java - A class that behaves like @Entity and @Embeddable

Question

I have a one way @OneToMany relationship between a Team and Player class. I would like to save a Team object among your Players. Player's identifier IS COMPOUND by Team foreign key and list index as follows. I have a mapping like this one because i need to save Team and your Players ate the same time.

@Entity
public class Team {

    @Id
    @GeneratedValue
    private Integer id;

    @CollectionOfElements
    @JoinTable(
        name="PLAYER",
        joinColumns=@JoinColumn(name="TEAM_ID"))
    @IndexColumn(name="PLAYER_INDEX")
    private List<Player> playerList = new ArrayList<Player>();

}

@Embeddable
public class Player {

   // Player's getter's and setter's

}

So if i use the following

Team team = new Team();

team.getPlayerList().add(new Player());
team.getPlayerList().add(new Player());

session.save(team); // It works!

It happens whether you use @CollectionsOfElements, Player class need a @Embeddable annotation, not a @Entity. JPA does not allows @Entity and @Embeddable at the same time. Player is also a @Entity - it has relationship with other entities.

Has someone an idea about i could save a Team and a Player (ONE WAY RELATIONSHIP) by using CascadeType.PERSIST with @Entity in the Player class instead of @Embeddable ?

Remember that COMPOUND primary key needs to be assigned before saving but Team's identifier and PlayerList index position could play the role of Player's compound primary key

regards,

Answer 1

The below solution shows a composite key for Player that consists of Team and the position in the list of players in that team. Saves cascade from team to players.

Team.java

import java.io.Serializable;
import java.util.ArrayList;
import java.util.List;

import javax.persistence.CascadeType;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.OneToMany;
import javax.persistence.Version;

import org.apache.commons.lang.builder.ToStringBuilder;
import org.apache.commons.lang.builder.ToStringStyle;
import org.hibernate.annotations.IndexColumn;

@Entity
public class Team implements Serializable {

    @Id @GeneratedValue private Long id;

    @Version private int version;

    @OneToMany(cascade=CascadeType.ALL, mappedBy="id.team")
    @IndexColumn(name="PLAYER_IDX")
    private List<Player> players = new ArrayList<Player>();

    private String name;

    protected Team() {}

    public Team(String name) {
        this.name = name;
    }

    public boolean addPlayer(Player player) {
        boolean result = players.add(player);
        if (result) {
            player.setPlayerId(new PlayerId(this, players.size() - 1));
        }
        return result;
    }

    public List<Player> getPlayers() {
        return players;
    }

    @Override
    public String toString() {
        return new ToStringBuilder(this, ToStringStyle.SHORT_PREFIX_STYLE).append("name", name).append("players", players).toString();
    }
}

Player.java

import java.io.Serializable;

import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.Version;

import org.apache.commons.lang.builder.ToStringBuilder;
import org.apache.commons.lang.builder.ToStringStyle;

@Entity
public class Player implements Serializable {

    @Id private PlayerId id;

    @Version private int version;

    void setPlayerId(PlayerId id) {
        this.id = id;
    }

    @Override
    public String toString() {
        return new ToStringBuilder(this, ToStringStyle.SHORT_PREFIX_STYLE).append("number", id.getNumber()).toString();
    }

}

PlayerId.java

import java.io.Serializable;

import javax.persistence.Column;
import javax.persistence.Embeddable;
import javax.persistence.ManyToOne;

import org.apache.commons.lang.builder.HashCodeBuilder;

@Embeddable
public class PlayerId implements Serializable {

    @ManyToOne
    private Team team;

    @Column(name="PLAYER_IDX", insertable=false, updatable=false)
    private int number;

    protected PlayerId() {}

    PlayerId(Team team, int number) {
        this.team = team;
        this.number = number;
    }

    public int getNumber() {
        return number;
    }

    @Override
    public boolean equals(Object obj) {
        if (obj == null) {
            return false;
        } else if (obj == this) {
            return true;
        } if (obj instanceof PlayerId) {
            PlayerId other = (PlayerId) obj;
            return other.team.equals(this.team) && other.number == this.number; 
        }
        return false;
    }

