在一对多关系中指定子表的标准 [英] Specifying criteria for child table in One To Many Relationship

问题描述

我有两个具有一对多关系的实体对象（A和B）。我正在使用JPA（Hibernate）来连接这些表并查询它们以获取特定的结果集，但是在获取我的结果时不会应用我为子表（B）指定的条件。这是我定义查询的方式：

  CriteriaBuilder builder = entityManager.getCriteriaBuilder（）; 
 CriteriaQuery< A> query = builder.createQuery（A.class）; 
 Root< A> a = query.from（A.class）; 
加入< A，B> abJoined = a.join（A_.b）; 
 
 query.distinct（true）
 .where（builder.and（
 builder.equal（a.get（A_.id），id），
 builder .equal（a.get（A_.active），1），
 builder.equal（a.get（A_.location），1011），
 builder.equal（a.get（A_.status ），待定），
 
 builder.equal（abJoined.get（B_.status），Not Moved），
 builder.greaterThan（abJoined.get（B_.detailId） ，0）
））; 
  

当我调用 entityManager.createQuery（query）.getResultList（）; 我得到实体'A'的一个实例，但是当我尝试通过'A' a.getB（）访问'B'时，两个标准我为 abJoined 指定的所有实例都未应用，并且我获得了连接到'A'的'B'的所有实例。我还需要做些什么来获得这些标准？如果不能应用标准，是否有推荐的方法从结果集中删除'B'的相应实例？

我可以提供更多代码或其他详细信息if必要的。

解决方案

查询用于选择查询必须返回哪个实体。但是A实体永远不会是仅包含其子集的子集的部分实体。它们将始终是A的完整实例，反映A在数据库中的状态，以及与A有关的B。

顺便说一句，即使这是可能的（这不是，并且明确地被JPA规范禁止），你的查询至少需要加载Bs以及使用fetch连接。否则，只有A的状态被查询返回，并且链接的Bs会被延迟加载。

I have two entity objects (A and B) that have a One-To-Many relationship. I am using JPA (Hibernate) to join these tables and query them for a specific result set, but the criteria I specify for the child table (B) are not applied when fetching my results. This is how I have defined the query:

CriteriaBuilder builder = entityManager.getCriteriaBuilder();
CriteriaQuery<A> query = builder.createQuery(A.class);
Root<A> a = query.from(A.class);
Join<A, B> abJoined = a.join(A_.b);

query.distinct(true)
    .where(builder.and(
        builder.equal(a.get(A_.id), id),
        builder.equal(a.get(A_.active), 1),
        builder.equal(a.get(A_.location), 1011),
        builder.equal(a.get(A_.status), "Pending"),

        builder.equal(abJoined.get(B_.status), "Not Moved"),
        builder.greaterThan(abJoined.get(B_.detailId), 0)
    ));

When I call entityManager.createQuery(query).getResultList(); I get one instance of entity 'A', but when I try to access 'B' through 'A' a.getB() the two criteria that I had specified for abJoined are not applied and I get all instances of 'B' that are joined to 'A'. Is there something more I need to do to get these criteria applied? If the criteria cannot be applied, is there a recommended method for removing the corresponding instances of 'B' from the result set?

I can provide more code or other details if necessary.

解决方案

The query is used to select which A entities must be returned by the query. But the A entities will never be partial entities containing only a subset of their Bs. They will always be complete instances of A, reflecting the state of what A is in the database, and which B this A is related to.

BTW, even if this was possible (it's not, and explicitely forbidden by the JPA spec), your query would at least have to load the Bs as well, using a fetch join. Otherwise only the state of A is returned by the query, and the linked Bs are loaded lazily.

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