java JPA Criteria API：如何在嵌套集合中选择属性
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JPA Criteria API: How to select property in nested collection
提问by Otávio Garcia
I have a class Customerand CustomerDependantentities. Customerhas many to many bi-directional relationship with its dependents. I need to find customers filtering by name and dependent name.
我有一个类Customer和CustomerDependant实体。Customer与其依赖项具有多对多的双向关系。我需要查找按名称和相关名称过滤的客户。
It's done something like this in JPQL:
它在 JPQL 中做了这样的事情：
select c join fetch c.dependants d from Customer c where c.name like
'foo' and d.name like 'foo'
How I can do the same thing with JPA Criteria Queries?
我如何使用 JPA Criteria Queries 做同样的事情？
回答by Edwin Dalorzo
Taken from JPA Specification section 6.5.4
取自 JPA 规范第 6.5.4 节
CriteriaQuery<Department> q = cb.createQuery(Department.class);
Root<Department> d = q.from(Department.class);
d.fetch(Department_.employees, JoinType.LEFT);
q.where(cb.equal(d.get(Department_.deptno), 1)).select(d);
This query is equivalent to the following Java Persistence query language query:
此查询等效于以下 Java Persistence 查询语言查询：
SELECT d
FROM Department d LEFT JOIN FETCH d.employees
WHERE d.deptno = 1
This is what I do it without fetch
这就是我在没有获取的情况下所做的
CriteriaQuery<Department> q = cb.createQuery(Department.class);
Root<Department> dept = q.from(Department.class);
Join<Department,Employee> emp = d.join(Department_.employees);
q.where(cb.equal(emp.get(Employee_.name),"edalorzo"));
Fetch is a type of join, so I guess you could experiment with that too.
Fetch 是一种连接，所以我想你也可以尝试一下。
