JPA 本机查询选择和转换对象 [英] JPA Native Query select and cast object

问题描述

我有一个扩展 User 的对象 Admin.默认情况下，两个对象都在我的 Derby 数据库的表 User_ 中(包括来自 Admin 的字段).通常我会像这样选择一个 User:

I have got an Object Admin which extends User. By default both Objects are in the table User_ of my Derby Database (included fields from Admin). Normally I'd select an User like this:

CriteriaBuilder cb = em.getCriteriaBuilder();
CriteriaQuery<User> query = cb.createQuery(User.class);
Root user= query.from(User.class);
Predicate predicateId = cb.equal(category.get("id"), id);
query.select(user).where(predicateId);
return em.createQuery(query).getSingleResult();

但是，由于我的查询的复杂性，我使用的是这样的本机查询:

However due to the complexity of my query I'm using a native query like this:

Query query = em.createNativeQuery("SELECT USER.* FROM USER_ AS USER WHERE ID = ?");
query.setParameter(1, id);
return (User) query.getSingleResult();

虽然这会抛出一个强制转换异常.我认为这是由于 Admin 中的任何字段造成的.

Though this throws a cast exception. I figure this is due to any fields from Admin.

我的问题是，如何使用与第一个示例相同结果的本机查询选择 User(包括 @LOB 和 的相同值)>@ManyToOne(等等)作为 JPQL 查询将返回)?

My question is, how can I select a User using a native query with an equal result as the first example (including the same values for @LOB and @ManyToOne (et cetera) as the JPQL query would return)?

推荐答案

您可能想尝试以下方法之一:

You might want to try one of the following ways:

• 使用方法createNativeQuery(sqlString, resultClass)

  也可以使用 EntityManager.createNativeQuery() API 动态定义原生查询.

• Using the method createNativeQuery(sqlString, resultClass)

  Native queries can also be defined dynamically using the EntityManager.createNativeQuery() API.

String sql = "SELECT USER.* FROM USER_ AS USER WHERE ID = ?";

Query query = em.createNativeQuery(sql, User.class);
query.setParameter(1, id);
User user = (User) query.getSingleResult();

使用注解@NamedNativeQuery

原生查询通过@NamedNativeQuery 和@NamedNativeQueries 定义注释，或 XML 元素.

Using the annotation @NamedNativeQuery

Native queries are defined through the @NamedNativeQuery and @NamedNativeQueries annotations, or <named-native-query> XML element.

@NamedNativeQuery(
    name="complexQuery",
    query="SELECT USER.* FROM USER_ AS USER WHERE ID = ?",
    resultClass=User.class
)
public class User { ... }

Query query = em.createNamedQuery("complexQuery", User.class);
query.setParameter(1, id);
User user = (User) query.getSingleResult();

您可以在优秀的公开书Java Persistence中阅读更多内容(可在 PDF).

You can read more in the excellent open book Java Persistence (available in PDF).

^{─────────
注意:关于 getSingleResult() 的使用，请参见 为什么你不应该在 JPA 中使用 getSingleResult().}

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