查询获取未附加到特定变量的数据 - JPA

Question

我有一个 table 的 Employee 和一个 Meeting 变量（我还有一个 table 用于会议）。 Meeting 和 Employee 之间的关系是 many-to-many。是否可以编写一个 JPA 查询，从数据库中获取所有附加到 Meeting 变量的员工。如果是这样，查询是什么？另一种选择是获取所有 Employees 并查看哪些不在 Meeting 变量中，但可能很慢。有什么想法我该怎么做？

Answer 1

例如，这是您的员工实体：

@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

查询获取未附加到特定变量的数据 - JPA

Query for getting data not attached to a particular variable - JPA

java

database

many-to-many

jpa