java - JPA 集合在映射表中有不需要的唯一约束

Question

当我使用 hibernate.hbm2ddl.auto=create 自动生成我的数据库时，在映射表中创建了一个“不需要的”唯一约束。我正在运行 postgres 9.1，创建表语句变为:

CREATE TABLE schemaname.scanalerts
(
  scanid bigint NOT NULL,
  alerts_id bigint NOT NULL,
  CONSTRAINT fkd65bd7541b5b1a8e FOREIGN KEY (scanid)
      REFERENCES rfid.scan (id) MATCH SIMPLE
      ON UPDATE NO ACTION ON DELETE NO ACTION,
  CONSTRAINT fkd65bd754860b0886 FOREIGN KEY (alerts_id)
      REFERENCES rfid.alert (id) MATCH SIMPLE
      ON UPDATE NO ACTION ON DELETE NO ACTION,
  CONSTRAINT scanalerts_alerts_id_key UNIQUE (alerts_id ),
  CONSTRAINT scanalerts_scanid_alerts_id_key UNIQUE (scanid , alerts_id )
)

不需要的约束是 CONSTRAINT scanalerts_alerts_id_key UNIQUE (alerts_id )，基本上我只想要 scanid 和 alerts_id 的唯一约束。

我正在使用 JPA 注释来创建映射，这是我的代码:

@ElementCollection(targetClass = Alert.class, fetch = FetchType.EAGER)
@CollectionTable(name = "scanalerts", schema = RfidConstants.SCHEMA, 
    joinColumns = @JoinColumn(name = "scanid"), 
    uniqueConstraints = @UniqueConstraint(columnNames = { "scanid", "alerts_id" }))
private List<Alert> alerts;

有什么方法可以停止创建 alert_id 唯一约束吗？

谢谢

@JBNizet 这是警报映射注释:

@Entity
@Table(name = "alert", schema = "schemaname", 
    uniqueConstraints = @UniqueConstraint(columnNames = {"message", "alertPriority"}) )
public class Alert implements Serializable {

    @Id
    @Column(name="id")
    @SequenceGenerator(name = "alertSeq", sequenceName="ALERT_SEQ", allocationSize = 1)
    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "alertSeq")
    private Long id;

    @Column(name="versionnum")
    @Version
    private Long version;

    @Column(name = "message", nullable = false)
    private String message;

    @Column(name = "alertpriority", nullable = false)
    @Enumerated(EnumType.STRING)
    private AlertPriority alertPriority;

Answer 1

如 JavaDocs 中的示例所述, @ElementCollection用于映射基本类型或可嵌入对象的集合。 Alert是一个实体，因此 List<Alert>不是基本类型或可嵌入对象的集合。

因为由 scanid 组成的唯一约束和 alert_id是首选，我假设 Scan 之间的关系和 Alert确实具有多对多的性质。那 可以实现如下:

@ManyToMany
@JoinTable(name = "scanalerts",  schema = RfidConstants.SCHEMA,
  joinColumns = @JoinColumn(name = "scanid"),
  inverseJoinColumns = @JoinColumn(name = "alert_id")
)
private List<Alert> alerts;

表的主键包含两列，这就是使用 @UniqueConstraint 的原因不需要。