java Embeddable 类中的外键映射
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Foreign key mapping inside Embeddable class
提问by Ahamed
I am using eclipselinkfor JPA. I have an entity, which has a composite keyfabricated out of two fields. Following is my Embeddableprimary key class' fields(members).
我正在使用eclipselinkfor JPA。我有一个实体，它有一个由两个字段组成的复合键。以下是我的Embeddable主键类的字段（成员）。
@Embeddable
public class LeavePK {
@ManyToOne(optional = false)
@JoinColumn(name = "staffId", nullable = false)
private Staff staff;
@Temporal(TemporalType.TIMESTAMP)
private Calendar date;
//setters and getters
}
My entity is going to hold leave data related to a staff, so I am trying to combine staff object and leave date to produce composite key. Apart from my logic, it is not allowing me to have a foreign key mapping inside embeddable class. When I try to use JPA tools--> Generate Tables From Entity, it gives error as below, which explains, but I am not getting it.
我的实体将保存与员工相关的休假数据，因此我尝试将员工对象和休假日期结合起来以生成复合键。除了我的逻辑之外，它不允许我在可嵌入类中有外键映射。当我尝试使用JPA tools--> Generate Tables From Entity 时，它给出了如下错误，这解释了，但我没有得到它。
org.eclipse.persistence.exceptions.ValidationException
Exception Description: The mapping [staff] from the embedded ID class [class rs.stapp.entity.LeavePK] is an invalid mapping for this class. An embeddable class that is used with an embedded ID specification (attribute [leavePK] from the source [class rs.stapp.entity.Leave]) can only contain basic mappings. Either remove the non basic mapping or change the embedded ID specification on the source to be embedded.
Does it mean, I cannot have a key(from composite key) which is also a foreign key. Is there a alternative way to accomplish this ERM? Please help. Thanks
这是否意味着，我不能有一个也是外键的键（来自复合键）。有没有其他方法来完成这个 ERM？请帮忙。谢谢
回答by Kawu
Don't put relationships into ID classes, neither for @IdClassor @EmbeddedIdones. An @Embeddableclass may only include the annotations @Basic, @Column, @Temporal, @Enumerated, @Lob, or @Embedded. Everything else is provider-specific syntax (e.g. Hibernate allows this, but since you're using EclipseLink, which is the JPA RI, I doubt this is what you want).
不要将关系放入 ID 类中，无论是 for@IdClass还是@EmbeddedIdone。一@Embeddable类可能只包括注释@Basic，@Column，@Temporal，@Enumerated，@Lob，或@Embedded。其他一切都是提供者特定的语法（例如，Hibernate 允许这样做，但由于您使用的是 EclipseLink，即 JPA RI，我怀疑这是否是您想要的）。
Here's an example JPA PK/FK mapping:
这是一个 JPA PK/FK 映射示例：
@Entity
@Table(name = "Zips")
public class Zip implements Serializable
{
@EmbeddedId
private ZipId embeddedId;
@ManyToOne
@JoinColumn(name = "country_code", referencedColumnName = "iso_code")
private Country country = null;
...
}
@Embeddable
public class ZipId implements Serializable
{
@Column(name = "country_code")
private String countryCode;
@Column(name = "code")
private String code;
...
}
HTH
HTH
