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JPA概要

paulwong — Sat, 04 Jun 2016 08:08:00 GMT

1 JPA概述

JPA�Q�Java Persistence API�Q�Java持久化API�Q�，定义了对�?关系映射�Q�ORM�Q�以及实体对象持久化的标准接口�?/p>

JPA是JSR-220�Q�EJB3.0�Q�规范的一部分�Q�在JSR-220中规定实体对象（EntityBean�Q�由JPA�q�行支持�?/p>

所以JPA不局限于EJB3.0�Q�而是作�ؓPOJO持久化的标准规范�Q�可以脱��d��器独立运行，开发和��试更加方便�?/p>

JPA在应用中的位�|�如下图所�C�：

JPA�l�护一个Persistence Context�Q�持久化上下文）�Q�在持久化上下文中维护实体的生命周期。主要包含三个方面的内容�Q?/p>

ORM元数据。JPA支持annotion或xml两种形式描述对象-关系映射�?/li>
实体操作API。实现对实体对象的CRUD操作�?/li>
查询语言。约定了面向对象的查询语�a�JPQL�Q�Java Persistence Query Language�Q��?/li>

JPA的主要API都定义在javax.persistence包中。如果你熟悉Hibernate�Q�可以很�Ҏ��做出对应�Q?/p>


org.hibernate	javax.persistence	说明
cfg.Configuration	Persistence	��d��配置信息
SessionFactory	EntityManagerFactory	用于创徏会话/实体��理器的工厂�c?/td>
Session	EntityManager	提供实体操作API�Q�管理事务，创徏查询
Transaction	EntityTransaction	��理事务
Query	Query	执行查询

2 实体生命周期

实体生命周期是JPA中非帔R��要的概念�Q�描�q�C��实体对象从创建到受控、从删除到游��ȝ��状态变换。对实体的操作主要就是改变实体的状态�?/p>

JPA中实体的生命周期如下图：

New�Q�新创徏的实体对象，没有主键(identity)�?/li>
Managed�Q�对象处于Persistence Context(持久化上下文�Q�中�Q�被EntityManager��理
Detached�Q�对象已�l�游��d��Persistence Context之外�Q�进入Application Domain
Removed, 实体对象被删�?/li>

EntityManager提供一�p�d��的方法管理实体对象的生命周期�Q�包括：

persist, ��新创徏的或已删除的实体转变为Managed状态，数据存入数据库�?/li>
remove�Q�删除受控实�?/li>
merge�Q�将游离实体转变为Managed状态，数据存入数据库�?/li>

如果使用了事务管理，则事务的commit/rollback也会改变实体的状态�?/p>

3 实体关系映射�Q�ORM�Q?/h2>
3.1 基本映射

对象�?/th> 数据库端 annotion 可选annotion
Class Table @Entity @Table(name="table_name")
property column – @Column(name = "column_name")
property primary key @Id @GeneratedValue 详见ID生成�{�略
property NONE @Transient
3.2 ID生成�{�略
ID对应数据库表的主键，是保证唯一性的重要属性。JPA提供了以下几�U�ID生成�{�略
GeneratorType.AUTO �Q�由JPA自动生成
GenerationType.IDENTITY�Q��用数据库的自增长字段�Q�需要数据库的支持（如SQL Server、MySQL、DB2、Derby�{�）
GenerationType.SEQUENCE�Q��用数据库的序列号�Q�需要数据库的支持（如Oracle�Q?/li>
GenerationType.TABLE�Q��用指定的数据库表记录ID的增�?需要定义一个TableGenerator�Q�在@GeneratedValue中引用。例如：
@TableGenerator( name="myGenerator", table="GENERATOR_TABLE", pkColumnName = "ENTITY_NAME", pkColumnValue="MyEntity", valueColumnName = "PK_VALUE", allocationSize=1 )
@GeneratedValue(strategy = GenerationType.TABLE,generator="myGenerator")
3.3 兌��关系
JPA定义了one-to-one、one-to-many、many-to-one、many-to-many 4�U�关�p�R�?/p>
对于数据库来��_��通常在一个表中记录对另一个表的外键关联；对应到实体对象，持有兌��数据的一方称为owning-side�Q�另一方称为inverse-side�?/p>
��Z��~�程的方便，我们�l�常会希望在inverse-side也能引用到owning-side的对象，此时��构��Z��双向兌��关系�?在双向关联中�Q�需要在inverse-side定义mappedBy属性，以指明在owning-side是哪一个属性持有的兌��数据�?/p>
对关联关�p�L��的要点如下�Q?/p>

