我想知道如何使用 EclipseLink 在 JPA 2中实现临时表。我所说的时间是指定义有效期的表格。
我面临的一个问题是引用表不能再对被引用表（临时表）有外键约束，因为被引用表的性质现在它们的主键包括有效期。
- 我将如何映射我的实体的关系？
- 这是否意味着我的实体不再与那些有效时间实体有关系？
- 现在初始化这些关系的责任是否应该由我在某种服务或专门的 DAO 中手动完成？
我发现的唯一东西是一个名为DAO Fusion的框架来处理这个问题。
- 有没有其他方法可以解决这个问题？
- 您能否提供有关此主题的示例或资源（带有时态数据库的 JPA）？
这是一个数据模型及其类的虚构示例。它从一个不需要处理时间方面的简单模型开始：
第一种情况：非时间模型
数据模型：
团队：
@Entity
public class Team implements Serializable {
private Long id;
private String name;
private Integer wins = 0;
private Integer losses = 0;
private Integer draws = 0;
private List<Player> players = new ArrayList<Player>();
public Team() {
}
public Team(String name) {
this.name = name;
}
@Id
@GeneratedValue(strategy=GenerationType.SEQUENCE, generator="SEQTEAMID")
@SequenceGenerator(name="SEQTEAMID", sequenceName="SEQTEAMID", allocationSize=1)
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
@Column(unique=true, nullable=false)
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Integer getWins() {
return wins;
}
public void setWins(Integer wins) {
this.wins = wins;
}
public Integer getLosses() {
return losses;
}
public void setLosses(Integer losses) {
this.losses = losses;
}
public Integer getDraws() {
return draws;
}
public void setDraws(Integer draws) {
this.draws = draws;
}
@OneToMany(mappedBy="team", cascade=CascadeType.ALL)
public List<Player> getPlayers() {
return players;
}
public void setPlayers(List<Player> players) {
this.players = players;
}
@Override
public int hashCode() {
final int prime = 31;
int result = 1;
result = prime * result + ((name == null) ? 0 : name.hashCode());
return result;
}
@Override
public boolean equals(Object obj) {
if (this == obj)
return true;
if (obj == null)
return false;
if (getClass() != obj.getClass())
return false;
Team other = (Team) obj;
if (name == null) {
if (other.name != null)
return false;
} else if (!name.equals(other.name))
return false;
return true;
}
}
播放器：
@Entity
@Table(uniqueConstraints={@UniqueConstraint(columnNames={"team_id","number"})})
public class Player implements Serializable {
private Long id;
private Team team;
private Integer number;
private String name;
public Player() {
}
public Player(Team team, Integer number) {
this.team = team;
this.number = number;
}
@Id
@GeneratedValue(strategy=GenerationType.SEQUENCE, generator="SEQPLAYERID")
@SequenceGenerator(name="SEQPLAYERID", sequenceName="SEQPLAYERID", allocationSize=1)
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
@ManyToOne
@JoinColumn(nullable=false)
public Team getTeam() {
return team;
}
public void setTeam(Team team) {
this.team = team;
}
@Column(nullable=false)
public Integer getNumber() {
return number;
}
public void setNumber(Integer number) {
this.number = number;
}
@Column(unique=true, nullable=false)
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
@Override
public int hashCode() {
final int prime = 31;
int result = 1;
result = prime * result + ((number == null) ? 0 : number.hashCode());
result = prime * result + ((team == null) ? 0 : team.hashCode());
return result;
}
@Override
public boolean equals(Object obj) {
if (this == obj)
return true;
if (obj == null)
return false;
if (getClass() != obj.getClass())
return false;
Player other = (Player) obj;
if (number == null) {
if (other.number != null)
return false;
} else if (!number.equals(other.number))
return false;
if (team == null) {
if (other.team != null)
return false;
} else if (!team.equals(other.team))
return false;
return true;
}
}
测试类：
@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration({"/META-INF/application-context-root.xml"})
@Transactional
public class TestingDao {
@PersistenceContext
private EntityManager entityManager;
private Team team;
@Before
public void setUp() {
team = new Team();
team.setName("The Goods");
team.setLosses(0);
team.setWins(0);
team.setDraws(0);
Player player = new Player();
player.setTeam(team);
player.setNumber(1);
player.setName("Alfredo");
team.getPlayers().add(player);
player = new Player();
player.setTeam(team);
player.setNumber(2);
player.setName("Jorge");
team.getPlayers().add(player);
entityManager.persist(team);
entityManager.flush();
}
@Test
public void testPersistence() {
String strQuery = "select t from Team t where t.name = :name";
TypedQuery<Team> query = entityManager.createQuery(strQuery, Team.class);
query.setParameter("name", team.getName());
Team persistedTeam = query.getSingleResult();
assertEquals(2, persistedTeam.getPlayers().size());
//Change the player number
Player p = null;
for (Player player : persistedTeam.getPlayers()) {
if (player.getName().equals("Alfredo")) {
p = player;
break;
}
}
p.setNumber(10);
}
}
现在您被要求保留团队和玩家在某个时间点的历史记录，因此您需要为每个要跟踪的表添加一个时间段。所以让我们添加这些时间列。我们将从Player.
第二个场景：时间模型
数据模型：
如您所见，我们必须删除主键并定义另一个包含日期（句点）的主键。我们还必须删除唯一约束，因为现在它们可以在表中重复。现在该表可以包含当前条目以及历史记录。
如果我们还必须使 Team temporal 变得非常难看，在这种情况下，我们需要删除Playertable 必须的外键约束Team。问题是您将如何在 Java 和 JPA 中对其进行建模。
请注意，ID 是代理键。但是现在代理键必须包含日期，因为如果不包含日期，则不允许存储同一实体的多个“版本”（在时间轴期间）。