java - 对于没有 PK 的表，使用 JPA 组合键

Question

我需要一个包含客户端 ID、该 ID 的客户端(客户端)和客户端名称的客户端列表。问题是该表来自没有 PK 的 dblink

@Entity

@Table(name = "mytable", schema = "myschema")

public class Client {

    @Column(name = "clientid")
    @Id
    private Integer clientid;

    @Column(name = "client")
    private Integer client;

    @Column(name = "name")
    private String name;
}

使用这段代码，我会一遍又一遍地重复名字，直到列表末尾，因为没有 PK，如果没有 PK，我无法启动应用程序。当我将 client 列设置为 PK 时，会发生类似的情况(我正确获取所有名称，但 clientid 字段显示错误的值。是否有解决方法？

示例数据:

数据错误(将clientid设置为@Id时):

[
  {
    "clientid": 99,
    "client": 81,
    "name": "Organization 1"
  },
  {
    "clientid": 99,
    "client": 81,
    "name": "Organization 1"
  },
  {
    "clientid": 99,
    "client": 81,
    "name": "Organization 1"
  }
]

数据错误(将客户端设置为@Id时):

[
  {
    "clientid": 99,
    "client": 81,
    "name": "Organization 1"
  },
  {
    "clientid": 3,
    "client": 99,
    "name": "Organization 2"
  },
  {
    "clientid": 3,
    "client": 127,
    "name": "Organization 3"
  }
]

我应该得到什么:(clientid 在所有情况下都是正确的)

[
  {
    "clientid": 99,
    "client": 81,
    "name": "Organization 1"
  },
  {
    "clientid": 3,
    "client": 99,
    "name": "Organization 2"
  },
  {
    "clientid": 1,
    "client": 127,
    "name": "Organization 3"
  }
]

Answer 1

您应该创建一个复合键来正确处理您的数据。首先，创建另一个代表 key 的类:

public class ClientPK implements Serializable{

    private static final long serialVersionUID = 1L;

    private Integer clientid;

    private Integer client;

    /*Constructor, getters and setters here*/
}

然后更新类Client，如下所示:

@Entity
@Table(name = "mytable", schema = "myschema")
@IdClass(ClientPK.class)
public class Client {

    @Column(name = "clientid")
    @Id
    private Integer clientid;

    @Column(name = "client")
    private Integer client;

    @Column(name = "name")
    private String name;
}

最好在ClientPK类中实现hashCode和equals方法。