关系�c�d�� Owning-Side Inverse-Side
one-to-one @OneToOne @OneToOne(mappedBy="othersideName")
one-to-many / many-to-one @ManyToOne @OneToMany(mappedBy="xxx")
many-to-many @ManyToMany @ManyToMany(mappedBy ="xxx")
其中 many-to-many关系的owning-side可以使用@JoinTable声明自定义关联表�Q�比如Book和Author之间的关联表�Q?/p>
@JoinTable(name = "BOOK_AUTHOR", joinColumns = { @JoinColumn(name = "BOOK_ID", referencedColumnName = "id") }, inverseJoinColumns = { @JoinColumn(name = "AUTHOR_ID", referencedColumnName = "id") })
兌��关系�q�可以定制�g�q�加载和�U�联操作的行为（owning-side和inverse-side可以分别讄��Q�：
通过讄��fetch=FetchType.LAZY �?fetch=FetchType.EAGER来决定关联对象是延迟加蝲或立卛_��载�?/p>
通过讄��cascade={options}可以讄��U�联操作的行为，其中options可以是以下组合：
CascadeType.MERGE �U�联更新
CascadeType.PERSIST �U�联保存
CascadeType.REFRESH �U�联��h��
CascadeType.REMOVE �U�联删除
CascadeType.ALL �U�联上述4�U�操�?/li>
3.4 �l�承关系
JPA通过在父�c�d��加@Inheritance(strategy=InheritanceType.xxx)来声明��承关�p�R��A支持3�U��承策略：
单表�l�承�Q�InheritanceType.SINGLE_{TABLE�Q�，所有��承树上的�c�d��用一张表�Q�在父类指定�Q?/sub>@DiscriminatorColumn�Q�声明�ƈ在每个类指定@DiscriminatorValue来区分类型�?/li>}
�c�表�l�承�Q�InheritanceType.JOINED�Q�，父子�c�d��同的部分公用一张表�Q�其余部分保存到各自的表�Q�通过join�q�行兌��?/li>
具体表��承（InheritanceType.TABLE_PER_CLASS)�Q�每个具体类映射到自��q��表�?/li>
其中1�?能够支持多态，但是1需要允许字�D��ؓNULL�Q?需要多个JOIN关系�Q?最适合关系数据库，对多态支持不好。具体应用时�Ҏ��需要取舍�?/p>

对象�?/th>	数据库端	annotion	可选annotion
Class	Table	@Entity	@Table(name="table_name")
property	column	–	@Column(name = "column_name")
property	primary key	@Id	@GeneratedValue 详见ID生成�{�略
property	NONE	@Transient

关系�c�d��	Owning-Side	Inverse-Side
one-to-one	@OneToOne	@OneToOne(mappedBy="othersideName")
one-to-many / many-to-one	@ManyToOne	@OneToMany(mappedBy="xxx")
many-to-many	@ManyToMany	@ManyToMany(mappedBy ="xxx")

4 事�g及监�?/h2>
通过在实体的�Ҏ��上标注@PrePersist�Q�@PostPersist�{�声明即可在事�g发生时触发这些方法�?/p>

5 Query Language 查询语言

JPA提供两种查询方式�Q�一�U�是�Ҏ��主键查询�Q��用EntityManager的find�Ҏ��Q?/p>

T find(Class entityClass, Object primaryKey)

另一�U�就是��用JPQL查询语言。JPQL是完全面向对象的�Q�具备��ѝ��多态和兌��{�特性，和hibernate HQL很相伹{�?/p>

使用EntityManager的createQuery�Ҏ��Q?/p>

Query createQuery(String qlString)

5.1 使用参数

可以在JPQL语句中��用参数。JPQL支持命名参数和位�|�参��C��U�参敎ͼ�但是在一条JPQL语句中所有的参数只能使用同一�U�类型�?/p>

举例如下�Q?/p>

命��o参数

Query query = em.createQuery("select p from Person p where p.personid=:Id"); query.setParameter("Id",new Integer(1));

位置参数

Query query = em.createQuery("select p from Person p where p.personid=?1"); query.setParameter(1,new Integer(1));

5.2 命名查询

如果某个JPQL语句需要在多个地方使用�Q�还可以使用@NamedQuery 或�?@NamedQueries在实体对象上预定义命名查询�?/p>

在需要调用的地方只要引用该查询的名字卛_��?/p>

例如�Q?/p>

@NamedQuery(name="getPerson", query= "FROM Person WHERE personid=?1")

@NamedQueries({ @NamedQuery(name="getPerson1", query= "FROM Person WHERE personid=?1"), @NamedQuery(name="getPersonList", query= "FROM Person WHERE age>?1") })

Query query = em.createNamedQuery("getPerson");

5.3 排序

JPQL也支持排序，�c�M��于SQL中的语法。例如： Query query = em.createQuery("select p from Person p order by p.age, p.birthday desc");

5.4 聚合查询

JPQL支持AVG、SUM、COUNT、MAX、MIN五个聚合函数。例如：

Query query = em.createQuery("select max(p.age) from Person p"); Object result = query.getSingleResult(); String maxAge = result.toString();

5.5 更新和删�?/h3>
JPQL不仅用于查询�Q�还可以用于扚w��更新和删除�?/p>
如：
Query query = em.createQuery("update Order as o set o.amount=o.amount+10"); //update 的记录数 int result = query.executeUpdate();
Query query = em.createQuery("delete from OrderItem item where item.order in(from Order as o where o.amount<100)"); query.executeUpdate();
query = em.createQuery("delete from Order as o where o.amount<100"); query.executeUpdate();//delete的记录数

5.6 更多

与SQL�c�M��Q�JPQL�q�涉及到更多的语法，可以参考：http://docs.oracle.com/cd/E11035_01/kodo41/full/html/ejb3_langref.html

6 事务��理

JPA支持本地事务��理�Q�RESOURCE_{LOCAL�Q�和容器事务��理�Q�JTA�Q�，容器事务��理只能用在EJB}/Web容器环境中�?/p>

事务��理的类型可以在persistence.xml文�g中的“transaction-type”元素配置�?/p>

JPA中通过EntityManager的getTransaction()�Ҏ��获取事务的实例（EntityTransaction�Q�，之后可以调用事务的begin()、commit()、rollback()�Ҏ��?/p>

Date: 2012-12-30 16:46:29 CST

Author: Holbrook

Org version 7.8.11 with Emacs version 24

paulwong 2016-06-04 16:08 发表评论

paulwong — Fri, 07 Jun 2013 07:09:00 GMT

一套S2SH的应用，现用单线�E�，�q�箋�?000个请求，用的DBCP链接池，�l�果报数据库链接不够用：

ERROR [org.hibernate.util.JDBCExceptionReporter] - Cannot get a connection, pool error Timeout waiting for idle object

在JAVA加上LOG�Q?br />

log.info("active: " + dataSource.getNumActive() + " (max: "
+ dataSource.getMaxActive() + ") " + "idle: " + dataSource.getNumIdle()
+ "(max: " + dataSource.getMaxIdle() + ")");

�l�果昄��为：

active: 25 (max: 100) idle: 0(max: 30)

active的数量一直增加，但idle的数量一直�ؓ0。当�E�序向链接池要链接的时候，如果池没有，��׃��新徏一个，active数就会加1�Q�关闭链接后�Q�链接会�q�回池，idle数加1。idle�?则表�C�池里没有链接�?br />
�q�样说明链接一直在创徏�Q�没有关闭放回池里。但链接是由SPRING和HIBERNATE��理的，代码中没有关闭链接的语句。之后试了N多配�|�，都还没解冻I��如增加maxActive数等。最后，加上�q�一行，问题才终于解冻I��

<prop key="hibernate.connection.release_mode">after_transactionprop>

�q�里默认值是auto�Q�如果是用JTA事务才适用�Q�如果是JDBC事务�Q�就只能用after_transaction�?br />
�q�样每次事务�l�束后，��׃��关闭链接�q�回链接池�?br />

paulwong 2013-06-07 15:09 发表评论

Hibernate Tools

paulwong — Sun, 10 Jun 2012 02:21:00 GMT

Hibernate Tools是由JBoss推出的一个Eclipse�l�合开发工��h��Ӟ��该插件可以简化ORM框架Hibernate�Q�以及JBoss Seam�Q�EJB3�{�的开发工作。Hibernate Tools可以以Ant Task以及Eclipse插�g的�Ş式运行�?br />

Hibernate Tools Eclipse插�g的特�?/h3>Hibernate Tools Eclipse插�g��h��以下特征或功能：
Mapping Editor�Q�映��文件编辑器�Q�：该编辑器可以用来�~�辑Hibernate XML映射文�g�Q�提供代码自动补全，语法高亮功能�?
- �c�d��的自动补�?
- 属�?表的列名自动补全

Hibernate Console�Q�Hibernate控制収ͼ��Q?/strong>它提供一个全新的Eclipse Perspective�H�口�Q�可以执行HQL�Q��ƈ查看查询的结果。这是一个非�怾�利的工具�Q�可以用来验证HQL的语法是否正��?

Configuration Wizards and Code generation�Q�Hibernate配置文�ghibernate.cfg.xml创徏��D��Q�以及代码生成器�Q�：�?持完全反向生成功能，可以从已有的数据库生成Hibernate配置文�ghibernate.cfg.xml�Q�同时支�?click-and- generate"方式生成Java代码(Hibernate POJOs)�Q�DAO�Q�XML映射文�g�Q?hbm.xml�Q�，以及schema 文档�Q?hml�Q�等文�g�?

Eclipse JDT integration�Q�代码补全）�Q?/strong>该工��h��持Java代码中的HQL输入补全�Q�以及对Java代码中的HQL语法加以合法性验证�?

