你好,欢迎来到第一部分的"JDO/JPA Snippets That Work"!
建立一个双向的有主的一对多关系
假设你正在建立一个图书目录应用程序,你想为书和章节建模:书本包含章节,章节不能独立于书本存在,所以如果你删除一本书,他的章节也会跟着自动删除。同时你想每一个章节的实例都一个指向拥有这个章节的书本的引用。听起来,这正是双向的,有主的,一对对多的关系。
首先我们将建立我们的模型,之后我将示范建立一本带有2个章节的书。
JPA:
@Entity
public class Book {
@Id
@GeneratedValue(strategy=GenerationType.IDENTITY)
private Key id;
private String title;
@OneToMany(mappedBy = "book", cascade = CascadeType.ALL)
private List<Chapter> chapters = new ArrayList<Chapter>();
// getters and setters
}
@Entity
public class Chapter {
@Id
@GeneratedValue(strategy=GenerationType.IDENTITY)
private Key id;
private String title;
private int numPages;
@ManyToOne(fetch = FetchType.LAZY)
private Book book;
// getters and setters
}
现在让我们建立一个带有两个章节的书本(我们假设有人已经为我们建立和关闭一个叫'em'的EntityManager)
Book b = new Book();
b.setTitle("JPA 4eva");
Chapter c1 = new Chapter();
c1.setTitle("Intro");
c1.setNumPages(10);
b.getChapters().add(c1);
Chapter c2 = new Chapter();
c2.setTitle("Configuration");
c2.setNumPages(9);
b.getChapters().add(c2);
em.getTransaction().begin();
try {
em.persist(b);
em.getTransaction().commit();
} finally {
if (em.getTransaction().isActive()) {
em.getTransaction().rollback();
}
}
JDO:
@PersistenceCapable(identityType = IdentityType.APPLICATION, detachable =
"true")
public class Book {
@PrimaryKey
@Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
private Key id;
private String title;
@Persistent(mappedBy = "book")
@Element(dependent = "true")
private List<Chapter> chapters = new ArrayList<Chapter>();
// getters and setters
}
@PersistenceCapable(identityType = IdentityType.APPLICATION, detachable =
"true")
public class Chapter {
@PrimaryKey
@Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
private Key id;
private String title;
private int numPages;
@Persistent
private Book book;
// getters and setters
}
现在让我们建立一个带有两个章节的书本(我们假设有人已经为我们建立和关闭一个叫'em'的EntityManager)
Book b = new Book();
b.setTitle("JDO 4eva");
Chapter c1 = new Chapter();
c1.setTitle("Intro");
c1.setNumPages(10);
b.getChapters().add(c1);
Chapter c2 = new Chapter();
c2.setTitle("Configuration");
c2.setNumPages(9);
b.getChapters().add(c2);
pm.currentTransaction().begin();
try {
pm.makePersistent(b);
pm.currentTransaction().commit();
} finally {
if (pm.currentTransaction().isActive()) {
pm.currentTransaction().rollback();
}
}
英语原文:
Hello hello and welcome to the very first installment of JDO/JPA Snippets
That Work!
Creating A Bidrectional Owned One-To-Many
Suppose you're building a book catalog application and you want to model
books and chapters. Books contain chapters. A chapter cannot exist without
a book, so if you delete a book you want its chapters automatically deleted
along with it. You also want to each chapter to have a reference to the
book that owns it. Sounds like a bidrectional, owned, one-to-many
relationship is just the thing. First we'll set up our model objects and
then we'll add some code to create a Book with 2 Chapters.
JPA:
@Entity
public class Book {
@Id
@GeneratedValue(strategy=GenerationType.IDENTITY)
private Key id;
private String title;
@OneToMany(mappedBy = "book", cascade = CascadeType.ALL)
private List<Chapter> chapters = new ArrayList<Chapter>();
// getters and setters
}
@Entity
public class Chapter {
@Id
@GeneratedValue(strategy=GenerationType.IDENTITY)
private Key id;
private String title;
private int numPages;
@ManyToOne(fetch = FetchType.LAZY)
private Book book;
// getters and setters
}
Now let's create a book with two chapters (we'll assume someone else is
creating and closing an EntityManager named 'em' for us):
Book b = new Book();
b.setTitle("JPA 4eva");
Chapter c1 = new Chapter();
c1.setTitle("Intro");
c1.setNumPages(10);
b.getChapters().add(c1);
Chapter c2 = new Chapter();
c2.setTitle("Configuration");
c2.setNumPages(9);
b.getChapters().add(c2);
em.getTransaction().begin();
try {
em.persist(b);
em.getTransaction().commit();
} finally {
if (em.getTransaction().isActive()) {
em.getTransaction().rollback();
}
}
JDO:
@PersistenceCapable(identityType = IdentityType.APPLICATION, detachable =
"true")
public class Book {
@PrimaryKey
@Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
private Key id;
private String title;
@Persistent(mappedBy = "book")
@Element(dependent = "true")
private List<Chapter> chapters = new ArrayList<Chapter>();
// getters and setters
}
@PersistenceCapable(identityType = IdentityType.APPLICATION, detachable =
"true")
public class Chapter {
@PrimaryKey
@Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
private Key id;
private String title;
private int numPages;
@Persistent
private Book book;
// getters and setters
}
Now let's create a book with two chapters (we'll assume someone else is
creating and closing a PersistenceManager named 'pm' for us):
Book b = new Book();
b.setTitle("JDO 4eva");
Chapter c1 = new Chapter();
c1.setTitle("Intro");
c1.setNumPages(10);
b.getChapters().add(c1);
Chapter c2 = new Chapter();
c2.setTitle("Configuration");
c2.setNumPages(9);
b.getChapters().add(c2);
pm.currentTransaction().begin();
try {
pm.makePersistent(b);
pm.currentTransaction().commit();
} finally {
if (pm.currentTransaction().isActive()) {
pm.currentTransaction().rollback();
}
}
转载自:
http://groups.google.com/group/google-appengine-java/browse_thread/thread/54c83dc6242fd633
说明:上面的中文翻译是我用自己能理解的方式翻译出来的,并不是逐字翻译,只作为自己参考用,并不十分精确。
分享到:
相关推荐
赠送jar包:datanucleus-api-jdo-3.2.6.jar; 赠送原API文档:datanucleus-api-jdo-3.2.6-javadoc.jar; 赠送源代码:datanucleus-api-jdo-3.2.6-sources.jar; 赠送Maven依赖信息文件:datanucleus-api-jdo-3.2.6....
