hibernate - JPQL 构造函数表达式 - org.hibernate.hql.ast.QuerySyntaxException :Table is not mapped

Question

我原来的问题是 https://stackoverflow.com/questions/12172614/hql-join-without-foreign-key-reference但找不到任何解决方案，因此使用 JPA 进行 native 查询。 entityManager 的 createNativeQuery 返回 Query 对象，该对象又返回 List<Object[]> .我不想在迭代列表时处理索引，因为它本质上很容易出错。因此，我查看了一些其他解决方案，并发现 JPQL 的构造函数表达式作为解决方案之一。

表结构是

Schema1 -TableA

 - NameColumn
 - PhoneColumn

对应的Java类是

    public class PersonSearch implements Serializable {

    public PersonSearch (String NameColumn, String PhoneColumn) {
        this.name = NameColumn;
        this.phone = PhoneColumn;
    }

    private String name;

    private String phone;

    public String getName() {
    return name;
    }

    public void setName(String name) {
    this.name = name;
    }

    public String getPhone() {
    return phone;
    }

    public void setPhone(String phone) {
    this.phone = phone;
    }
    }

查询是

 Select NEW com.xyz.PersonSearch(ms.NameColumn, ms.PhoneColumn) From Schema1.TableA ms Where ms.PhoneColumn='9134409930'

使用 entityManager API 运行此查询时

entityManager.createQuery(queryString, PersonSearch.class);

遇到错误。

Caused by: org.hibernate.hql.ast.QuerySyntaxException: Schema1.TableA is not mapped   [Select NEW com.xyz.PersonSearch(ms.NameColumn, ms.PhoneColumn) From Schema1.TableA ms Where ms.PHONE='9134409930']

我的代码有什么问题？有什么想法吗？

Answer 1

根据《Pro EJB 3 Java Persistence API》一书

构造函数表达式

A more powerful form of SELECT clause involving multiple expressions is the constructor expression, which specifies that the results of the query are to be stored using a user-specified object type. Consider the following query:

SELECT NEW example.EmployeeDetails(e.name, e.salary, e.department.name)
FROM Employee e

The result type of this query is the type example.EmployeeDetails. As the query processor iterates over the results of the query, it instantiates new instances of EmployeeDetails using the constructor that matches the expression types listed in the query. In this case the expression types are String, Double, and String, so the query engine will search for a constructor with those class types for arguments. Each row in the resulting query collection is therefore an instance of EmployeeDetails containing the employee name, salary, and department name.

The result object type must be referred to using the fully qualified name of the object. The class does not have to be mapped to the database in any way, however. Any class with a constructor compatible with the expressions listed in the SELECT clause can be used in a constructor expression.

Constructor expressions are powerful tools for constructing coarse-grained data transfer objects or view objects for use in other application tiers. Instead of manually constructing these objects, a single query can be used to gather together view objects ready for presentation on a web page.

示例代码如下

List result = em.createQuery("SELECT NEW example.EmpMenu(e.name, e.department.name) " +
         "FROM Project p JOIN p.employees e " +
         "WHERE p.name = ?1 " +
        "ORDER BY e.name").setParameter(1, projectName).getResultList();

EmpMenu 类是一个简单的 pojo，没有注释，但有正确的构造函数来匹配构造函数表达式。结果是返回的每一行的 EmpMenu 对象列表。

我相信您的 SQL 部分“....来自 Schema1.TableA ms ..”应该指的是映射的实体。因此，您应该将实体映射到 TableA，然后 jpql 应该更像“.... From MyTableAEntity ms ...”的内容，其中 MyTableAEntity 具有将其映射到 DB 表 TableA 的所有正确 jpa 注释。正如书摘所述，“SELECT NEW ...”的目标不必映射，但 FROM 子句中引用的实体可以。