Part 1-JDO/JPAは双方向、有主、一対多(one-to-many)の関係を確立する

こんにちは、第1部の「JDO/JPA Snippets That Work」へようこそ!
双方向の有主の一対の多関係を確立する
図書カタログアプリケーションを構築している場合、本と章をモデリングしたいとします.本には章が含まれており、章は本とは独立して存在しません.そのため、本を削除すると、彼の章も自動的に削除されます.また、各章のインスタンスは、この章を持つ本への参照を指していると思います.これはまさに双方向で、主がいて、一対多の関係に聞こえます.
まず私たちは私たちのモデルを構築し、その後、2つの章を持つ本をモデルにします.
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 
} 

2つの章を持つ本を作成しましょう(「em」というEntityManagerを作成して閉じる人がいると仮定します)

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 
} 

2つの章を持つ本を作成しましょう(「em」というEntityManagerを作成して閉じる人がいると仮定します)

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(); 
    } 
}

英語原文:
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(); 
    }
} 

転載先:
http://groups.google.com/group/google-appengine-java/browse_thread/thread/54c83dc6242fd633
说明:上の中国语の翻訳は私が自分で理解できる方法で翻訳したもので、逐字翻訳ではなく、自分の参考にするだけで、あまり正确ではありません.