Java 双向多对一映射

我不熟悉JAVA和JPA，我在谷歌上搜索了解决方案，但没用。我找到了很多例子，但它们在我的场景中不起作用。 我想映射以下两个表：

书架桌

CREATE TABLE "SOA2"."BOOKSHELF"  (  
"BOOKSHELF_ID" NUMBER(19,0) NOT NULL ENABLE, 
"NAME_TXT" VARCHAR2(255 CHAR), 
 PRIMARY KEY ("BOOKSHELF_ID") USING INDEX PCTFREE 10 INITRANS 2 
 MAXTRANS 255 NOCOMPRESS LOGGING
 TABLESPACE "SOA2"  ENABLE
 ) SEGMENT CREATION DEFERRED PCTFREE 10 PCTUSED 40 INITRANS 1 
 MAXTRANS 255 NOCOMPRESS LOGGING TABLESPACE "SOA2" ;

CREATE TABLE "SOA2"."BOOK" (    
"BOOK_IX" NUMBER(19,0) NOT NULL ENABLE, 
"BOOKSHELF_ID" NUMBER(19,0) NOT NULL ENABLE, 
"NAME_TXT" VARCHAR2(255 CHAR), 
 PRIMARY KEY ("BOOK_IX", "BOOKSHELF_ID") USING INDEX PCTFREE 10 INITRANS 2 
 MAXTRANS 255 NOCOMPRESS LOGGING   TABLESPACE "SOA2"  ENABLE, CONSTRAINT "FK_RJWHY4FC" 
 FOREIGN KEY ("BOOKSHELF_ID")
 REFERENCES "SOA2"."BOOKSHELF" ("BOOKSHELF_ID") ENABLE) 
 SEGMENT CREATION DEFERRED PCTFREE 10 PCTUSED 40 INITRANS 1 
  MAXTRANS 255 NOCOMPRESS LOGGING  TABLESPACE "SOA2" ;

及

书桌

CREATE TABLE "SOA2"."BOOKSHELF"  (  
"BOOKSHELF_ID" NUMBER(19,0) NOT NULL ENABLE, 
"NAME_TXT" VARCHAR2(255 CHAR), 
 PRIMARY KEY ("BOOKSHELF_ID") USING INDEX PCTFREE 10 INITRANS 2 
 MAXTRANS 255 NOCOMPRESS LOGGING
 TABLESPACE "SOA2"  ENABLE
 ) SEGMENT CREATION DEFERRED PCTFREE 10 PCTUSED 40 INITRANS 1 
 MAXTRANS 255 NOCOMPRESS LOGGING TABLESPACE "SOA2" ;

CREATE TABLE "SOA2"."BOOK" (    
"BOOK_IX" NUMBER(19,0) NOT NULL ENABLE, 
"BOOKSHELF_ID" NUMBER(19,0) NOT NULL ENABLE, 
"NAME_TXT" VARCHAR2(255 CHAR), 
 PRIMARY KEY ("BOOK_IX", "BOOKSHELF_ID") USING INDEX PCTFREE 10 INITRANS 2 
 MAXTRANS 255 NOCOMPRESS LOGGING   TABLESPACE "SOA2"  ENABLE, CONSTRAINT "FK_RJWHY4FC" 
 FOREIGN KEY ("BOOKSHELF_ID")
 REFERENCES "SOA2"."BOOKSHELF" ("BOOKSHELF_ID") ENABLE) 
 SEGMENT CREATION DEFERRED PCTFREE 10 PCTUSED 40 INITRANS 1 
  MAXTRANS 255 NOCOMPRESS LOGGING  TABLESPACE "SOA2" ;

为便于理解，其结构如下所示

及 在所有的搜索之后，我使用了Eclipse“JPA Entities from Tables”工具。 它为我生成了以下类：

Bookshelf.java

@Entity
@Table(name="BOOKSHELF")
public class Bookshelf implements Serializable {
    @Id
    @Column(name="BOOKSHELF_ID", unique=true)
    private long bookshelfId;
    @Column(name="NAME_TXT")
    private String nameTxt;
    //bi-directional many-to-one association to Book
    @OneToMany(mappedBy="bookshelf", cascade={CascadeType.ALL})
    private List<Book> books;
    public List<Book> getBooks() {
        return this.books;
    }
    public void setBooks(List<Book> books) {
        this.books = books;
    }
//Code removed for the sake of brevity
}

    @Entity
    @Table(name="BOOK")
    public class Book implements Serializable {
        @EmbeddedId
        private BookPK id;
        @Column(name="NAME_TXT", length=255)
        private String nameTxt;
        //bi-directional many-to-one association to Bookshelf
        @ManyToOne(cascade={CascadeType.ALL})
        @JoinColumn(name="BOOKSHELF_ID", nullable=false, insertable=false, updatable=false)
        private Bookshelf bookshelf;
    //Code removed for the sake of brevity
    }

