jpa-2.0 - 将sql查询转换为jpa

Question

我有一个疑问

SELECT d.name, count(e.id) FROM department d LEFT OUTER JOIN employee e on e.department_id = d.id and e.salary > 5000

以及如何将其转换为 jpa 现在我有:

CriteriaQuery<Object[]> criteria = builder.createQuery(Object[].class); 
Root<Department> root = criteria.from(Department.class);
Path<String> name = root.get("name");
Expression<Long> empCount = builder.count(root.get("employees").get("id"));
criteria.multiselect(name,empCount);
TypedQuery<Object[]> query = em.createQuery(criteria);

我通过删除排序和分组来简化这两个示例 谁能告诉我如何修改我的 jpa 代码以获得与 sql 查询相同的结果

提前致谢

Answer 1

你离结果不远了。问题是，据我所知，您无法使用 JPA 对 on 子句添加任何限制。因此查询必须重写为

SELECT d.name, count(e.id) FROM department d 
LEFT OUTER JOIN employee e on e.department_id = d.id 
where (e.id is null or e.salary > 5000)

这是与此查询等效的未测试的查询):

CriteriaQuery<Object[]> criteria = builder.createQuery(Object[].class); 
Root<Department> root = criteria.from(Department.class);
Path<String> name = root.get("name");

Join<Department, Employee> employee = root.join("employees", JoinType.LEFT);

Expression<Long> empCount = builder.count(employee.get("id"));
criteria.multiselect(name,empCount);
criteria.where(builder.or(builder.isNull(employee.get("id")),
                          builder.gt(employee.get("salary"), 5000)));

TypedQuery<Object[]> query = em.createQuery(criteria);