent classes, persistent classes to inherit from other persistent classes,
  //and non-persistent classes to inherit from persistent classes.
  //3.The entity class should have a default no-argument constructor.
  //4.The entity class should not be final.
  //5.Persistent classes cannot inherit from certain natively-implemented system classes such as java.net.Socket and java.lang.Thread.
  //6.If a persistent class inherits from a non-persistent class, the fields of the non-persistent super class cannot be persisted.
  @Entity(name="Customer")
  public class Customer implements Serializable {
  /**
  * 主機自動生成
  */
  private static final long serialVersionUID = -4020535715918096623L;
  @Id //代表主鍵
  @Column(name="CUST_ID",nullable=false) //映射表中的一列
  @GeneratedValue(strategy = GenerationType.AUTO) //標示符生成策略
  private Integer custId;
  @Column(name="FIRST_NAME",nullable=true,length=50)
  private String first_Name;
  @Column(name="LAST_NAME",nullable=false,length=50)
  private String last_Name;
  @Column(name="STREET",nullable=false,length=50)
  private String street;
  @Column(name="APPT",nullable=true,length=20)
  private String appt;
  @Column(name="CITY",nullable=false,length=25)
  private String city;
  @Column(name="ZIP_CODE",nullable=true,length=10)
  private String zipCode;
  @Column(name="CUST_TYPE",nullable=true,length=10)
  private String custType;
  @Version
  @Column(name="LAST_UPDATE_TIME",nullable=true)
  private Date updateTime;
  //默認
  Customer() Customer(){};
  //最小填充
  Customer() Customer(Integer custId, String last_Name, String street, String city){
  this.custId = custId;
  this.last_Name = last_Name;
  this.street = street;
  this.city = city;
  }
  //getter and setter method

  好了,下面來看映射文件的寫法


  <?xml version="1.0" encoding="UTF-8"?>
<!--
1.該xml文件可以包含多個persistent元素,每個元素都可以定義自己的持久層實現類和資料庫 2.實體類在<class>標籤中聲明
-->
<persistence xmlns="http://java.sun.com/xml/ns/persistence"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/persistence
http://java.sun.com/xml/ns/persistence/persistence_1_0.xsd"
version="1.0">

<persistence-unit name="testjpa" transaction-type="RESOURCE_LOCAL">
<!-- 使用OpenJPA持久層實現 -->
<!--
Provider class that supplies EntityManagers for this persistence unit
-->
<provider>
org.apache.openjpa.persistence.PersistenceProviderImpl
</provider>
<!-- 映射實體類 -->
<class>com.liliang.entity.Customer</class>
<!-- A list of vendor-specific properties. -->
<properties>
<property name="openjpa.ConnectionURL" value="jdbc:mysql://localhost:3306/hibernate" />
<property name="openjpa.ConnectionDriverName" value="com.mysql.jdbc.Driver" />
<property name="openjpa.ConnectionUserName" value="root" />
<property name="openjpa.ConnectionPassword" value="1d280478" />
<property name="openjpa.Log" value="SQL=TRANCE" />
</properties>
</persistence-unit>

</persistence>

  本文出自 「stoneli88」 博客http://stoneli88.blog.51cto.com/333387/215209


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