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From plins...@gmail.com
Subject Re: Trouble understanding JOINs
Date Thu, 29 Nov 2007 10:36:33 GMT
Hi Jacek,

Based on that description, it sounds like a bug in OpenJPA's list
handling somewhere.

Do the SQL statements issued differ?

-Patrick

On 11/28/07, Jacek Laskowski <jacek@laskowski.net.pl> wrote:
> Hi,
>
> I've got two entities: Osoba (Whole) and Konto (Part) in OneToMany
> association. Each contains id and name attributes. I decided to test
> inner and left fetch joins.
>
> I created 2 Osoba's, but only one got 2 Konto's.
>
> When I run
>
> SELECT o FROM Osoba o
>
> it returns 2 entities which is fine. However, when I run
>
> SELECT o FROM Osoba o JOIN FETCH o.konta
>
> it returns 1 entity which is still fine but the number of Konta
> entities is...4 (!).
>
> When I changed the type of Osoba.konta (plural of konto in Polish)
> from List<Konto> to Set<Konto> the above query returned 2 which was
> what I had first expected.
>
> Could anyone explain it to me? I seem to be missing some SQL classes
> on how joins are supposed to work so any pointers to documentation
> would be fine too.
>
> Here the entities go (with Set<Konto>):
>
> package pl.jaceklaskowski.jpa;
>
> import java.io.Serializable;
> import java.util.HashSet;
> import java.util.Set;
> import javax.persistence.CascadeType;
> import javax.persistence.Entity;
> import javax.persistence.GeneratedValue;
> import javax.persistence.GenerationType;
> import javax.persistence.Id;
> import javax.persistence.NamedQueries;
> import javax.persistence.NamedQuery;
> import javax.persistence.OneToMany;
>
> @Entity
> @NamedQueries({
>     @NamedQuery(name = "Osoba.poImieniu", query = "SELECT o FROM Osoba
> o WHERE o.imie = :imie"),
>     @NamedQuery(name = "Osoba.wszystkieOsoby", query = "SELECT o FROM Osoba
> o"),
>     @NamedQuery(name = "Osoba.wszystkieOsoby.JOIN_FETCH", query =
> "SELECT o FROM Osoba o JOIN FETCH o.konta"),
>     @NamedQuery(name = "Osoba.wszystkieOsoby.LEFT_JOIN_FETCH", query =
> "SELECT o FROM Osoba o LEFT JOIN FETCH o.konta")
> })
> public class Osoba implements Serializable {
>
>     private static final long serialVersionUID = 1L;
>     private int id;
>     private String imie;
>     private Set<Konto> konta = new HashSet<Konto>();
>
>     protected Osoba() {
>     }
>
>     public Osoba(String imie) {
>         this.imie = imie;
>     }
>
>     @Id
>     @GeneratedValue(strategy = GenerationType.AUTO)
>     public int getId() {
>         return id;
>     }
>
>     public void setId(int id) {
>         this.id = id;
>     }
>
>     @OneToMany(cascade=CascadeType.PERSIST)
>     public Set<Konto> getKonta() {
>         return konta;
>     }
>
>     public void setKonta(Set<Konto> konta) {
>         this.konta = konta;
>     }
>
>     public void addKonto(Konto konto) {
>         getKonta().add(konto);
>     }
>
>     public String getImie() {
>         return imie;
>     }
>
>     public void setImie(String imie) {
>         this.imie = imie;
>     }
>
>     @Override
>     public String toString() {
>         return "Osoba[id=" + getId() + "]";
>     }
> }
>
> package pl.jaceklaskowski.jpa;
>
> import java.io.Serializable;
> import javax.persistence.Entity;
> import javax.persistence.GeneratedValue;
> import javax.persistence.GenerationType;
> import javax.persistence.Id;
>
> @Entity
> public class Konto implements Serializable {
>
>     private static final long serialVersionUID = 1L;
>     private int id;
>     private String numer;
>
>     protected Konto() {
>     }
>
>     public Konto(String numer) {
>         this.numer = numer;
>     }
>
>     @Id
>     @GeneratedValue(strategy = GenerationType.AUTO)
>     public int getId() {
>         return id;
>     }
>
>     public void setId(int id) {
>         this.id = id;
>     }
>
>     public String getNumer() {
>         return numer;
>     }
>
>     public void setNumer(String numer) {
>         this.numer = numer;
>     }
>
>     @Override
>     public String toString() {
>         return "Konto[id=" + getId() + "]";
>     }
> }
>
> Jacek
>
> --
> Jacek Laskowski
> http://www.JacekLaskowski.pl
>


-- 
Patrick Linskey
202 669 5907

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