@Embeddable
public class BookPK implements Serializable {
@Column(name="BOOK_IX")
private long bookIx;
@Column(name="BOOKSHELF_ID", insertable=false, updatable=false, unique=true, nullable=false)
private long bookshelfId;
public BookPK(long bkShlfId, long bkId) {
    this.bookshelfId = bkShlfId;
    this.bookIx = bkId;
}
//Code removed for the sake of brevity 

        //Physics Bookshelf
        Bookshelf physicsShelf = new Bookshelf();
        physicsShelf.setNameTxt("Physics");
        physicsShelf.setBookshelfId(500);
        //Add Books
        Book book1 = new Book();
        book1.setNameTxt("God and the Physics");
        book1.setId(new BookPK(500, 600));

        Book book2 = new Book();
        book2.setNameTxt("Hyperspace");
        //if I pass 500 as first param in below constructor 
        //Changing 500 to 501 solves the issue
        book2.setId(new BookPK(500, 600)); //javax.persistence.EntityExistsException: A different object with the same identifier value was already associated with the session : [books.Book#books.BookPK@8a6d]

        //Add Books into list
        List<Book> bookList = new ArrayList<Book>();
        bookList.add(book1);
        //Error: Following error appears if I uncomment the following line
        bookList.add(book2); //Caused by: java.sql.SQLIntegrityConstraintViolationException: ORA-02291: integrity constraint (SOA2.FK_RJ) violated - parent key not found
        //Set Books
        physicsShelf.setBooks(bookList);
        EntityTransaction transaction = entitymanager.getTransaction();
        transaction.begin();
        entitymanager.persist(physicsShelf);
        transaction.commit();

BookPK.java

@Entity
@Table(name="BOOKSHELF")
public class Bookshelf implements Serializable {
    @Id
    @Column(name="BOOKSHELF_ID", unique=true)
    private long bookshelfId;
    @Column(name="NAME_TXT")
    private String nameTxt;
    //bi-directional many-to-one association to Book
    @OneToMany(mappedBy="bookshelf", cascade={CascadeType.ALL})
    private List<Book> books;
    public List<Book> getBooks() {
        return this.books;
    }
    public void setBooks(List<Book> books) {
        this.books = books;
    }
//Code removed for the sake of brevity
}

    @Entity
    @Table(name="BOOK")
    public class Book implements Serializable {
        @EmbeddedId
        private BookPK id;
        @Column(name="NAME_TXT", length=255)
        private String nameTxt;
        //bi-directional many-to-one association to Bookshelf
        @ManyToOne(cascade={CascadeType.ALL})
        @JoinColumn(name="BOOKSHELF_ID", nullable=false, insertable=false, updatable=false)
        private Bookshelf bookshelf;
    //Code removed for the sake of brevity
    }

@Embeddable
public class BookPK implements Serializable {
@Column(name="BOOK_IX")
private long bookIx;
@Column(name="BOOKSHELF_ID", insertable=false, updatable=false, unique=true, nullable=false)
private long bookshelfId;
public BookPK(long bkShlfId, long bkId) {
    this.bookshelfId = bkShlfId;
    this.bookIx = bkId;
}
//Code removed for the sake of brevity 

        //Physics Bookshelf
        Bookshelf physicsShelf = new Bookshelf();
        physicsShelf.setNameTxt("Physics");
        physicsShelf.setBookshelfId(500);
        //Add Books
        Book book1 = new Book();
        book1.setNameTxt("God and the Physics");
        book1.setId(new BookPK(500, 600));

        Book book2 = new Book();
        book2.setNameTxt("Hyperspace");
        //if I pass 500 as first param in below constructor 
        //Changing 500 to 501 solves the issue
        book2.setId(new BookPK(500, 600)); //javax.persistence.EntityExistsException: A different object with the same identifier value was already associated with the session : [books.Book#books.BookPK@8a6d]

        //Add Books into list
        List<Book> bookList = new ArrayList<Book>();
        bookList.add(book1);
        //Error: Following error appears if I uncomment the following line
        bookList.add(book2); //Caused by: java.sql.SQLIntegrityConstraintViolationException: ORA-02291: integrity constraint (SOA2.FK_RJ) violated - parent key not found
        //Set Books
        physicsShelf.setBooks(bookList);
        EntityTransaction transaction = entitymanager.getTransaction();
        transaction.begin();
        entitymanager.persist(physicsShelf);
        transaction.commit();

