Polymorphic CriteriaQuery没有反比关系 [英] Polymorphic CriteriaQuery without inverse relationship

问题描述

我有以下EJB结构。不要怀疑 Animal 和 Inventory ，这些类只是为了以简化的方式演示结构（更新：我修改了类名以构建一个更好理解的例子。 IdTag 的另一个实现可能是 BarcodeId ）。请注意， IdTag 与 Animal 或库存，让我们假设 RfidTag.code 是唯一的。我阅读使用条件查询检索多态Hibernate对象和 Hibernate多态查询但这些讨论似乎没有回答我的问题。

I have the following EJB structure. Don't wonder about Animal and Inventory, these classes are only here to demonstrate the structure in a simplified way (Update: I have revised the class names to construct a better understandable example. Another implementation of IdTag might be a BarcodeId). Note that there is no inverse relationship from IdTag to Animal or Inventory, and let's assume the RfidTag.code is unique. I read Retrieving Polymorphic Hibernate Objects Using a Criteria Query and Hibernate polymorphic query but these discussions does not seem to answer my question.

public interface ItemWithIdTag
{
    IdTag getIdTag();
    void setIdTag(IdTag idTag);
}

@Entity public class Animal implements ItemWithIdTag,Serializable
{
    @Id @GeneratedValue(strategy=GenerationType.AUTO) private long id;

    @OneToOne(cascade = CascadeType.ALL)
    private IdTag idTag;
}

@Entity public class Inventory implements ItemWithIdTag,Serializable
{
    @Id @GeneratedValue(strategy=GenerationType.AUTO) private long id;

    @OneToOne(cascade = CascadeType.ALL)
    private IdTag idTag;
}

@Entity @Table(name = "IdTag") @Inheritance(strategy= InheritanceType.JOINED)
public class IdTag implements Serializable
{
    @Id @GeneratedValue(strategy=GenerationType.AUTO) private long id;
    private Date created;
}

@Entity @Table(name = "RfidTag")
public class RfidTag extends IdTag implements Serializable
{
    private String code;
}

现在我要查询 Animal RfidTag.code 的c $ c>或库存，如 Animal ejb = bean。 fEntityWithRfidTag（Animal.class，myRfIdCode）;

Now I want to query either Animal or Inventory for a given RfidTag.code like Animal ejb = bean.fEntityWithRfidTag(Animal.class,"myRfIdCode");

public <T extends ItemWithIdTag> T fOwner(Class<T> type, String catName)
{
    CriteriaBuilder criteriaBuilder = em.getCriteriaBuilder();
    CriteriaQuery<T> criteriaQuery = criteriaBuilder.createQuery(type);
    Root<T> from = criteriaQuery.from(type);

    Path<Object> path = from.join("idTag").get("code");

    CriteriaQuery<T> select = criteriaQuery.select(from);
    select.where(criteriaBuilder.equal(path, catName));

    TypedQuery<T> q = em.createQuery(select); 
    T result = (T)q.getSingleResult();}
    return result;
}

不幸的是我得到以下错误：

Unfortuately I get the following errror:

javax.ejb.EJBException: java.lang.IllegalArgumentException:
Unable to resolve attribute [code] against path [null]

我认为这与继承有关 IdTag - > RfidTag 和 Animal 只知道 IdTag 而不是 RfidTag.code 。这样的查询是否可能？

I assume that this is related to the inheritance IdTag -> RfidTag and Animal only knows about IdTag and not the RfidTag.code. Are queries like this possible?

推荐答案

如果您使用的是EclipseLink，解决方案很简单。修改路径条件以转换为RfIdTag：

If you are using EclipseLink, solution is simple. Modify the Path criteria to cast to RfIdTag:

Path<Object> path = ((Path) from.join("idTag").as(RfIdTag.class)).get("code");

如果您使用的是Hibernate，请将您的方法替换为：

If you are using Hibernate, replace your method with:

public static <T extends ItemWithIdTag> T fOwner(Class<T> type, String catName) {
    CriteriaBuilder criteriaBuilder = em.getCriteriaBuilder();
    CriteriaQuery<T> criteriaQuery = criteriaBuilder.createQuery(type);
    Root<T> fromType = criteriaQuery.from(type);
    Root<RfIdTag> fromRfId = criteriaQuery.from(RfIdTag.class);

    Path<Object> pathCode = fromRfId.get("code");
    Path<Object> pathIdTagType = fromType.get("idTag");
    Path<Object> pathIdTagRfId = fromRfId.get("id");

    CriteriaQuery<T> select = criteriaQuery.select(fromType);
    select.where(
            criteriaBuilder.equal(pathCode, catName),
            criteriaBuilder.equal(pathIdTagType, pathIdTagRfId));

    TypedQuery<T> q = em.createQuery(select);
    return q.getSingleResult();
}

这使得加入（过滤后的笛卡儿产品）介于 T和RfIdTag。

This makes a "join" ("a filtered cartesian product") between "T" and "RfIdTag".

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