使用Eclipselink JPA通过代码（非ID）链接两个对象

我有两张桌子：

area (
  id int PK autoincrement
  code varchar
)

products (
  id int PK autoincrement
  area_id int
)

对象的定义如下：

class Product {
    ...
    @JoinColumn(name = "area_id", referencedColumnName = "id")
    @ManyToOne
    @Expose
    private Area area;
    ...    
}

@Entity    
@SecondaryTable(name="area", pkJoinColumns=@PrimaryKeyJoinColumn(name="id", referencedColumnName="area_id"))
class Product {
    ...
    @Column(name="code", table = "area")
    private String code;
    ...
}

@Transformation(fetch = FetchType.EAGER, optional = false)
@ReadTransformer(transformerClass = AreaAttributeTransformer.class)
@WriteTransformers({
        @WriteTransformer(
                transformerClass = AreaFieldTransformer.class,
                column = @Column(name = "area_id", nullable = false))
})
@Expose
private String area;

这很好，但我希望该区域是一个字符串，包含表area列code中使用的代码

class Product {
    ...
    ???
    private String area;
    ...    
}

什么样的注释才能使这项工作有效

---

谢谢

尝试使用和注释的组合。大概是这样的：

class Product {
    ...
    @JoinColumn(name = "area_id", referencedColumnName = "id")
    @ManyToOne
    @Expose
    private Area area;
    ...    
}

@Entity    
@SecondaryTable(name="area", pkJoinColumns=@PrimaryKeyJoinColumn(name="id", referencedColumnName="area_id"))
class Product {
    ...
    @Column(name="code", table = "area")
    private String code;
    ...
}

@Transformation(fetch = FetchType.EAGER, optional = false)
@ReadTransformer(transformerClass = AreaAttributeTransformer.class)
@WriteTransformers({
        @WriteTransformer(
                transformerClass = AreaFieldTransformer.class,
                column = @Column(name = "area_id", nullable = false))
})
@Expose
private String area;

---

如果有一个可怜的灵魂也有同样的问题，我是这样做的：

使用变压器。因此，字段区域的定义如下：

class Product {
    ...
    @JoinColumn(name = "area_id", referencedColumnName = "id")
    @ManyToOne
    @Expose
    private Area area;
    ...    
}

@Entity    
@SecondaryTable(name="area", pkJoinColumns=@PrimaryKeyJoinColumn(name="id", referencedColumnName="area_id"))
class Product {
    ...
    @Column(name="code", table = "area")
    private String code;
    ...
}

@Transformation(fetch = FetchType.EAGER, optional = false)
@ReadTransformer(transformerClass = AreaAttributeTransformer.class)
@WriteTransformers({
        @WriteTransformer(
                transformerClass = AreaFieldTransformer.class,
                column = @Column(name = "area_id", nullable = false))
})
@Expose
private String area;

然后这些类别的工作原理如下：

class Product {
    ...
    @JoinColumn(name = "area_id", referencedColumnName = "id")
    @ManyToOne
    @Expose
    private Area area;
    ...    
}

@Entity    
@SecondaryTable(name="area", pkJoinColumns=@PrimaryKeyJoinColumn(name="id", referencedColumnName="area_id"))
class Product {
    ...
    @Column(name="code", table = "area")
    private String code;
    ...
}

@Transformation(fetch = FetchType.EAGER, optional = false)
@ReadTransformer(transformerClass = AreaAttributeTransformer.class)
@WriteTransformers({
        @WriteTransformer(
                transformerClass = AreaFieldTransformer.class,
                column = @Column(name = "area_id", nullable = false))
})
@Expose
private String area;

AreaAttributeTransformer

public class AreaAttributeTransformer implements AttributeTransformer {

private AbstractTransformationMapping mapping;

@Override
public void initialize(AbstractTransformationMapping abstractTransformationMapping) {
    this.mapping = abstractTransformationMapping;
}


@Override
public Object buildAttributeValue(Record record, Object o, Session session) {
    for (DatabaseField field : mapping.getFields()) {
        if (field.getName().contains("area_id")) {

            EntityManager em = MyEntityManagerFactory.getENTITY_MANAGER_FACTORY().createEntityManager();
            List results = em.createNamedQuery("Areas.findById")
                    .setParameter("id", record.get(field))
                    .getResultList();
            if (results.size() > 0)
                return ((Area) results.get(0)).getCode();
        }
    }
    return null;
}

public class AreaFieldTransformer implements  FieldTransformer {

private AbstractTransformationMapping mapping;

@Override
public void initialize(AbstractTransformationMapping abstractTransformationMapping) {
    this.mapping = abstractTransformationMapping;
}

@Override
public Object buildFieldValue(Object o, String s, Session session) {
    if (o instanceof RouSub) {
        EntityManager em = MyEntityManagerFactory.getENTITY_MANAGER_FACTORY().createEntityManager();
        List results = em.createNamedQuery("Area.findByCode")
                .setParameter("area", ((Area) o).getCode())
                .getResultList();
        if (results.size() > 0)
            return ((Area)results.get(0)).getId();
    }
    return null;
}

}

AreaFieldTransformer

public class AreaAttributeTransformer implements AttributeTransformer {

private AbstractTransformationMapping mapping;

@Override
public void initialize(AbstractTransformationMapping abstractTransformationMapping) {
    this.mapping = abstractTransformationMapping;
}


@Override
public Object buildAttributeValue(Record record, Object o, Session session) {
    for (DatabaseField field : mapping.getFields()) {
        if (field.getName().contains("area_id")) {

            EntityManager em = MyEntityManagerFactory.getENTITY_MANAGER_FACTORY().createEntityManager();
            List results = em.createNamedQuery("Areas.findById")
                    .setParameter("id", record.get(field))
                    .getResultList();
            if (results.size() > 0)
                return ((Area) results.get(0)).getCode();
        }
    }
    return null;
}

public class AreaFieldTransformer implements  FieldTransformer {

private AbstractTransformationMapping mapping;

@Override
public void initialize(AbstractTransformationMapping abstractTransformationMapping) {
    this.mapping = abstractTransformationMapping;
}

@Override
public Object buildFieldValue(Object o, String s, Session session) {
    if (o instanceof RouSub) {
        EntityManager em = MyEntityManagerFactory.getENTITY_MANAGER_FACTORY().createEntityManager();
        List results = em.createNamedQuery("Area.findByCode")
                .setParameter("area", ((Area) o).getCode())
                .getResultList();
        if (results.size() > 0)
            return ((Area)results.get(0)).getId();
    }
    return null;
}

---

}

为什么不保留映射并在需要代码时使用area.code呢？我正在实现json rest API，我想让它尽可能简单。我希望用户只发送代码，而不需要知道area.id是什么。不要将实体类和webservices类混合在一起，这样您就不会有这样的问题。您的EJB类应该只对数据库建模，您需要为Web服务创建另一组类，并在它们之间映射数据！谢谢你的回复。这对于GET方法很有效，但是PUT呢？异常说明：缺少字段[area.id]的映射。Descriptor:RelationalDescriptor（xxx.Product-->[DatabaseTable（products），DatabaseTable（area）]@MarianoL您是否尝试使用已存在或不存在的区号保存新产品？另外，请看一下这个问题