Question

我有一个Employee的表和一个Meeting变量（我也有一个会议表）。 Meeting和Employee之间的关系是many-to-many。是否可以编写一个JPA Query，它从数据库中获取附加到Meeting变量的所有Employees。如果是这样，查询是什么？另一个选择是获取所有Employees并查看哪些不在Meeting变量中，但可能很慢。任何想法我该怎么办？

Answer 1

例如，这是您的员工实体：

@Entity
public class Employee  {

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

查询：从附加到的数据库中获取所有员工会议变量

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

查询：获取所有员工，并查看哪些员工不在会议中变量

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

查询获取未附加到特定变量的数据 - JPA

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