Hibernate Tools的��?/h3>- Hibernate的配�|�文件hibernate.cfg.xml的生�?/strong>
步骤�Q?
1�Q�Eclipse的菜单：选择[File] -> [New] -> [Other] -> [Hibernate/Hibernate Configuration file (cfg.xml) ]�Q?#8220;Next”按钮
2�Q�输�?[Database dialect] �Q�[Driver Class]�Q�[Connection URL]�Q�以及[DB用户名]�Q�[密码]�{?
3�Q�按下[Finish]按钮�Q�则自动生成hibernate.cfg.xml文�g�?
"Create Console Configuration" checkbox默认为选择状态。被选择的情况下�Q�则�q�入“Hibernate Console Configuration ”�Q�Hibernate Console�Q�设�|?创徏��面�?

- 讄��Hibernate Console
Hibernate Tools支持创徏多个Hibernate Console�?
1�Q�Eclipse菜单�Q�选择[File] -> [New] -> [Other] -> [Hibernate/Hibernate Console Configuration]�Q?#8220;Next”按钮
2�Q�在所昄��的画面上输入Hibernate Console的名�U�[Name]�Q�目标项目名[Project]�Q�Hibernate配置文�g�Q�hibernate.cfg.xml�Q�的路径[Configuration file]
3�Q�按[Finish]按钮�Q�则创徏Hibernate Console�Q�同时显�C�在"Hibernate Configurations"视图中�?

- Reverse engineering and code generation�Q?/strong>利用"click-and-generate" Reverse Engineering以及代码生成功能自动生成所需代码�?
※使用Hibernate code generation�Q�Hibernate代码生成器）之前�Q�需要先配置/创徏Hibernate Console�?
1�Q�可以从Hibernate 的Tool Bar�Q�或"Run/Hibernate Code Generation"菜单启动Hibernate代码生成器�?
2�Q�在所昄��的画面上�Q�输�?创徏好的Hibernate控制台名�U�[Console Configuration]�Q�输��\径「Output directory」等信息�?
其它可以实际情况加以讄��?
3�Q�打开Explore标签�Q�设�|�需要生成的代码�c�d��Q�Domain code, DAO�{�）
4�Q�设�|�完成之后，按下[Run]按钮
�Ҏ��不同的配�|�，��自动生成Hibernate兌��文�g�Q�EJB3�Q�JBoss Seam�{�文件�?

Hibernate Tools其它参考资�?/h3>Hibernate Tools Reference Guide [官方文档]
Hibernate Tools Eclipse Plugins [官方文档�Q�Hibernate Tools Eclipse插�g]

paulwong 2012-06-10 10:21 发表评论

paulwong — Thu, 19 Apr 2012 09:56:00 GMT

在进行SELECT操作�Ӟ��通常接下来会�q�行UPADTE的操作，如果希望COMMIT前，所SELECT的数据不会被其他�U�程SELECT出来�Q�则两个�U�程都加FOR UPDATE/FOR UPDATE NOWAIT关键字，�q�样数据库就会锁定这些记录，加了FOR UPDATE的会�q�行�{�待�Q�直��C��一�U�程�l�束�Q�加了FOR UPDATE NOWAIT的线�E�则直接抛出异常�Q�这�U�机制称为数据库的锁机制�?/div>
HIBERNATE中的实现�Q?br />
LockMode.NONE �Q�有�~�存用缓存，没缓存则从数据库�?nbsp;
LockMode.READ �Q�直接从数据库读�Q�不使用�~�存数据
LockMode.WRITE �Q�在insert update数据的时候，HIBERNATE内部使用的�?nbsp;
以上3�U�均为HIBERNATE�U�别的锁�Q�也��是�~�存�U�别的锁�?nbsp;

下面2�U��ؓ数据库��别的锁：
LockMode.UPGRADE�Q�相当于SQL语句select for update�Q�被select的数据都被数据库锁住了，不能被其他事务修攏V�?nbsp;
LockMode. UPGRADE_NOWAIT �Q�是ORACLE数据库特有的select for update nowait

paulwong 2012-04-19 17:56 发表评论

Using an Example of Sharding with Hibernate

paulwong — Wed, 04 Jan 2012 15:21:00 GMT

AMAZON的关于HIBERNATE SHARD的例子：
http://aws.amazon.com/articles/0040302286264415

paulwong 2012-01-04 23:21 发表评论

HIBERNATE SHARD

paulwong — Wed, 04 Jan 2012 14:40:00 GMT
数据上千万，都挤在一个表里，��D��查询太慢�Q�分库分表洛�Q�但已经用了HIBERNATE了，不想转其他框�Ӟ��用HIBERNATE SHARD!

在向大家详细介绍Hibernate Shard三种�{�略之前�Q�首先让大家了解下Hibernate Shard��介，然后全面介绍Hibernate Shard三种�{�略�?

