conversion sql query to jpa

Question

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

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

Join employee = root.join("employees", JoinType.LEFT);

Expression 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 query = em.createQuery(criteria);