如何使用 JPA 实现时态表？
2022-09-01 16:13:33
我想知道如何使用 EclipseLink 在 JPA 2 中实现临时表。通过时间，我的意思是定义有效期的表。
我面临的一个问题是，由于引用表的性质，引用表不能再对引用的表（临时表）具有外键约束，这些表现在的主键包括有效期。
- 如何映射实体的关系？
- 这是否意味着我的实体不能再与这些有效时间实体建立关系？
- 初始化这些关系的责任现在应该由我在某种服务或专门的DAO中手动完成吗？
我唯一找到的是一个名为DAO Fusion的框架，它处理这个问题。
- 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（具有临时数据库的 JPA）？
下面是数据模型及其类的虚构示例。它从一个简单的模型开始，不必处理时间方面：
第一种方案：非时态模型
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;
}
}
球员：
@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，系统会要求您保留团队和玩家在特定时间点的历史记录，因此您需要做的是为要跟踪的每个表添加一个时间段。因此，让我们添加这些时态列。我们将从 开始。Player
第二种方案：时态模型
数据模型：
如您所见，我们不得不删除主键并定义另一个包含日期（周期）的主键。此外，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和历史记录。
如果还必须使 Team 成为临时的，那么事情就会变得非常丑陋，在这种情况下，我们需要删除该表必须的外键约束。问题是你如何在Java和JPA中建模。PlayerTeam
请注意，ID 是代理项密钥。但是现在代理键必须包含日期，因为如果它们不包含日期，则不允许存储同一实体的多个“版本”（在时间轴期间）。