1. Hibernate Shard��?/strong>
Hibernate Shard多数据库水��^分区解决�Ҏ��。Hibernate 的一个扩展，用于处理多数据库水��^分区架构。由google工程�?2007�q?捐献�l?Hibernate�C�֌�。目前版本： 3.0.0 beta2�Q?未发GA版。条�Ӟ��Hibernate Core 3.2�Q?JDK 5.0

2. 水��^分区原理
一个库表如 Order 存在于多个数据库实例上。按特定的分区逻辑�Q�将该库表的数据存储在这些实例中�Q�一条记录的主键 PK�Q�在所有实例中不得重复。水�q�_��区在大型�|�站�Q�大型企业应用中�l�常采用。目的出于�v量数据分散存储，分散操作�Q�分散查询以便提高数据处理量和整体数据处理性能。��用：google工程师的设计�q�是非常好的�Q�完全兼�?Hibernate本��n的主要接口�?
org.hibernate.Session
org.hibernate.SessionFactory
org.hibernate.Criteria
org.hibernate.Query

因此�E�序员开发变化不大，甚至不需要关心后��C��用了分区数据库。程序迁�U�问题不大。而且配置上比较简明�?

3. Hibernate Shard三种�{�略�Q?/strong>
◆ShardAccessStrategy�Q?查询操作�Ӟ��到那个分区执行。默认提供两个实玎ͼ�
��序�{�略�Q�SequentialShardAccessStrategy�Q?每个query按顺序在所有分��Z��执行�?br />�q��{�略�Q�ParallelShardAccessStrategy�Q?每个query以多�U�程方式�q�发�q��的在所有分��Z��执行。此�{�略下，需要��用线�E�池机制满��特定的性能需要，java.util.concurrent.ThreadPoolExecutor.

◆ShardSelectionStrategy�Q?新增对象�Ӟ��存储到哪个分区。框枉��认提供了一个轮询选择�{�略 RoundRobinShardSelectionStrategy�Q?但一般不�q�样使用。通常采用“attribute-based sharding”机制�Q�基于属性分区。一般是用户�Ҏ��表自己实��C��个基于属性分区的�{�略�c�ShardSelectionStrategy �Q�例如，以下WeatherReport��Z��continent属性选择分区�Q?
public class WeatherReportShardSelectionStrategy implements ShardSelectionStrategy {
public ShardId selectShardIdForNewObject(Object obj) {
if(obj instanceof WeatherReport)
{
return ((WeatherReport)obj).getContinent().getShardId();
}
throw new IllegalArgumentException();
}

◆ShardResolutionStrategy�Q?该策略用于查扑֍�个对象时�Q�判断它在哪个或哪几个分��Z��。默认��?AllShardsShardResolutionStrategy �Q�可以自定义例如�Q?nbsp;

public class WeatherReportShardResolutionStrategy extends AllShardsShardResolutionStrategy
{
public WeatherReportShardResolutionStrategy(List<ShardId> shardIds)
{
super(shardIds);
}

public List<ShardId> selectShardIdsFromShardResolutionStrategyData( ShardResolutionStrategyData srsd)
{
if(srsd.getEntityName().equals(WeatherReport.class.getName()))
{
return Continent.getContinentByReportId(srsd.getId()).getShardId();
}
return super.selectShardIdsFromShardResolutionStrategyData(srsd);
}
}

paulwong 2012-01-04 22:40 发表评论

Hibernate Generic D.A.O. Framework

paulwong — Fri, 25 Nov 2011 20:23:00 GMT

The motivation behind the framework

We had worked on a project where we hand-coded all of our DAOs. This produced four irksome difficulties: (1) Method names and implementations were not altogether consistent. (2) It was a pain to make additional columns sortable or filterable, and as a result, a lot of pages lacked good sorting and filtering. (3) Making additional DAOs was tedious and took a fair amount of time. (4) Writing tests for DAOs is tricky and tedious, so no one really did.

This framework aims to ease our troubles.

Why might you consider looking into this framework?

Generic DAO: With the sweetness of Java generics, the concept of generic DAOs is not new, and it’s not difficult. However, we’ve put a lot of work into making these easy to use and robust. So if you like the way we’ve done it, then this framework provides ready-made code for you. On the other hand if you’d rather make your own, then simply feel free to look at our source code for ideas and help on a few potentially tricky issues.

Search: Search is the most original and sophisticated part of this framework, and it can be used with or without the generic DAO portion of the framework. The search capability is designed around the use-case of a list page with sorting, filtering, column selection and paging. However, its use is certainly not limited to that. The value that the search adds is simpler, more robust querying with less coding and less testing. It is similar to Hibernate Criteria, but it is simpler to use and can easily move across layers of an application including view and even remote layers. Plus is works with both Hibernate and JPA^*.

Remote DAO (for R.I.A.s?): If you you’re like us, you don’t want to write and configure an individual DAO style remote service for each entity in a R.I.A. or other client-heavy application. This framework may have the solution. We provide utilities and sample code to adapt our single general DAO to any remoting technology interface. Just configure this single remote access point and the client can do any basic CRUD or search operation on any entity. Again, if you don’t like our way of doing things, maybe you can at least get some ideas from our source code.