    @Override
    public int hashCode() {
        return new HashCodeBuilder().append(team).append(number).toHashCode();
    }

}

This test below:

public void testPersistTeamAndPlayers() throws Exception {
    Team team = new Team("My Team");
    team.addPlayer(new Player());
    team.addPlayer(new Player());

    AnnotationConfiguration configuration = new AnnotationConfiguration();
    configuration.addAnnotatedClass(Team.class);
    configuration.addAnnotatedClass(Player.class);
    configuration.configure();

    SessionFactory sessionFactory = configuration.buildSessionFactory();
    Session session;
    session = sessionFactory.openSession();
    Transaction transaction = session.beginTransaction();
    session.save(team);
    transaction.commit();
    session.close();

    session = sessionFactory.openSession();
    @SuppressWarnings("unchecked") List<Team> list = session.createCriteria(Team.class).list();
    assertEquals(1, list.size());

    Team persisted = list.get(0);
    System.out.println(persisted);

gives the following log output:

12:37:17,796 DEBUG [SchemaExport, SchemaExport.execute] 
    create table Player (
        PLAYER_IDX integer not null,
        version integer not null,
        team_id bigint,
        primary key (PLAYER_IDX, team_id)
    )
12:37:17,796 DEBUG [SchemaExport, SchemaExport.execute] 
    create table Team (
        id bigint generated by default as identity (start with 1),
        name varchar(255),
        version integer not null,
        primary key (id)
    )
12:37:17,796 DEBUG [SchemaExport, SchemaExport.execute] 
    alter table Player 
        add constraint FK8EA38701AA5DECBA 
        foreign key (team_id) 
        references Team
12:37:17,812 INFO  [SchemaExport, SchemaExport.importScript] Executing import script: /import.sql
12:37:17,812 INFO  [SchemaExport, SchemaExport.execute] schema export complete
12:37:17,859 DEBUG [SQL, SQLStatementLogger.logStatement] 
    insert 
    into
        Team
        (id, name, version) 
    values
        (null, ?, ?)
12:37:17,875 DEBUG [SQL, SQLStatementLogger.logStatement] 
    call identity()
12:37:17,875 DEBUG [SQL, SQLStatementLogger.logStatement] 
    select
        player_.PLAYER_IDX,
        player_.team_id,
        player_.version as version1_ 
    from
        Player player_ 
    where
        player_.PLAYER_IDX=? 
        and player_.team_id=?
12:37:17,890 DEBUG [SQL, SQLStatementLogger.logStatement] 
    select
        player_.PLAYER_IDX,
        player_.team_id,
        player_.version as version1_ 
    from
        Player player_ 
    where
        player_.PLAYER_IDX=? 
        and player_.team_id=?
12:37:17,890 DEBUG [SQL, SQLStatementLogger.logStatement] 
    insert 
    into
        Player
        (version, PLAYER_IDX, team_id) 
    values
        (?, ?, ?)
12:37:17,890 DEBUG [SQL, SQLStatementLogger.logStatement] 
    insert 
    into
        Player
        (version, PLAYER_IDX, team_id) 
    values
        (?, ?, ?)
12:37:17,906 DEBUG [SQL, SQLStatementLogger.logStatement] 
    select
        this_.id as id0_0_,
        this_.name as name0_0_,
        this_.version as version0_0_ 
    from
        Team this_
12:37:17,937 DEBUG [SQL, SQLStatementLogger.logStatement] 
    select
        players0_.team_id as team3_1_,
        players0_.PLAYER_IDX as PLAYER1_1_,
        players0_.PLAYER_IDX as PLAYER1_1_0_,
        players0_.team_id as team3_1_0_,
        players0_.version as version1_0_ 
    from
        Player players0_ 
    where
        players0_.team_id=?
Team[name=My Team,players=[Player[number=0], Player[number=1]]]

The last line shows the toString for Team and Player, which shows how the numbers are assigned (the index of the list). Other entities can refer the Player (by team_id and player_idx).