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CarlSagan
 Post subject: How to create an identified 1xN relation ?
PostPosted: Thu Jan 14, 2010 5:48 pm 
Newbie

Joined: Thu Jan 14, 2010 5:43 pm
Posts: 8
Hello!

I want to translate this to my classes using Annotations:

Image

How do I do it?



Some code that may help:
Code:
@Entity
public class Book {
    @Id
    private int idBook;
    private String title;
    //getters & setters...
}


@Entity
public class Edition {
    @Id
    private int idEdition;
    private int yearPublished;
    //getters & setters...
}
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kaza7
 Post subject: Re: How to create an identified 1xN relation ?
PostPosted: Thu Jan 14, 2010 6:03 pm 
Newbie

Joined: Mon Jan 11, 2010 11:05 am
Posts: 8
in your class Book, you can add :

@OneToMany(cascade = { CascadeType.ALL })
@JoinColumn(name="Book_idBook")
private Set<Edition> editions;

getter/setter...
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CarlSagan
 Post subject: Re: How to create an identified 1xN relation ?
PostPosted: Thu Jan 14, 2010 6:17 pm 
Newbie

Joined: Thu Jan 14, 2010 5:43 pm
Posts: 8
kaza7 wrote:
in your class Book, you can add :

@OneToMany(cascade = { CascadeType.ALL })
@JoinColumn(name="Book_idBook")
private Set<Edition> editions;

getter/setter...


But that just generates me a non-identified relation (that is, the FK isn't PK also).
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CarlSagan
 Post subject: Re: How to create an identified 1xN relation ?
PostPosted: Wed Jan 20, 2010 5:18 pm 
Newbie

Joined: Thu Jan 14, 2010 5:43 pm
Posts: 8
Wow, no one knows?
I thought it was simple.
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pb00067
 Post subject: Re: How to create an identified 1xN relation ?
PostPosted: Thu Jan 21, 2010 4:20 am 
Expert
Expert

Joined: Tue Jun 16, 2009 3:36 am
Posts: 990
Please explain more in detail what you understand with a identified 1xN relation.
For instance you have a determinate book which has 3 editions.
How many book instances do you want to have in the db?
Just one or 3 (a instance for each edition) ?
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pb00067
 Post subject: Re: How to create an identified 1xN relation ?
PostPosted: Thu Jan 21, 2010 4:43 am 
Expert
Expert

Joined: Tue Jun 16, 2009 3:36 am
Posts: 990
anyway I would suggest you following:
Code:
in your class Book:
@javax.persistence.OneToMany(mappedBy = "bookId")
protected Set<Edition> editions = new java.util.HashSet();


in your class Edition:
Code:
@Id @GeneratedValue
private long id;

@Column
private long edtion;     

@javax.persistence.ManyToOne
protected Book bookId = null;


Otherwise, if you don't want to have the generated id value in class Edition,
you need a composite Id composed by edition + bookid.
In such case you must use the IdClass annotation
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CarlSagan
 Post subject: Re: How to create an identified 1xN relation ?
PostPosted: Thu Jan 21, 2010 8:32 am 
Newbie

Joined: Thu Jan 14, 2010 5:43 pm
Posts: 8
pb00067 wrote:
anyway I would suggest you following:
Code:
in your class Book:
@javax.persistence.OneToMany(mappedBy = "bookId")
protected Set<Edition> editions = new java.util.HashSet();


in your class Edition:
Code:
@Id @GeneratedValue
private long id;

@Column
private long edtion;     

@javax.persistence.ManyToOne
protected Book bookId = null;


Otherwise, if you don't want to have the generated id value in class Edition,
you need a composite Id composed by edition + bookid.
In such case you must use the IdClass annotation


Yes, what I want is to have a composite key (edition + bookId) both being primary keys, exactly as shown in the picture.
Could you show the use of this IdClass annotation in this example, please?

Thanks!
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pb00067
 Post subject: Re: How to create an identified 1xN relation ?
PostPosted: Thu Jan 21, 2010 10:37 am 
Expert
Expert

Joined: Tue Jun 16, 2009 3:36 am
Posts: 990
Which picture do you mean?
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CarlSagan
 Post subject: Re: How to create an identified 1xN relation ?
PostPosted: Thu Jan 21, 2010 12:08 pm 
Newbie

Joined: Thu Jan 14, 2010 5:43 pm
Posts: 8
pb00067 wrote:
Which picture do you mean?


The one in the first post:

Image

(Hosted in another server)
Image
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CarlSagan
 Post subject: Re: How to create an identified 1xN relation ?
PostPosted: Sun Jan 24, 2010 10:23 am 
Newbie

Joined: Thu Jan 14, 2010 5:43 pm
Posts: 8
CarlSagan wrote:
pb00067 wrote:
Which picture do you mean?


The one in the first post:

Image

(Hosted in another server)
Image

No idea for this one?
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pb00067
 Post subject: Re: How to create an identified 1xN relation ?
PostPosted: Mon Jan 25, 2010 9:09 am 
Expert
Expert

Joined: Tue Jun 16, 2009 3:36 am
Posts: 990
I cannot see any attached image (tif, jpeg, gif or else)!
I checked my profile, but I think not id depends on my personal settings ...
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CarlSagan
 Post subject: Re: How to create an identified 1xN relation ?
PostPosted: Mon Jan 25, 2010 10:15 am 
Newbie

Joined: Thu Jan 14, 2010 5:43 pm
Posts: 8
pb00067 wrote:
I cannot see any attached image (tif, jpeg, gif or else)!
I checked my profile, but I think not id depends on my personal settings ...

Wow.

Try flickr then: http://www.flickr.com/photos/41696532@N06/4303156891/
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pb00067
 Post subject: Re: How to create an identified 1xN relation ?
PostPosted: Mon Jan 25, 2010 10:58 am 
Expert
Expert

Joined: Tue Jun 16, 2009 3:36 am
Posts: 990
Hm, apparently overlapping @Id + @javax.persistence.ManyToOne on the same property is not supported.

Code:
@Id
@javax.persistence.ManyToOne
protected Book bookId = null;


I get javax.persistence.PersistenceException: [PersistenceUnit: helloworld] Unable to build EntityManagerFactory
at org.hibernate.ejb.Ejb3Configuration.buildEntityManagerFactory(Ejb3Configuration.java:761)


Sorry, the solution with the IdClass does not work.

Anyway I personally prefer always the use of a surrogate generated key as primary key
and use NaturalId for any business keys (as bookid or edition) like I proposed.
Then i never face the problem you have.
And furthermore: if once I have to change the bookid value for a determinate book,
then I need not to update also other foreign keys.
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