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Hibernate/JPA中如何合并实体集合？

正确合并集合并不是一件容易的事！推荐Vlad的例子文章的Spring Boot示例，只有手工进行集合合并。

关键点：

删除传入集合中不再存在的现有数据库行。
更新现有的可以在传入集合中找到的数据库行。
添加在传入集合中找到的行，这些行在当前数据库快照中是找不到的。

假设tournament和tennis_player两个表中有数据：

INSERT INTO tournament (id, name) VALUES (1, 'Roland Garros');
INSERT INTO tournament (id, name) VALUES (2, 'US Open');
INSERT INTO tennis_player (id, name, tournament_id) VALUES (1, 'Rafael Nadal', 1);
INSERT INTO tennis_player (id, name, tournament_id) VALUES (2, 'Roger Federer', 1);
INSERT INTO tennis_player (id, name, tournament_id) VALUES (3, 'David Ferer', 2);
INSERT INTO tennis_player (id, name, tournament_id) VALUES (4, 'Andy Murray', 2);
INSERT INTO tennis_player (id, name, tournament_id) VALUES (5, 'Del Potro', 2);
INSERT INTO tennis_player (id, name, tournament_id) VALUES (6, 'Novak D', 2);
INSERT INTO tennis_player (id, name, tournament_id) VALUES (7, 'John Isner', 2);

Tournament实体：和TennisPlayer 是双向一对多关系

@Entity
<b>public</b> <b>class</b> Tournament implements Serializable {

    <b>private</b> <b>static</b> <b>final</b> <b>long</b> serialVersionUID = 1L;

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    <b>private</b> Long id;

    <b>private</b> String name;

    @OneToMany(cascade = CascadeType.ALL, 
            mappedBy = <font>"tournament"</font><font>, orphanRemoval = <b>true</b>)
    <b>private</b> List<TennisPlayer> tennisPlayers = <b>new</b> ArrayList<>();
</font>

TennisPlayer 实体：

@Entity
<b>public</b> <b>class</b> TennisPlayer implements Serializable {

    <b>private</b> <b>static</b> <b>final</b> <b>long</b> serialVersionUID = 1L;

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    <b>private</b> Long id;

    <b>private</b> String name;

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = <font>"tournament_id"</font><font>)
    <b>private</b> Tournament tournament;
</font>

仓储：

@Repository
@Transactional(readOnly = <b>true</b>)
<b>public</b> <b>interface</b> TournamentRepository <b>extends</b> JpaRepository<Tournament, Long> { 
    
    @Query(value=<font>"SELECT t FROM Tournament t JOIN FETCH t.tennisPlayers WHERE t.name = ?1"</font><font>)
    Tournament tournamentAndPlayers(String name);
}

@Repository
@Transactional(readOnly = <b>true</b>)
<b>public</b> <b>interface</b> TennisPlayerRepository <b>extends</b> JpaRepository<TennisPlayer, Long> {

    @Query(value = </font><font>"SELECT p FROM TennisPlayer p JOIN p.tournament t WHERE t.name = ?1"</font><font>)
    List<TennisPlayer> playersOfTournament(String name);
}
</font>

在服务中进行两个实体集合的合并：

@Service
<b>public</b> <b>class</b> TennisService {

    <b>private</b> <b>final</b> TournamentRepository tournamentRepository;
    <b>private</b> <b>final</b> TennisPlayerRepository tennisPlayerRepository;

    <b>public</b> TennisService(TournamentRepository tournamentRepository,
            TennisPlayerRepository tennisPlayerRepository) {

        <b>this</b>.tournamentRepository = tournamentRepository;
        <b>this</b>.tennisPlayerRepository = tennisPlayerRepository;
    }

    <b>public</b> List<TennisPlayer> fetchPlayersOfTournament(String name) {

        <b>return</b> tennisPlayerRepository.playersOfTournament(name);
    }

    @Transactional
    <b>public</b> <b>void</b> updatePlayersOfTorunament(String name, List<TennisPlayer> players) {

        Tournament tournament = tournamentRepository.tournamentAndPlayers(name);
        System.out.println(<font>"-------------------------------------------------"</font><font>);

        </font><font><i>// Remove the existing database rows that are no </i></font><font>
        </font><font><i>// longer found in the incoming collection (players)</i></font><font>
        </font><font><i>//删除传入集合中不再存在的现有数据库行</i></font><font>
        tournament.getTennisPlayers().removeIf((t) -> !players.contains(t));

        </font><font><i>// Update the existing database rows which can be found </i></font><font>
        </font><font><i>// in the incoming collection (players)</i></font><font>
        </font><font><i>//更新现有的可以在传入集合中找到的数据库行</i></font><font>
</font>

        List<TennisPlayer> newPlayers = players.stream()
                .filter((t) -> !tournament.getTennisPlayers().contains(t))
                .collect(Collectors.toList());

        players.stream()
                .filter((t) -> !newPlayers.contains(t))                
                .forEach((t) -> {
                    t.setTournament(tournament);
                    TennisPlayer mergedPlayer = tennisPlayerRepository.save(t);
                    tournament.getTennisPlayers().set(
                            tournament.getTennisPlayers().indexOf(mergedPlayer),
                            mergedPlayer);
                });

        <font><i>// Add the rows found in the incoming collection, </i></font><font>
        </font><font><i>// which cannot be found in the current database snapshot</i></font><font>
        newPlayers.forEach((t) -> tournament.addTennisPlayer(t));
    }

}
</font>

手工合并集合的调用：

 System.out.println(<font>"------------------- Players from US Open --------------------"</font><font>);
            List<TennisPlayer> players = tennisService.fetchPlayersOfTournament(</font><font>"US Open"</font><font>);            
            
            players.forEach((t) -> System.out.println(</font><font>"Us Open: "</font><font> + t.getName() + </font><font>" | id:("</font><font> + t.getId() + </font><font>")"</font><font>));
            
            System.out.println(</font><font>"---------- Players from US Open Updated Detached ------------"</font><font>);
            
            </font><font><i>// ,update first player name</i></font><font>
            players.get(0).setName(</font><font>"Fernando Verdasco"</font><font>);
            
            </font><font><i>// remove second player</i></font><font>
            players.remove(1);
                        
            </font><font><i>// add a new player</i></font><font>
            TennisPlayer player = <b>new</b> TennisPlayer();
            player.setName(</font><font>"Alexander Zverev"</font><font>);
            players.add(player);
            
            players.forEach((t) -> System.out.println(</font><font>"Us Open: "</font><font> + t.getName() + </font><font>" | id:("</font><font> + t.getId() + </font><font>")"</font><font>));
            
            System.out.println(</font><font>"----------------- Players from US Open Merged ----------------"</font><font>);
            tennisService.updatePlayersOfTorunament(</font><font>"Us Open"</font><font>, players);
            
            players.forEach((t) -> System.out.println(</font><font>"Us Open: "</font><font> + t.getName() + </font><font>" | id:("</font><font> + t.getId() + </font><font>")"</font><font>));
</font>

源代码可以在这里找到。

原文 https://www.jdon.com/51798

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