Remote Search (for R.I.A.s?): As mentioned above, the framework can provide a single point for client-server CRUD and search operations. The framework’s search is meant to be able to cross the client-server boundary. So lists and searches in the client application can take advantage of the same easy-to-use features and consistency that the search functionality provides in the server tier or single tier application. This consistency allowed us to create a reusable collection type in Adobe Flex 3 that is associated with a single search object and automatically updates itself from the server according to the search parameters.^**

^*A fairly simple adapter is required for each JPA provider. Right now we only have an adapter for Hibernate Entity Manager. If anyone would like to contribute an adapter for any other JPA provider (OpenJPA, TopLink, etc.), that would be great.

^**If time permits, we would like to eventually post our corresponding Adobe Flex 3 framework and utilities.

More Information

Wiki Documentation: UserGuide

Javadoc: http://hibernate-generic-dao.googlecode.com/svn/trunk/docs/api/index.html

Blog: http://hibernategenericdao.wordpress.com/

Questions and Comments

Please post at http://groups.google.com/group/java-generic-dao.

Code Examples

Creating DAOs for individual model classes:

Simply extend the GenericDAO class with the specific type.

public interface ProjectDAO extends GenericDAO<Project, Long> {

}

public class ProjectDAOImpl extends GenericDAOImpl<Project, Long> implements ProjectDAO {

}

The following methods (and several more) are now available on ProjectDAO

Project project = projectDAO.find(projectId);
List<Project> list = projectDAO.findAll();
projectDAO.save(project);
projectDAO.remove(project);
projectDAO.removeById(project.getId());

Search search = new Search();
search.addFilterEqual("name", "hibernate-generic-dao");
List<Project> list = projectDAO.search(search);

int count = projectDAO.count(search);
SearchResult<Project> result = projectDAO.searchAndCount(search);
list = result.getResult();
count = result.getTotalCount();
search.clear();
search.addField("rating", Field.OP_AVG);
int avgProjectRating = (Integer) prjoectDAO.searchUnique(search);

A GeneralDAO is also provided with DAO methods for any entity:

public interface GeneralDAO {
public <T> T find(Class<T> type, Serializable id);
public <T> T[] find(Class<T> type, Serializable ids);
public <T> T getReference(Class<T> type, Serializable id);
public <T> T[] getReferences(Class<T> type, Serializable ids);
public boolean save(Object entity); public boolean[] save(Object entities);
public boolean remove(Object entity); public void remove(Object entities);
public boolean removeById(Class type, Serializable id);
public void removeByIds(Class type, Serializable ids);
public <T> List<T> findAll(Class<T> type);
public List search(ISearch search); public Object searchUnique(ISearch search);
public int count(ISearch search); public SearchResult searchAndCount(ISearch search);
public boolean isAttached(Object entity);
public void refresh(Object entities); public void flush();
public Filter getFilterFromExample(Object example);
public Filter getFilterFromExample(Object example, ExampleOptions options); }

Search DTO usage examples

Search search = new Search(Project.class);

//filtering
search.addFilterEqual("name", "hibernate-generic-dao");

search.addFilterLessThan("completionDate", new Date());

search.addFilterOr(
Filter.equal("name", "Jack"),
Filter.and(
Filter.equal("name", "Jill"),
Filter.like("location", "%Chicago%"),
Filter.greaterThan("age", 5) )
);

search.addFilterIn("name", "Jack", "Jill", "Bob");

search.addFilterNot(Filter.in("name","Jack", "Jill", "Bob"));

//sorting
search.addSort("name");
search.addSort("age", true); //descending

//projection
search.addField("name");
search.addField("location");

//or with column operators
search.addField("rating", Field.OP_AVG);
search.addField("developerCount", Field.OP_MAX);

//paging
search.setMaxResults(15); //a.k.a. results per page
search.setPage(3);

//controlling eager fetching of relationships
serach.addFetch("owner");

Nested properties are also fully supported...

search.addFilterEqua("status.name", "active");
search.addFilterGreaterThan("workgroup.manager.salary", 75000.00);
search.addSort("status.name");

paulwong 2011-11-26 04:23 发表评论

JPA使用memcached�?�U�缓存的配置

paulwong — Wed, 16 Feb 2011 03:10:00 GMT

1.加入hibernate�Q�memcached.jar及相关jar�?br /> hibernate-memcached需要支持的�c�d��如下:
hibernate-memcached-.jar ,
memcached-2.1.jar
spy-2.4.jar
commons-codec 1.3 .
slf4j-1.5.0.jar 如果你的��目使用的是Log4j,可以�?slf4j-log4j12-1.5.0.jar

2.在applicationContext.xml中配�|?

