java - 用于获取未附加到特定变量的数据的查询 - JPA

Question

我有一个Employee表和一个Meeting变量(我还有一个 session 表)。 Meeting 和 Employee 之间的关系是多对多。是否可以编写一个 JPA 查询来从数据库中获取附加到 session 变量的所有员工。如果是的话，查询是什么？另一种选择是获取所有员工并查看哪些不在 session 变量中，但可能会很慢。有什么想法我应该做什么吗？

Answer 1

例如，这是您的 Employee 实体:

@Entity
public class Employee  {

    @ManyToMany(mappedBy="employee")
    private List<Meeting> meetings;
    ...
}

Query: Get all the Employees from the database which are attached to the Meeting variable

SELECT e FROM Employee e WHERE :meeting MEMBER OF e.meetings

Query: Get all Employees and see which ones are not in the Meeting variable

SELECT e FROM Employee e WHERE :meeting NOT MEMBER OF e.meetings

示例代码:

String query = "SELECT e FROM Employee e WHERE :meeting MEMBER OF e.meetings";

Meeting meeting = new Meeting();
meeting.setId(1);

TypedQuery<Employee> query = em.createQuery(query, Employee.class);
List<Employee> employeesInMeeting = query.setParameter("meeting", meeting).getResultList();  
// this will select all employees that has a meeting with id=1 in their list