conversion sql query to jpa

问题

I have a query

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

and how i can convert this to jpa right now i have:

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);

I simplified both examples by removing ordering and grouping can anyone tell me how i can modifie my jpa code to get same reslults like from my sql query

thanks in advance

回答1:

You're not far from the result. The problem is that, AFAIK, you can't add any restriction on the on clause, using JPA. So the query wil have to be rewritten as

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)

Here is the equivalent of this query not tested):

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);

来源：https://stackoverflow.com/questions/7848582/conversion-sql-query-to-jpa

标签

jpa-2.0