<bean id="entityManagerFactory"
        class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean">
        <property name="dataSource" ref="dataSource" />
        <property name="jpaVendorAdapter">
            <bean
                class="org.springframework.orm.jpa.vendor.HibernateJpaVendorAdapter">
                <property name="showSql" value="${jpa.showSql}" />
                <property name="generateDdl" value="${jpa.generateDdl}" />
                <property name="database">
                    <util:constant
                        static-field="org.springframework.orm.jpa.vendor.Database.ORACLE" />
                property>
            bean>
        property>
        <property name="jpaProperties">
            <props>
                <prop key="hibernate.max_fetch_depth">3prop>
                <prop key="hibernate.cache.use_second_level_cache">
                    true
                prop>
                <prop key="hibernate.cache.use_structured_entries">
                    true
                prop>
                <prop key="hibernate.cache.use_query_cache">trueprop>
                <prop key="hibernate.cache.provider_class">
                    com.googlecode.hibernate.memcached.MemcachedCacheProvider
                prop>
                <prop key="hibernate.memcached.servers">
                    10.1.19.132:33001 10.1.19.132:33002 10.1.19.132:33003
                prop>
            props>
        property>
    bean>

3.在实体类上配�|�缓存策�?br />

@org.hibernate.annotations.Cache(usage =CacheConcurrencyStrategy.READ_WRITE)

下面�q�几�U�情况就不适合加蝲��C��U�缓存中:
1.�l�常被修改的数据
2.�l�对不允许出现�ƈ发访问的数据
3.与其他应用共享的数据
下面�q�己�U�情况合适加载到二��~�存�?
1.数据更新频率�?
2.允许偶尔出现�q�发问题的非重要数据
3.不会被�ƈ发访问的数据
4.帔R��数据
5.不会被第三方修改的数�?

paulwong 2011-02-16 11:10 发表评论

Hibernate 的session.createCriteria用法

paulwong — Fri, 03 Jul 2009 06:24:00 GMT
某一对象的配�|�文�Ӟ��

<many-to-one name="partyTypeBean" column="NATT_ID"
            class="com.paul..PartyTypeBean"
            cascade="none" outer-join="true" not-found="ignore" lazy="false"/>

如果查询Party�Q�则其关联对象PartyTypeBean是以outer-join的方式取�Q�若要覆盖这�U�方式，可采用徏别名的方式，如下�Q?br />

Criteria criteria = session.createCriteria(PartyBean.class)
                                   .createAlias("partyTypeBean", "partyTypeBean", Criteria.INNER_JOIN)
                                   .createAlias("cafBean", "cafBean", Criteria.LEFT_JOIN)
                                   .createAlias("countryBean", "countryBean", Criteria.INNER_JOIN)
                                   ;

paulwong 2009-07-03 14:24 发表评论

paulwong — Fri, 08 May 2009 05:50:00 GMT
使用APACHE的LANG包中的相关类�Q�可��写很多�?br />

    public String toString() {
        return ToStringBuilder.reflectionToString(this,
                ToStringStyle.MULTI_LINE_STYLE);
    }

    public boolean equals(Object o) {
        return EqualsBuilder.reflectionEquals(this, o);
    }

    public int hashCode() {
        return new HashCodeBuilder(17, 37)
                    .append(id)
                    .append(name)
                    .append(state)
                    .toHashCode();
    }

如果PO中有SET的集合对象，�q�且配置了HIBERNATE中的lazy="true"�Q�则��HASHCODE不能用反��的�Ҏ��Q�只能一个属性一个属性的累加计算HASHCODE�Q�集合SET不算HASHCODE�Q�否则会抛LazyInitializationException。��承的子类可以用这�U�方法加以覆盖：

public int hashCode() {
        return new HashCodeBuilder(17, 37)
                    .appendSuper(super.hashCode())
                    .append(code)
                    .toHashCode();
    }

paulwong 2009-05-08 13:50 发表评论

HIBERNATE中的对象设计

paulwong — Fri, 01 May 2009 03:57:00 GMT
zRoom与User存在一对多的关�p�，如果要在取得Room的同时取得User�Q�则在Room中加入Set�Q�List或Map�c�d��的集合成员，Set中的元素不可以重复，List中的元素可以重复�Q�Map是鍵值对�c�d��的集合�?br />
在HIBERNATE的配�|�文件中象这样配�|�：

<set name="users" table="user" cascade="all" inverse="true" lazy="extra">
            <key column="room_id"/>
            <one-to-many class="paul.com.User"/>
set>

