问题
I have following query
@Override
public List<PlayerDetails> testPlayerQuerry() {
return copyPlayersToDetails(em.createNativeQuery("select player_name from player p\n"
+ "join Player_Game pg on p.player_id = pg.fk_player_id\n"
+ "join Game g on pg.fk_game_id = g.game_id\n"
+ "where g.game_id = 2").getResultList());
}
which as far as I am aware it return list of String? due to the error I am getting
Caused by: java.lang.ClassCastException: java.lang.String cannot be cast to entities.Player at utils.SessionFacade.copyPlayersToDetails(SessionFacade.java:105)
the class which throws the error it is working fine with queries which returns player String for example return * from players
private List<PlayerDetails> copyPlayersToDetails(List< Player> players) {
List<PlayerDetails> list = new ArrayList<PlayerDetails>();
Iterator i = players.iterator();
while (i.hasNext()) {
Player player = (Player) i.next();
PlayerDetails details = new PlayerDetails(player.getPlayerId(),
player.getPlayerName(), player.getPlayerRating());
list.add(details);
}
return list;
}
How I have to convert this method or how (if possible) I can get those values stored in this String list in to JSF page so I can retrieve the query results?
回答1:
Your copyPlayersToDetails()
method expects a list of Player
entities, not a list of String
. This is why you get a ClassCastException
here:
Player player = (Player) i.next();
Because i.next()
returns a String
. The reason why your Java compiler didn't complain is because Query.getResultList() (unfortunately) returns a raw type list.
You should change your native query to this:
@Override
public List<PlayerDetails> testPlayerQuerry() {
return copyPlayersToDetails(em.createNativeQuery("select p.* from player p\n"
+ "join Player_Game pg on p.player_id = pg.fk_player_id\n"
+ "join Game g on pg.fk_game_id = g.game_id\n"
+ "where g.game_id = 2", Player.class).getResultList());
}
Further criticism
- You should (probably) use a bind variable
- You don't need to join the
Game
table
Write this instead:
@Override
public List<PlayerDetails> testPlayerQuerry() {
return copyPlayersToDetails(em.createNativeQuery("select p.* from player p\n"
+ "join Player_Game pg on p.player_id = pg.fk_player_id\n"
+ "where pg.fk_game_id = :1", Player.class).setParameter(1, 2).getResultList());
}
来源:https://stackoverflow.com/questions/34666244/retrieving-data-from-native-query-and-conversion