[JPA - Hibernate] OneToMany without join table

[Gregg Bolinger]

I have 2 Objects for this question.

Color.java
--id
--name
--description

--@OneToMany
private List<ProductAttributes> attributes;

ProductAttributes.java
--id
--Color color

JPA is generating the Color and ProductAttributes tables but also it is creating a Color_ProductAttributes table. This table doesn't really need to be there, I don't think. So questions:

1. How to set up the annotations so that this table is not created
2. Will it perform better with/without the join table?

[Gregg Bolinger]

Found my solution here.

Thanks.

[Rahul Juneja]

What if you want to make it as unidirectional without a join table.

Thanks,
Rahul

[Cameron Wallace McKenzie]

Indeed, this is actually the default behavior for one to many associations, although it seems a bit weird when a simple foreign key would do.

I've got a simple "Team has many Players" mapping on my website that uses a database like this:




Mapping Many to One and One to Many Associations without a join table

The code is pretty straight forward:

  import javax.persistence.*;
@Entity
public class Player { 
 private long id;
 private String nickName;
 private Team team;
 
 @ManyToOne
 @JoinColumn(name="team_id")      
 public Team getTeam() {return team;}
 public void setTeam(Team t) {this.team = t;}
 @Id
 @GeneratedValue
 public long getId() {return id;}
 public void setId(long id) {this.id = id;}
 public String getNickName() {return nickName;}
 public void setNickName(String n) {nickName = n;}
}
  

  import java.util.List; import javax.persistence.*;
@Entity
public class Team {
 private long id; 
 private String name;
 private List<Player> players; 
 
 @OneToMany(mappedBy="team",  
              targetEntity=Player.class, 
    fetch=FetchType.EAGER, cascade = CascadeType.ALL)
 public List<Player> getPlayers() {return players;}
 public void setPlayers(List<Player> p){players=p;}
 @Id
 @GeneratedValue
 public long getId() {return id;}
 public void setId(long id) {this.id = id;}
 public String getName() {return name;}
 public void setName(String name) {this.name = name;}
}
  

  public static void main(String args[]){
    HibernateUtil.recreateDatabase();
    Session session=HibernateUtil.beginTransaction();
 
    Team team = new Team();
    Player p1 = new Player();
    Player p2 = new Player();
 
    session.save(team);
    session.save(p1);
    session.save(p2);
 
    team.setName("Pickering Atoms");
    p1.setNickName("Lefty");
    p1.setTeam(team);
    p2.setNickName("Blinky");
    p2.setTeam(team);
    HibernateUtil.commitTransaction();
  }
   

Mapping Many to One and One to Many Associations without a join table

That Join Column annotation is really what does the trick.

-Cameron McKenzie

[Gregg Bolinger]

Cameron,

If you had read the thread you would know that I already stated that I found the solution and linked to the very same page you are linking to.