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ManyToMany : how to save / find ?
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CrYoSoRe  
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 More options Apr 16 2010, 6:23 am
From: CrYoSoRe <pellet.aurel...@gmail.com>
Date: Fri, 16 Apr 2010 03:23:03 -0700 (PDT)
Local: Fri, Apr 16 2010 6:23 am
Subject: [play-framework] ManyToMany : how to save / find ?
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Hy.

I'm a newbie with JPA and i dont understand how can i use the
ManyToMany relation with Play  ?

Just see my code (in french i'm sorry):

/-------------------------------------------------------------------------- ---------/
package models;

import java.util.*;
import javax.persistence.*;

import play.db.jpa.*;

import models.FormatSiteWeb;
import models.MotCleSiteWeb;
import models.ThemeSiteWeb;

@Entity
/**
* Classe SiteWeb
* Classe utilisée pour stocker les différents site web references.
* @author a.pellet <pellet.aurel...@gmail.com>
* @see models.FormatSiteWeb;
* @since 2010/04/16
*/
public class SiteWeb extends Model {

        //
--------------------------------------------------------------------
        // Dependances avec les autres classes
        //
--------------------------------------------------------------------
        @ManyToOne
        public FormatSiteWeb formatDuSiteWeb;

        @ManyToMany
        public List<MotCleSiteWeb> listeDeMotsClesCorrespondantsAuSiteWeb;

        @ManyToOne
        public ThemeSiteWeb themeDuSiteWeb;

        //
--------------------------------------------------------------------
        // Proprietes de la classe.
        //
--------------------------------------------------------------------
                   public String nom;
        public String slogan;
        public String url;
        @Lob
        public String description;

        /**
        * Constructeur surcharge pour l'initialisation d'un site web.
        * @param String format
        * @param String nom
        * @param String slogan
        * @param String url
        * @param String description
        */
    public SiteWeb(FormatSiteWeb formatDuSiteWeb, ThemeSiteWeb
themeDuSiteWeb, String nom, String slogan, String url, String
description) {
                //
--------------------------------------------------------------------
                // Dependances avec les autres classes
                //
--------------------------------------------------------------------
                                      this.formatDuSiteWeb =
formatDuSiteWeb;
                this.listeDeMotsClesCorrespondantsAuSiteWeb = new
ArrayList<MotCleSiteWeb>();
                this.themeDuSiteWeb = themeDuSiteWeb;

                //
--------------------------------------------------------------------
                // Proprietes de la classe.
                //
--------------------------------------------------------------------
                this.nom = nom;
                this.slogan = slogan;
                this.url = url;
                this.description = description;
                this.nombreDePoint = nombreDePoint;

                   }

}

//------------------------------------------------------------------------- ----------------

package models;

import java.util.*;
import javax.persistence.*;

import play.db.jpa.*;

import models.SiteWeb;

@Entity
/**
* Classe MotsClesSiteWeb
* Classe utilisée pour stocker les différents mots clés des site web.
* @author a.pellet <pellet.aurel...@gmail.com>
* @see models.SiteWeb;
* @since 2010/04/15
*/
public class MotCleSiteWeb extends Model {

        //
--------------------------------------------------------------------
        // Dependances avec les autres classes
        //
--------------------------------------------------------------------
        @ManyToMany
        public List<SiteWeb> listeDeSiteWebCorrespondantsAuMotCle;

        //
--------------------------------------------------------------------
        // Proprietes de la classe.
        //
--------------------------------------------------------------------
                  public String nomDuMotCle;

        /**
        * Constructeur surcharge pour l'initialisation d'un mot cle.
        * @param String nom
        */
                   public MotCleSiteWeb(String nomDuMotCle) {
                //
--------------------------------------------------------------------
                // Dependances avec les autres classes
                //
--------------------------------------------------------------------
                this.listeDeSiteWebCorrespondantsAuMotCle = new
ArrayList<SiteWeb>();

                //
--------------------------------------------------------------------
                // Proprietes de la classe.
                //
--------------------------------------------------------------------
                                     this.nomDuMotCle = nomDuMotCle;
                   }

}

//------------------------------------------------------------------------- ---------------------

I have no probleme to save / find with ManyToOne or OneToMany but i
dont know how can i save / find on ManyToMany relation.

Someone have an exemple ?

Thanks.

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Guillaume Bort  
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 More options Apr 16 2010, 2:27 pm
From: Guillaume Bort <guillaume.b...@gmail.com>
Date: Fri, 16 Apr 2010 20:27:23 +0200
Local: Fri, Apr 16 2010 2:27 pm
Subject: Re: [play-framework] ManyToMany : how to save / find ?
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What is the problem exactly? Can you be more precise?

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Dam74  
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 More options Apr 17 2010, 5:07 am
From: Dam74 <damienhur...@hotmail.com>
Date: Sat, 17 Apr 2010 02:07:28 -0700 (PDT)
Local: Sat, Apr 17 2010 5:07 am
Subject: [play-framework] Re: ManyToMany : how to save / find ?
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When you map a same "ManyToMany relationShip" in both directions, you
need to tell which of these two directions is (kind of) the "master".
So : one of your @ManyToMany annotations must have the info :
"mappedBy" :

For example : if you have two entities : "Event" and "User", and a
User can "follow" several "Events",
and an Event can be followed by several Users ("ManyToMany
relationShip").

You would have :

in the entity User :
@ManyToMany(cascade=CascadeType.ALL)
    public Set<Event> followedEvents = new HashSet<Event>();

in the entity Event :
@ManyToMany(mappedBy="followedEvents")
    public Set<User> followsByUsers = new HashSet<User>();

A+ !

                       Dam74

On Apr 16, 12:23 pm, CrYoSoRe <pellet.aurel...@gmail.com> wrote:

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CrYoSoRe  
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 More options Apr 21 2010, 5:46 am
From: CrYoSoRe <pellet.aurel...@gmail.com>
Date: Wed, 21 Apr 2010 02:46:08 -0700 (PDT)
Local: Wed, Apr 21 2010 5:46 am
Subject: [play-framework] Re: ManyToMany : how to save / find ?
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@Dam74

Thanks for your help !

@Guillaume Bort

I just have some difficulty to understand the ManyToMany relation :)
(And it's not easy to explain a problem when you dont understand the
subject)

Maybe because in a OneToMany or ManyToOne there is an explicit
"master" - "slave" dependency ?

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