指定users�U�有成员的类型�ؓSET�Q?span style="color: #800000">set name="users"
指定集合中的对象�c�d��为User:<one-to-many class="paul.com.User"/>
指定User对应的表�Q?span style="color: #ff0000">table="user"
指定外键�Q?span style="color: #0000ff"><key column="room_id"/>
指定如果同时新增、修攏V��删除关联的Room和User对象�Ӟ��是否需要HIBERNATE执行两次操作�Q?span style="color: #ff0000">cascade="all"
指定 lazy="extra"�?/span>�Q�则集合中的元素不会被一起取出，而且要读SIZE�Ӟ��只会发送一条COUNT的SQL语句臛_��?
指定 inverse="true"�Ӟ��当保存一的对象时�Q�对应的多的对象不会同时被保存�?/li>

如果要在取得User对象的同时取得Room对象�Q�则在User中加入私有成员Room�Q�在HIBERNATE的配�|�文件中如下配置�Q?br />

<many-to-one name="room"
             column="room_id"
             class="paul.com.Room"
             cascade="all"
             outer-join="true"/>

指定名称为room成员的类型：many-to-one name="room"
指定room对应的类名：class="paul.com.Room"
指定外键�Q?span style="color: #ff0000">column="room_id"
指定如果同时新增、修攏V��删除关联的Room和User对象�Ӟ��是否需要HIBERNATE执行两次操作�Q?span style="color: #ff0000">cascade="all"
指定兌��两个表时的查询是否��用left-outer关键字：outer-join="true"

User和Server是多对多的关�p�，如要在取得User对象的同时取得Server�Q�可以User中加入Set�U�有成员�Q�在HIBERNATE中如下配�|�：

<set name="servers"
             table="user_server"
             cascade="save-update">

            <key column="user_id"/>
            <many-to-many class="paul.com.Server"
                          column="server_id"/>
set>

指定名称为servers的私有成员的�c�d��为SET�Q?span style="color: #800000">set name="servers"

指定中间表�ؓ�Q?span style="color: #ff0000">table="user_server"
指定User表与中间表关联的外键�Q?span style="color: #800000">key column="user_id"
指定集合中的对象�c�d��为：many-to-many class="paul.com.Server"
指定中间表与Server兌��的外键：column="server_id"
指定如果同时新增、修攏V��删除关联的Room和User对象�Ӟ��是否需要HIBERNATE执行两次操作�Q?span style="color: #ff0000">cascade="save-update"

如此配置后，��大量减��SQL语句的撰写�?br />

paulwong 2009-05-01 11:57 发表评论

用Hibernate实现领域对象的自定义字段

paulwong — Wed, 23 Jan 2008 03:57:00 GMT
     摘要: ��D�� 在开发企业��业务应用�Q�企业规模）�Ӟ��客户往往要求在不修改�pȝ��源代码的情况下对应用对象模型的扩展性提供支持。利用可扩展域模型可以实现新功能的开发，而不需要额外的�_�֊�和成�? 应用的��用周期将被�g长；外部因素改变�Ӟ��pȝ��工作��也可以随之被修改；已经被部�|�的应用可以�?#8220;讑֮�”�Q��其符合企业的特定情况�? 完成以上功能...  阅读全文

paulwong 2008-01-23 11:57 发表评论

亚洲精品永久在线观看,亚洲日产乱码一二三区别 ,亚洲综合自拍成人

JPA概要

1 JPA概述

2 实体生命周期

3.1 基本映射

3.2 ID生成�{�略

3.3 兌���关系

3.4 �l�承关系

4 事�g及监�?/h2>通过在实体的�Ҏ��上标注@PrePersist�Q�@PostPersist�{�声明即可在事�g发生时触发这些方法�?/p>

5 Query Language 查询语言

5.1 使用参数

5.2 命名查询

5.3 排序

5.4 聚合查询

5.6 更多

6 事务���理

Hibernate Tools

Hibernate Tools其它参考资�?/h3>Hibernate Tools Reference Guide [官方文档] Hibernate Tools Eclipse Plugins [官方文档�Q�Hibernate Tools Eclipse插�g]paulwong 2012-06-10 10:21 发表评论

Using an Example of Sharding with Hibernate

HIBERNATE SHARD

Hibernate Generic D.A.O. Framework

The motivation behind the framework

Why might you consider looking into this framework?

More Information

Questions and Comments

Code Examples

Creating DAOs for individual model classes:

The following methods (and several more) are now available on ProjectDAO

A GeneralDAO is also provided with DAO methods for any entity:

Search DTO usage examples

Nested properties are also fully supported...

JPA使用memcached�?�U�缓存的配置

Hibernate 的session.createCriteria用法

HIBERNATE中的对象设计

用Hibernate实现领域对象的自定义字段

3.3 兌��关系

4 事�g及监�?/h2>
通过在实体的�Ҏ��上标注@PrePersist�Q�@PostPersist�{�声明即可在事�g发生时触发这些方法�?/p>

6 事务��理

Hibernate Tools其它参考资�?/h3>Hibernate Tools Reference Guide [官方文档]
Hibernate Tools Eclipse Plugins [官方文档�Q�Hibernate Tools Eclipse插�g]

paulwong 2012-06-10 10:21 发表评论