JPA CriteriaBuilder

JPA CriteriaBuilder

假设实体客户具有如下

OneToMany

属性：

@oneToMany(mappedBy = "customerId")private Collection<Order> orders;

您可以使用以下查询：

EntityManager em;  // to be built or injectedCriteriaBuilder cb = em.getCriteriaBuilder();CriteriaQuery<Tuple> cq = cb.createTupleQuery();Root<Customer> customer = cq.from(Customer.class);CollectionJoin<Customer, Order> orders = customer.join(Customer_.orders, JoinType.LEFT);cq.select(cb.tuple(customer, cb.count(orders)));cq.where(... add some predicates here ...);cq.groupBy(customer.get(Customer_.id));cq.orderBy(cb.desc(cb.count(orders)));List<Tuple> result = em.createQuery(cq).getResultList();for (Tuple t : result) {    Customer c = (Customer) t.get(0);    Long cnt = (Long) t.get(1);    System.out.println("Customer " + c.getName() + " has " + cnt + " orders");}

上面的方法使用metamodel。如果你不喜欢它，你可以替换

Customer_.orders

使用

"orders"

，并

Customer_.id

用

"id"

。

如果

OneToMany

财产是另一种类型的，更换

CollectionJoin

用正确类型的集合（

ListJoin

，

SetJoin

，

MapJoin

）。