say i have Library, Book, and Page classes. a Library has many Books, and a
Book has many Pages. A Library's ID is it's name (simple). A Book's ID is a
composite of it's name and it's owning Library's name (bidirectional
relationship). A Page's ID is a composite of it's number and it's owning Book's
ID, a BookID.
so, the PageId class starts like:
public class PageId implements Serializable {
private int number;
private BookId book;
the error i'm getting is at runtime ...
<4|true|0.9.6-incubating> org.apache.openjpa.persistence.ArgumentException:
Field "com.mycompany.book.Book.pages" declares "com.mycompany.book.Page.book"
as its mapped-by field, but this field is not a direct relation.
first, is what i'm trying to do even valid? i suspect it is not, and the
problem is that the fields of the ID class must be "simple" types (i believe
the spec demands that). although, the error message is a little confusing so i
am not sure.
it occurs to me that another way to achieve this would be to add bookName and
libraryName fields to the Page class, and add a @PrePersist method that
populates them by calling book.getName() and book.getLibrary().getName(). but
again this is messy because that data is already in the table because of the
bidirectional relationship between the objects.
as always, i'm open to "what are you an idiot?" responses if i am just going
about trying to define the Library, Book, Page relationship in an obtuse manner.
classes attached.
---------------------------------
The fish are biting.
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import java.io.Serializable;
import java.util.HashSet;
import java.util.Set;
import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.IdClass;
import javax.persistence.ManyToOne;
import javax.persistence.OneToMany;
import javax.xml.bind.annotation.XmlAttribute;
import javax.xml.bind.annotation.XmlElement;
@IdClass(com.mycompany.book.BookId.class)
@Entity
public class Book implements Serializable {
@Id
@Column(
name="BOOK_NAME",
nullable = false
)
@XmlAttribute (required = true)
private String name;
@OneToMany(
cascade = CascadeType.ALL,
mappedBy = "book"
)
@XmlElement (name = "page")
private Set<Page> pages = new HashSet<Page>();
@Id
@Column(
nullable = false
)
@ManyToOne (
cascade = CascadeType.ALL
)
private Library library;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Page getPage(int n) {
for (Page p: pages) {
if (p.getNumber() == n) {
return p;
}
}
return null;
}
public void putPage(Page p) {
p.setBook(this);
pages.add(p);
}
public boolean equals(Object o) {
if (!(o instanceof Book)) {
return false;
}
Book other = (Book)o;
if (!getName().equals(other.getName())) {
return false;
}
return true;
}
public int hashCode() {
return getName().hashCode();
}
public Library getLibrary() {
return library;
}
public void setLibrary(Library library) {
this.library = library;
}
}
package com.mycompany.book;
import java.io.Serializable;
import javax.xml.bind.annotation.XmlTransient;
@XmlTransient
public class BookId implements Serializable {
private String name;
private String library;
public boolean equals(Object o) {
if (!(o instanceof BookId)) {
return false;
}
BookId other = (BookId)o;
if (!(getName().equals(other.getName()))) {
return false;
}
if (!getLibrary().equals(other.getLibrary())) {
return false;
}
return true;
}
public int hashCode() {
return getName().hashCode() * getLibrary().hashCode();
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getLibrary() {
return library;
}
public void setLibrary(String library) {
this.library = library;
}
}
package com.mycompany.book;
import java.io.Serializable;
import java.util.HashSet;
import java.util.Set;
import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.OneToMany;
import javax.xml.bind.annotation.XmlAttribute;
import javax.xml.bind.annotation.XmlElement;
import javax.xml.bind.annotation.XmlRootElement;
@Entity
@XmlRootElement
public class Library implements Serializable {
@Id
@Column(
name="LIBRARY_NAME",
nullable = false
)
@XmlAttribute (name = "name", required = true)
private String name;
@OneToMany(
cascade = CascadeType.ALL,
mappedBy = "library"
)
@XmlElement (name = "book")
private Set<Book> books = new HashSet<Book>();
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Book getBook(String name) {
for (Book b: books) {
if (b.getName().equals(name)) {
return b;
}
}
return null;
}
public void putBook(Book book) {
book.setLibrary(this);
books.add(book);
}
public boolean equals(Object o) {
if (!(o instanceof Library)) {
return false;
}
Library other = (Library)o;
if (!getName().equals(other.getName())) {
return false;
}
return true;
}
public int hashCode() {
return getName().hashCode();
}
}
package com.mycompany.book;
import java.io.Serializable;
import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.IdClass;
import javax.persistence.ManyToOne;
import javax.xml.bind.annotation.XmlAttribute;
@IdClass(com.mycompany.book.PageId.class)
@Entity
public class Page implements Serializable {
@Id
@Column(
name="PAGE_NUMBER",
nullable = false
)
@XmlAttribute
private int number;
@Id
@Column(
nullable = false
)
@ManyToOne (
cascade = CascadeType.ALL
)
private Book book;
public int getNumber() {
return number;
}
public void setNumber(int number) {
this.number = number;
}
public Book getBook() {
return book;
}
public void setBook(Book book) {
this.book = book;
}
}
package com.mycompany.book;
import java.io.Serializable;
import javax.xml.bind.annotation.XmlTransient;
@XmlTransient
public class PageId implements Serializable {
private int number;
private BookId book;
public int getNumber() {
return number;
}
public void setNumber(int number) {
this.number = number;
}
public boolean equals(Object o) {
if (!(o instanceof PageId)) {
return false;
}
PageId other = (PageId)o;
if (!(getNumber() == other.getNumber())) {
return false;
}
if (!getBook().equals(other.getBook())) {
return false;
}
return true;
}
public int hashCode() {
return number * getBook().hashCode();
}
public BookId getBook() {
return book;
}
public void setBook(BookId book) {
this.book = book;
}
}
