jpa与hibernate

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1：新建一个Maven工程，并引入相应的依赖

<groupId>org.apache.openjpa</groupId>

<artifactId>openjpa-all</artifactId>

</dependency>

<groupId>com.driver</groupId>

<artifactId>sqlserver</artifactId>

</dependency>

2：新建一个jpa的配置文件。persistence.xml

位置

标准java工程：src/META-INF/

Maven工程：src/main/resources/META-INF/persistence.xml

<?xmlversion="1.0"encoding="UTF-8"?>

<persistencexmlns="http://java.sun.com/xml/ns/persistence"

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"version="2.0">

<persistence-unitname="FirstJpa"

transaction-type="RESOURCE_LOCAL">

org.apache.openjpa.persistence.PersistenceProviderImpl

</provider>

<class>com.jpa.entity.UserBean</class>

<propertyname="javax.persistence.jdbc.driver"

value="com.microsoft.sqlserver.jdbc.SQLServerDriver"/>

<propertyname="javax.persistence.jdbc.url"

value="jdbc:sqlserver://localhost:1433;DatabaseName=java1411;SelectMethod=cursor;"/>

<propertyname="javax.persistence.jdbc.user"value="sa"/>

<propertyname="javax.persistence.jdbc.password"value=""/>

</properties>

</persistence-unit>

</persistence>

3：新建一个实体对象

UserBean.java

4：将实体对象配置到persistence.xml中。

<class>com.jpa.entity.UserBean</class>

5：JPA中的标准接口

1:EntityManagerFactory(SessionFactory):

javax.persistence.EntityManagerFactory类是创建EntityManager的工厂类。

2:EntityManager:(Session)

javax.persistence.EntityManager是应用中主要使用的接口，它主要用于管理持久对象，也用于创建Query接口。

3:Query:javax.persistence.Query(Query接口)

接口用于持久对象的查询。它支持JavaPersistence Query Language (JPQL) ---->HQL

和Structured Query Language (SQL)。

4:EntityTransaction:EntityTransaction 用于封装事务， (Transaction)

javax.persistence.EntityTransaction和EntityManager之间是一对一的关系

5：Entity。Entity用于封装持久对象。（实体对象）

6:Persistence:javax.persistence.Persistence类包含静态方法用于获得EntityManagerFactory对象。

7:PersistenceException:JPA异常体系的根是PersistenceException，

它继承于RuntimeException。OpenJPA中抛出的异常都实现了

org.apache.openjpa.util.ExceptionInfo接口，用于提供额外的信息。

6：编写JPa的工具类。JpaUtil

import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.Persistence;

public class JpaUtil {

private static final EntityManagerFactory emf;
private static final ThreadLocal<EntityManager> threadLocal;

static {
emf = Persistence.createEntityManagerFactory("FirstJpa");
threadLocal = new ThreadLocal<EntityManager>();
}

public static EntityManager getEntityManager() {
EntityManager manager = threadLocal.get();
if (manager == null || !manager.isOpen()) {
manager = emf.createEntityManager();
threadLocal.set(manager);
}
return manager;
}

public static void closeEntityManager() {
EntityManager em = threadLocal.get();
threadLocal.set(null);
if (em != null)
em.close();
}
}

7：测试

Jpa与Hibernate中方法的区别

JPA Hibernate

persist save

getReference load

find get

merge update

remove delete

查询

query.getResultList query.list();

query.getSingleResult query.uniqueResult();

分页

query.setFirstResult(2);

query.setMaxResults(2);

8：将OpenJpa切换为Hibernate

0：Hibernate的persistence.xml的配置

<?xml version="1.0"encoding="UTF-8"?>

<persistencexmlns="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-unitname="FirstJpa"

transaction-type="RESOURCE_LOCAL">

org.hibernate.jpa.HibernatePersistenceProvider

</provider>

<class>com.jpa.entity.UserBean</class>

<propertyname="javax.persistence.jdbc.driver"

value="com.microsoft.sqlserver.jdbc.SQLServerDriver"/>

<propertyname="javax.persistence.jdbc.url"

value="jdbc:sqlserver://localhost:1433;DatabaseName=java1411;SelectMethod=cursor;"/>

<propertyname="javax.persistence.jdbc.user" value="sa" />

<propertyname="javax.persistence.jdbc.password" value="" />

</properties>

</persistence-unit>

</persistence>

OpenJpa的persistence.xml的配置

<?xml version="1.0"encoding="UTF-8"?>

<persistencexmlns="http://java.sun.com/xml/ns/persistence"

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"version="2.0">

<persistence-unitname="FirstJpa"

transaction-type="RESOURCE_LOCAL">

org.apache.openjpa.persistence.PersistenceProviderImpl

</provider>

<class>com.jpa.entity.UserBean</class>

<class>com.jpa.entity.ScoreBean</class>

<class>com.jpa.entity.ScoreID</class>

<class>com.jpa.entity.many_to_one.GroupBean</class>

<class>com.jpa.entity.many_to_one.GroupUser</class>

<class>com.jpa.entity.one_to_many.ClassesBean</class>

<class>com.jpa.entity.one_to_many.StudentBean</class>

<class>com.jpa.entity.one_to_one.PersonBean</class>

<class>com.jpa.entity.one_to_one.CardBean</class>

<propertyname="javax.persistence.jdbc.driver"

value="com.microsoft.sqlserver.jdbc.SQLServerDriver"/>

<propertyname="javax.persistence.jdbc.url"

value="jdbc:sqlserver://localhost:1433;DatabaseName=java1411;SelectMethod=cursor;"/>

<propertyname="javax.persistence.jdbc.user" value="sa" />

<propertyname="javax.persistence.jdbc.password" value="" />

<propertyname="openjpa.jdbc.SynchronizeMappings"

value="buildSchema(ForeignKeys=true)"/>

<propertyname="openjpa.Log" value="SQL=TRACE" />

<propertyname="openjpa.ConnectionFactoryProperties"

value="PrettyPrint=true,PrettyPrintLineLength=72" />

</properties>

</persistence-unit>

</persistence>

工程中不能同时引入OpenJPA的jar与Hibernate的jar包。

9：复合主键

与Hibernate不同的注意点：

1：persistence.xml中要加入2个实体对象（ID与实体对象）

2：ID实体对象要实现hashCode与equals（）方法。

<class>com.jpa.entity.ScoreBean</class>

<class>com.jpa.entity.ScoreID</class>

10：多表操作

Many_To_One

One_To_Many

尽量使用List，不用SET。SET的排序在JPA中是无序的。

One_To_One

Many_To_Many

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