java - Hibernate选择子对象进入界面

Question

为了仅收集我需要的数据，我使用以下查询来进行对象声明:

        @Query(value = "select d.id as id "
            + " , d.statusChanged as statusChanged "
            + " from Declaration d ", 
            countQuery="select count(id) from Declaration")
    Page<DeclarationIDTO> findAllDeclarationListIDTO(Pageable pageable);

DeclarationIDTO 有一个 getId() 和一个 getStatusChanged()。

这有效。

现在我想添加自由职业者的 ID，如下所示:

    @Query(value = "select d.id as id "
            + " , d.statusChanged as statusChanged "
            + " , f.id as 'freelancer.id' "
            + " from Declaration d join d.freelancer f", 
            countQuery="select count(id) from Declaration")
    Page<DeclarationIDTO> findAllDeclarationListIDTO(Pageable pageable);

DeclarationIDTO 有一个 getFreelancer() ，它有一个 getId() 但我收到错误:

Caused by: org.hibernate.hql.internal.ast.QuerySyntaxException: expecting IDENT, found ''freelancer.id'' near line 1, column 66 [select d.id as id  , d.statusChanged as statusChanged  , f.id as 'freelancer.id'  from nl.tibi.sbys.domain.Declaration d join d.freelancer f]

知道如何使用对象链吗？

可能的解决方法:

1)扁平化界面:

@Query(value = "select d.id as id "
        + " , d.statusChanged as statusChanged "
        + " , f.id as 'freelancer_id' "
        + " from Declaration d join d.freelancer f", 
        countQuery="select count(id) from Declaration")
Page<DeclarationIDTO> findAllDeclarationListIDTO(Pageable pageable);

DeclarationIDTO 将具有 getId()、getStatusChanged() 和 getFreelancer_id()

缺点是界面必须复制所有需要的自由职业者字段，并且我必须使用映射器将 freelancer_id 映射到具有 freelancer.id 的 DTO 对象

2)使用构造函数而不是接口(interface):

@Query(value = "select new DeclarationDTO(d.id "
        + " , d.statusChanged "
        + " , f.id) "
        + " from Declaration d join d.freelancer f", 
        countQuery="select count(id) from Declaration")
Page<DeclarationDTO> findAllDeclarationListIDTO(Pageable pageable);

缺点是我需要为不同的页面提供许多构造函数，或者需要选择空值来扰乱我的查询

3)每个对象多个查询，这会影响性能并且需要大量工作。

4) 选择完整的子对象:

@Query(value = "select d.id as id "
    + " , d.statusChanged as statusChanged "
    + " , f as freelancer "
    + " from Declaration d join d.freelancer f", 
    countQuery="select count(id) from Declaration")

Page findAllDeclarationListIDTO(Pageable pageable);

DeclarationIDTO 有一个 getId() getStatusChanged() 和 getFreelancer()

这项工作仍然收集了许多数据，这对性能来说是一个缺点。

如果有一个简单的解决方案来获取 f.id，它将解决所有缺点。

这里似乎有一个答案:

https://docs.spring.io/spring-data/jpa/docs/current/reference/html/#projections

什么时候我会调查它。

Answer 1

1) 您的 DeclarationIDTO 必须具有按顺序包含 id 和 statusChange 参数的构造函数

2) 尝试在查询中添加具有完全限定名称的新运算符:

"select new my.package.DeclarationIDTO(d.id as id, d.statusChanged as statusChanged "
    + " , f.id as 'freelancer.id' "
    + " from Declaration d join d.freelancer f",