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@Entity
@Table(name="PLAYER")
@Inheritance(strategy=InheritanceType.SINGLE_TABLE)
@DiscriminatorColumn(
          name="TEAM", 
          discriminatorType=DiscriminatorType.STRING
          )
public abstract class Player{
    @Id
    @Column(name="ID")
    @GeneratedValue(generator = "seq_gen")
    @SequenceGenerator(name = "seq_gen", sequenceName = "CONSTANTS_SEQ")
    protected long id;
    @Column(name="NAME")
    protected String name;
    @Column(name="YEAR")
    protected int year; 
}

@Entity
@DiscriminatorValue(value = "SUNRISERS")
public class SunRisersPlayer extends Player{

}

@Entity
@DiscriminatorValue(value = "KNIGHT_RIDERS")
public class KnightRidersPlayer extends Player{

}

@Entity
@DiscriminatorValue(value = "DARE_DEVILS")
public class DareDevilsPlayer extends Player{

}

Here, I am trying to fetch all team players at once 

public interface PlayerDao extends CrudRepository<Player, Long>{

    List<Player> findAll();
}

Sample PLAYER Table Data is 

ID      name        year    team
1000    gilchrist   2015    SUNRISERS
1001    Yuvraj      2015    SUNRISERS
1002    Ghambir     2015    KNIGHT_RIDERS
1004    Pathan      2015    KNIGHT_RIDERS
1006    Umesh       2015    KNIGHT_RIDERS
1007    Zaheer      2015    DARE_DEVILS
1008    Venu        2015    DARE_DEVILS

Once I get the complete list, how to prepare a Map in Java 8 with the key as Team name and value as a list of players corresponding to that team?

pbk
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  • Just don't use inheritance. Use a single TeamPlayer entity (use the singular form, BTW, not the plural form), and add a field named team to this entity. – JB Nizet Jun 25 '17 at 16:19
  • Thanks, changed it to singular form, I was trying to use a single table inheritance example in this case. – pbk Jun 25 '17 at 19:53
  • Why use inheritance if the subclasses don't have any additional field, nor any different behavior? – JB Nizet Jun 25 '17 at 20:17
  • I was trying to use hibernate features. I thought this would fit in this place. So, In which scenarios we can use this inheritance mapping? – pbk Jun 25 '17 at 21:40
  • When inheritance makes sense, i.e. when you have two entities, with an is-a association, and the sub-entity does things differently from the base one and has additional persistent properties. – JB Nizet Jun 26 '17 at 06:00

1 Answers1

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I was able to use groupBy to get the complete list as shown below

Defined a transient variable in Player entity to get the team name

@Transient
public String getName(){
    DiscriminatorValue val = this.getClass().getAnnotation( DiscriminatorValue.class );
    return val == null ? null : StringUtils.remove(WordUtils.capitalizeFully(val.value(), '_'), "_");
}

By using team Name, I am grouping by as shown below to get the players for each team (Map<String, List<Player>>)

List<Player> players = playerDaoImpl.findAll();
Map<String, List<Player>> playersPerTeam= players.stream()
              .collect(Collectors.groupingBy(Player::getName));
pbk
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