Java Mongo查询另一个嵌套对象中的嵌套对象

我对MongoDb数据库的员工、部门和主题有几个类，关系如下

public class Employee {
 @Id
 private long id;
 private String name;
 @DBRef
 private Subject subject;
} 

public class subject{
 @Id 
 private long id;
 private String name;
 @DBRef
 private Department department;
}

public class Department{
 @Id     
 private long id;
 private String name;
}

我可以使用主题Id查询员工

db.employee.find("subject.$id":<subjectId>)

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提前感谢

您能否共享MongoDB中显示的一些对象，即Json？如果您使用的是Mongo3.2，那么您有内置的连接操作-但是您确定您的数据模型非常适合MongoDB吗？在Mongo中，通常最好将数据建模为非规范化文档，这样就不需要连接。

db.employee.find("subject.department.$id":<departmentId>)

Employee ::

{"_id": 1,"name":"student1","subject":{"$ref":"subject","$id":1}}
{"_id": 2,"name":"student2","subject":{"$ref":"subject","$id":2}}
{"_id": 3,"name":"student3","subject":{"$ref":"subject","$id":3}}

Subject ::
{"_id": 1,"name":"subject1","department":{"$ref":"department","$id":1}}
{"_id": 2,"name":"subject2","department":{"$ref":"department","$id":1}}
{"_id": 3,"name":"subject3","department":{"$ref":"department","$id":2}}

Department ::

{"_id": 1,"name":"department1"}
{"_id": 2,"name":"department2"}