}

我以如下方式进行测试：Test.java

@Entity
@Table(name="BOOKSHELF")
public class Bookshelf implements Serializable {
    @Id
    @Column(name="BOOKSHELF_ID", unique=true)
    private long bookshelfId;
    @Column(name="NAME_TXT")
    private String nameTxt;
    //bi-directional many-to-one association to Book
    @OneToMany(mappedBy="bookshelf", cascade={CascadeType.ALL})
    private List<Book> books;
    public List<Book> getBooks() {
        return this.books;
    }
    public void setBooks(List<Book> books) {
        this.books = books;
    }
//Code removed for the sake of brevity
}

    @Entity
    @Table(name="BOOK")
    public class Book implements Serializable {
        @EmbeddedId
        private BookPK id;
        @Column(name="NAME_TXT", length=255)
        private String nameTxt;
        //bi-directional many-to-one association to Bookshelf
        @ManyToOne(cascade={CascadeType.ALL})
        @JoinColumn(name="BOOKSHELF_ID", nullable=false, insertable=false, updatable=false)
        private Bookshelf bookshelf;
    //Code removed for the sake of brevity
    }

@Embeddable
public class BookPK implements Serializable {
@Column(name="BOOK_IX")
private long bookIx;
@Column(name="BOOKSHELF_ID", insertable=false, updatable=false, unique=true, nullable=false)
private long bookshelfId;
public BookPK(long bkShlfId, long bkId) {
    this.bookshelfId = bkShlfId;
    this.bookIx = bkId;
}
//Code removed for the sake of brevity 

        //Physics Bookshelf
        Bookshelf physicsShelf = new Bookshelf();
        physicsShelf.setNameTxt("Physics");
        physicsShelf.setBookshelfId(500);
        //Add Books
        Book book1 = new Book();
        book1.setNameTxt("God and the Physics");
        book1.setId(new BookPK(500, 600));

        Book book2 = new Book();
        book2.setNameTxt("Hyperspace");
        //if I pass 500 as first param in below constructor 
        //Changing 500 to 501 solves the issue
        book2.setId(new BookPK(500, 600)); //javax.persistence.EntityExistsException: A different object with the same identifier value was already associated with the session : [books.Book#books.BookPK@8a6d]

        //Add Books into list
        List<Book> bookList = new ArrayList<Book>();
        bookList.add(book1);
        //Error: Following error appears if I uncomment the following line
        bookList.add(book2); //Caused by: java.sql.SQLIntegrityConstraintViolationException: ORA-02291: integrity constraint (SOA2.FK_RJ) violated - parent key not found
        //Set Books
        physicsShelf.setBooks(bookList);
        EntityTransaction transaction = entitymanager.getTransaction();
        transaction.begin();
        entitymanager.persist(physicsShelf);
        transaction.commit();

//物理书架
Bookshelf physicsShelf=新书架（）；
physicshelf.setNameTxt（“Physics”）；
physicsShelf.setBookshelfId（500）；
//添加书籍
Book book1=新书（）；
book1.setNameTxt（“上帝与物理学”）；
book1.setId（新BookPK（500600））；
Book book2=新书（）；
book2.setNameTxt（“超空间”）；
//如果我通过500作为下面构造函数中的第一个参数
//将500更改为501解决了这个问题
book2.setId（新BookPK（500600））//javax.persistence.EntityExistsException:具有相同标识符值的不同对象已与会话：[books.Book#books]关联。BookPK@8a6d]
//将书籍添加到列表中
List bookList=newarraylist（）；
图书目录。添加（第1册）；
//错误：如果我取消注释以下行，将出现以下错误
增加（第2册）//原因：java.sql.SQLIntegrityConstraintViolationException:ORA-02291:违反完整性约束（SOA2.FK_RJ）-未找到父密钥
//订书
physicsShelf.setBooks（书目）；
EntityTransaction=entitymanager.getTransaction（）；
transaction.begin（）；
entitymanager.persist（physicsShelf）；
commit（）；

physicsShelf只成功插入了一本书，如果我在图书列表中插入第二本书，它会给出Test.java注释中描述的错误

请引导我

我做错了什么以及如何纠正它。我真的被卡住了

有没有办法通过注释另外两个类来摆脱BookPK.java类

我无法更改数据库 我正在使用oracle 11g和JPA 2.1

任何帮助都将不胜感激

---

关于

id应该是唯一的，但在您的情况下，您将book1和book2的id都设置为Book（500600）

因此，当您尝试添加

book2.setId（newBookPK（500600））时它正在抱怨它已经存在

试一试

编辑：第二个问题

我想你可以。在书中尝试替换实体

@EmbeddedId
private BookPK id;

与

book2的bookId是否应与book1的bookId不同？在上面的代码中，两者的id似乎与600相同？谢谢你的回答。非常感谢。我想我已经试过了。成功了。很抱歉这个愚蠢的问题。谢谢你的回答。我的第二个问题呢？