使用 JPA 2.1，我如何将本机查询结果映射到 @Transient 字段（taht is a Set）？

Posted 2023-04-14

【中文标题】使用 JPA 2.1，我如何将本机查询结果映射到 @Transient 字段（taht is a Set）？

【英文标题】：Using JPA 2.1, how do I map a native query result to a @Transient field taht is a Set?

【发布时间】：2015-04-10 20:06:03

【问题描述】：

我正在使用 JPA 2.1、Hibernate 4.1.3.Final 和 mysql 5.5.37。如何将结果集映射到 @Transient 集合？在我的实体中，我已经设置了

@Entity
@Table(name = "category", uniqueConstraints =  @UniqueConstraint(columnNames =  "NAME", "PD_ONLY" ) )
@SqlResultSetMapping(name = "categoryResults", classes =  @ConstructorResult(targetClass = org.mainco.subco.core.domain.Category.class, columns = 
        @ColumnResult(name = "id"), @ColumnResult(name = "name"), @ColumnResult(name = "pd_only"),
        @ColumnResult(name = "subjects") ) )
public class Category implements Serializable, Comparable<Category>


    @Id
    @Column(name = "ID")
    @GeneratedValue(generator = "uuid-strategy")
    private String id;

    private String name;

    @Column(name = "PD_ONLY")
    private Boolean pdOnly;

    @Transient
    private Set<Subject> subjects;

然后我尝试使用本机查询来映射事物……

final Query q = m_entityManager.createNativeQuery(
                                   "select distinct c.id, " + 
                                   "                c.name, " + 
                                   "                c.pd_only, " + 
                                   "                e.subject_id FROM category c, " + 
                                   "                                  resource_category rc, " + 
                                   "                                  product_resource pr, " + 
                                   "                                  product p, " + 
                                   "                                  product_ebook pe, " + 
                                   "                                  book e where c.pd_only = :pdOnly and c.id = rc.category_id and rc.resource_id = pr.resource_id and pr.product_id = p.id and p.id = pe.product_id and pe.ebook_id = e.id and c.id = 'Curriculum Maps';",
                                   "categoryResults")
                                   .setParameter("pdOnly", pdOnly ? "1" : "0");
    return q.getResultList();

但我得到以下异常......

javax.persistence.PersistenceException: org.hibernate.HibernateException: Could not resolve column name in result set [subjects]
    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1074)
    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:988)
    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:974)
    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:919)
    at com.mysql.jdbc.ResultSetImpl.findColumn(ResultSetImpl.java:1166)
    at org.hibernate.loader.custom.JdbcResultMetadata.resolveColumnPosition(JdbcResultMetadata.java:67)
    at org.hibernate.loader.custom.ScalarResultColumnProcessor.performDiscovery(ScalarResultColumnProcessor.java:59)
    at org.hibernate.loader.custom.ConstructorResultColumnProcessor.performDiscovery(ConstructorResultColumnProcessor.java:58)
    at org.hibernate.loader.custom.CustomLoader.autoDiscoverTypes(CustomLoader.java:498)
    at org.hibernate.loader.Loader.getResultSet(Loader.java:2073)
    at org.hibernate.loader.Loader.executeQueryStatement(Loader.java:1862)
    at org.hibernate.loader.Loader.executeQueryStatement(Loader.java:1838)
    at org.hibernate.loader.Loader.doQuery(Loader.java:909)
    at org.hibernate.loader.Loader.doQueryAndInitializeNonLazyCollections(Loader.java:354)
    at org.hibernate.loader.Loader.doList(Loader.java:2553)
    at org.hibernate.loader.Loader.doList(Loader.java:2539)
    at org.hibernate.loader.Loader.listIgnoreQueryCache(Loader.java:2369)
    at org.hibernate.loader.Loader.list(Loader.java:2364)
    at org.hibernate.loader.custom.CustomLoader.list(CustomLoader.java:353)
    at org.hibernate.internal.SessionImpl.listCustomQuery(SessionImpl.java:1873)
    at org.hibernate.internal.AbstractSessionImpl.list(AbstractSessionImpl.java:311)
    at org.hibernate.internal.SQLQueryImpl.list(SQLQueryImpl.java:141)
    at org.hibernate.jpa.internal.QueryImpl.list(QueryImpl.java:573)
    at org.hibernate.jpa.internal.QueryImpl.getResultList(QueryImpl.java:449)
    at org.mainco.subco.core.repo.CategoryDaoImpl.findCategories(CategoryDaoImpl.java:78)
    at org.mainco.subco.core.repo.CategoryDaoImpl.findNonPDCategories(CategoryDaoImpl.java:38)
    at org.mainco.subco.core.repo.CategoryDaoIT.testFindNonPDCategories(CategoryDaoIT.java:30)

关于如何将从我的本机查询返回的内容映射到结果集中的任何想法？我也愿意不使用原生 SQL 并使用 CriteriaBuilder/JPQL 做一些事情。

【问题讨论】：

您认为如何将一行数据映射到一个集合？每行只有一个“subject_id”，所以您希望每个集合中有 1 个元素？

这就是我问这个问题的原因！我想知道怎么做。

【参考方案1】：

您可以将结果列表作为 Object[] 的原始列表。然后，您可以根据需要投射对象并安装实例。

参见下面的代码 sn-p。我没有测试过代码，所以如果你可以尝试一下，请告诉我们结果。

// Here you get the result set as a raw list of objects
@SuppressWarnings("unchecked")
List<Object[]> resultList = nq.getResultList();

// Maybe you will need a set of Category for the "categoryResults"
Set<Category> categoryResults = new HashSet<>();

// Here you cast the whole result set
for (Object[] record : resultList) 
    // Sets Category
    Category category = new Category();
    category.setId((Integer) record[0]);
    category.setName((String) record[1]);
    category.setPdOnly((Boolean) record[2]);

    // Sets Subject
    Subject subject = new subject();
    subject.setId((Integer) record[3]);

    // Adds Subject to the HashSet
    Set<Subject> subjectsSet = new HashSet<>();
    subjectsSet.add(subject);

    // Here you have what you need, the setting of the transient field
    category.setSubjects(subjectsSet);

    // Finally adds category onto results
    categoryResults.add(category);