赠送jar包:datanucleus-api-jdo-4.2.1.jar; 赠送原API文档:datanucleus-api-jdo-4.2.1-javadoc.jar; 赠送源代码:datanucleus-api-jdo-4.2.1-sources.jar; 赠送Maven依赖信息文件:datanucleus-api-jdo-4.2.1....
datanucleus-api-jdo-3.2.6.jar )
/xscjManager/WebContent/WEB-INF/lib/spring-jdo.jar /xscjManager/WebContent/WEB-INF/lib/spring-jms.jar /xscjManager/WebContent/WEB-INF/lib/spring-jmx.jar /xscjManager/WebContent/WEB-INF/lib/spring-jpa....
对JDO 1.0/2.0的支持。外部依赖spring-jdbc, JDO API, (spring-web)。
Java Persistence API (JPA) 是Java平台上的一个标准,用于管理和持久化Java对象到关系数据库。JPA提供了一种模型化的面向对象的方式来处理数据库操作,使得开发者无需编写大量SQL代码即可实现数据的增删改查。 **...
Java Data Objects(JDO)是Java平台上的一个标准接口,它提供了一种透明的对象/关系映射机制,使得开发者可以以面向对象的方式操作数据库,而无需直接编写SQL语句。JDO通过API将Java对象与数据库中的记录进行映射,...
赠送jar包:javax.jdo-3.2.0-m3.jar; 赠送原API文档:javax.jdo-3.2.0-m3-javadoc.jar; 赠送源代码:javax.jdo-3.2.0-m3-sources.jar; 赠送Maven依赖信息文件:javax.jdo-3.2.0-m3.pom; 包含翻译后的API文档:...
JDO2-API-2.3-EC是Java对象持久化的一个重要实现,它定义了数据存储和检索的接口,使得对象可以被透明地存储到关系数据库、NoSQL数据库甚至是对象数据库中。此版本引入了若干改进和新特性,以提升性能和可扩展性,...
jdo2-api jdo2-api jdo2-api jdo2-api
JavaEE源代码 spring-jdoJavaEE源代码 ...jdoJavaEE源代码 spring-jdoJavaEE源代码 spring-jdoJavaEE源代码 spring-jdoJavaEE源代码 spring-jdoJavaEE源代码 spring-jdoJavaEE源代码 spring-jdoJavaEE源代码 spring-jdo
Querydsl 是一个强大的Java查询语言库,它提供了一种类型安全的方式来表达SQL、JDO和JPA查询。在3.3.3版本中,Querydsl 提供了JPA Codegen工具,这是一款代码生成器,能够自动生成基于Querydsl的JPA查询实体类。通过...
DataNucleus是一个开源的对象关系映射(ORM)框架,它允许开发人员将Java对象持久化到各种数据存储。JDO是Java平台上的一个标准接口,它提供了一种方式来透明地访问和管理持久性数据。JCA则是Java EE平台的一部分,...
Querydsl是一个强大的Java查询工具包,它提供了类型安全的查询API,可以用于JPA、SQL、JDO等多种数据访问技术。在Querydsl JPA中,你可以利用Java对象来构建复杂的JPQL(Java Persistence Query Language)查询,...
【标题】"gaedo-google-jdo-0.2.24.zip" 提供的是 Google 的 Java Data Objects (JDO) 库的一个版本,这是一款针对关系数据库的数据持久化框架。Google JDO 允许开发者使用面向对象的方式操作数据库,简化了数据库...
Querydsl是一个用于创建类型安全查询的Java库,它支持JPA、JDO、SQL等多种持久化技术。Querydsl通过代码生成,将查询表达式转化为可读性强的Java对象,避免了字符串拼接造成的潜在错误,提高了代码质量。 三、...
### J2EE持久化选项:JDO、Hibernate与EJB 3.0 #### 概述 在《J2EE Persistence Options - JDO, Hibernate and EJB 3.0》这篇文档中,作者Sridhar Reddy深入探讨了Java 2 Platform, Enterprise Edition (J2EE)环境...
赠送jar包:jdo-api-3.0.1.jar; 赠送原API文档:jdo-api-3.0.1-javadoc.jar; 赠送源代码:jdo-api-3.0.1-sources.jar; 赠送Maven依赖信息文件:jdo-api-3.0.1.pom; 包含翻译后的API文档:jdo-api-3.0.1-javadoc-...
创建一个新的子文件夹docs / api32 / jdo-api-3.2-javadoc 在子文件夹中解压缩javadoc jar 在src / main / asciidoc下编辑javadoc.adoc并创建一个新的“ JDO 3.2 javadoc”部分。 添加两个链接: