Java – establish a two to many relationship in JPA / hibernate

I have the following physical relationship issues The game must have two (only two) team objects "Team" can have many "games"

As far as I can see, this is a two - to - many relationship However, I don't know how to model in JPA For example, I want to do such a thing

@Entity
public class Team extends BaSEObject {
  private Long id;
  private Set<Game> games;

  @Id
  @GeneratedValue(strategy = GenerationType.AUTO) 
  public Long getId() {return id;}
  public void setId(Long id) {this.id = id;}

  @OneToMany(mappedBy = "game")
  public Set<Game> getGames() {return games;}
  public void setGames(Set<Game> games) {this.games = games;}
}

@Entity
public class Game extends BaSEObject {
  private Long id;
  private Team team1;
  private Team team2;

  @Id
  @GeneratedValue(strategy = GenerationType.AUTO) 
  public Long getId() {return id;}
  public void setId(Long id) {this.id = id;}

  @ HERE IS THE PROBLEM - WHAT ANNOTATION DO I USE?
  public Team getTeam1() {return team1;}
  public void setTeam1(Team team1) {this.team1 = team1;}

  @ HERE IS THE PROBLEM - WHAT ANNOTATION DO I USE?
  public Team getTeam2() {return team2;}
  public void setTeam2(Team team1) {this.team2 = team2;}
}

However, as you can see, I don't know how to join tables together in terms of annotations Has anyone ever done such a thing? Any ideas, help?

Thank you.

Solution

I want someone to come up with a great solution, but it's a tricky situation. I've never found a way to map well Your choices include:

>Change the way you build relationships For example, you can do this:

@Entity
public class GameMembership {
   Team team;
   Game game;
   int gamePosition; // If tracking Team 1 vs Team 2 matters to you
}

Then the game has a set < gamemembership >, that is, you model it as many to many The game can still have convenient methods to set team 1 and team 2 (business logic forces only two teams, but they have been completed), but they are mapped back to the collection used by hibernate Abandoning a relationship is two-way – choosing a direction (game → team seems most appropriate) only moves the relationship Find a game that the team participates in and then becomes an operation such as your Dao, rather than an operation that the team itself can access:

public class GameDAO {
    ....
    public Collection<Game> gamesForTeam(Team t) {
         ....
         Query q = session.createQuery("FROM Game WHERE team1 = :team OR team2 = :team");
         q.setParameter("team",t);
         return q.list();
    }
}

Or something like that... > continue along your route, but "cheat" at the end of the team The attributes of the game end should be mapped to the normal many to one relationship; Then use mappedby on the team side to represent the control relationship of the game

public class Team {
        ...
        @OneToMany(mappedBy="team1")
        private Set<Game> team1Games;
        @OneToMany(mappedBy="team2")
        private Set<Game> team2Games;

Then provide convenient properties for your API (team1games and team2games are for hibernate only):

@Transient
    public Set<Game> getGames() {
        Set<Game> allGames = new HashSet<Game>(team1Games);
        allGames.addAll(team2Games);
        // Or use google-collections Sets.union() for bonus points
        return allGames;
    }

So your class caller, it is transparent and has two attributes