The Many-To-Many Relationship in roster

The many-to-many relationship between Player and Team is specified by using the @ManyToMany annotation. In Team.java, the @ManyToMany annotation decorates the getPlayers method:

@ManyToMany
@JoinTable(
    name="EJB_ROSTER_TEAM_PLAYER",
    joinColumns=
        @JoinColumn(name="TEAM_ID", referencedColumnName="ID"),
    inverseJoinColumns=
        @JoinColumn(name="PLAYER_ID", referencedColumnName="ID")
)
public Collection<Player> getPlayers() {
    return players;
}

The @JoinTable annotation is used to specify a database table that will associate player IDs with team IDs. The entity that specifies the @JoinTable is the owner of the relationship, so the Team entity is the owner of the relationship with the Player entity. Because roster uses automatic table creation at deployment time, the container will create a join table named EJB_ROSTER_TEAM_PLAYER.

Player is the inverse, or nonowning, side of the relationship with Team. As one-to-one and many-to-one relationships, the nonowning side is marked by the mappedBy element in the relationship annotation. Because the relationship between Player and Team is bidirectional, the choice of which entity is the owner of the relationship is arbitrary.

In Player.java, the @ManyToMany annotation decorates the getTeams method:

@ManyToMany(mappedBy="players")
public Collection<Team> getTeams() {
    return teams;
}