使用 Eclipselink JPA 通过代码（不是 ID）链接两个对象

Question

我有两个 table：

area (
  id int PK autoincrement
  code varchar
)

products (
  id int PK autoincrement
  area_id int
)

对象定义如下：

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

这很好用，但我希望该区域是一个字符串，其中包含 table area 列 code[=25= 中使用的代码].

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

注释应该是什么才能使这项工作正常进行？

谢谢！

Answer 1

尝试使用 @SecondaryTable and @Column 注释的组合。像这样：

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

Answer 2

如果有同样问题的可怜人，我是这样做的：

使用变压器。所以字段区域是这样定义的：

@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;

那么这些类的工作方式如下：

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;
}

}

AreaFieldTransformer

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;
}

}

使用 Eclipselink JPA 通过代码（不是 ID）链接两个对象

Linking two object by code (not ID) using Eclipselink JPA

jpa

eclipselink