休眠查询（或条件）：在Where子句中使用Count

Question

I have 1 class following:

public Class Customer{
  @id
  int id;
  @ManyToOne(fetch = FetchType.LAZY)
  @JoinColumn(name = "ParentID")
  Customer parentId
}

How can I select all Customer which have total Children less more than 2?

Answer 1

Use following type of query. This is only for reference. Make changes in code according to your requirement.

select Customer.customerId , count(Customer.children)
from Customer
group by Customer.customerId
having count(Customer.children)  > 2

I am assuming you'll add childrens using @OneToMany relationship.

Answer 2

You can group by the parent entity filtering according the amount of associated customers

SELECT p 
FROM Customer c JOIN c.parentId p 
GROUP BY p 
HAVING COUNT(c) > 2

Please check if having condition is what you want.

This query should be supported if the Hibernate version fully implements the JPA Specification (in JPA 2.1 specs see section 4.7).

I am not sure if Hibernate allows to do that. If you suffer any trouble, consider what says in HH - The group by clause and be aware about non-aggregated properties.