从本机查询和转换中检索数据 [英] Retrieving data from native query and conversion
问题描述
我有以下查询
@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());
}
据我所知,
哪个返回String的列表?由于错误,我得到
which as far as I am aware it return list of String? due to the error I am getting
由以下原因引起:java.lang.ClassCastException:java.lang.String无法强制转换为entity.Player 在utils.SessionFacade.copyPlayersToDetails(SessionFacade.java:105)
Caused by: java.lang.ClassCastException: java.lang.String cannot be cast to entities.Player at utils.SessionFacade.copyPlayersToDetails(SessionFacade.java:105)
抛出错误的类可以很好地用于查询,该查询返回播放器字符串,例如从播放器返回*
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;
}
我该如何转换此方法,或者(如果可能)如何将存储在此String列表中的那些值保存到JSF页面中,以便检索查询结果?
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?
推荐答案
您的copyPlayersToDetails()
方法需要一个Player
实体列表,而不是一个String
列表.这就是为什么在这里获得ClassCastException
的原因:
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();
因为i.next()
返回String
.您的Java编译器没有抱怨的原因是因为 Query.getResultList()
(不幸的是)返回原始类型列表.
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.
您应将本机查询更改为此:
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());
}
进一步的批评
- 您应该(可能)使用绑定变量
- 您不需要加入
Game
表 - You should (probably) use a bind variable
- You don't need to join the
Game
table
Further criticism
改为写这个:
@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());
}
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