这两天学习MongoDB，正在尝试聚合三个集合但无法实现以下是数据库中维护的四个集合大学{"_id":"5834ecf7432d92675bde9d82","name":"NIFT"}大学{"_id":"5834ecf7432d92675bde9d83","name":"NIFTHyderabad","university_id":"5834ecf7432d92675bde9d82"}部门{"_id":"5834ecf7432d92675bde9d84","department_name":"FashionTechnology","college_id":"5834ecf7432d92

这两天学习MongoDB，正在尝试聚合三个集合但无法实现以下是数据库中维护的四个集合大学{"_id":"5834ecf7432d92675bde9d82","name":"NIFT"}大学{"_id":"5834ecf7432d92675bde9d83","name":"NIFTHyderabad","university_id":"5834ecf7432d92675bde9d82"}部门{"_id":"5834ecf7432d92675bde9d84","department_name":"FashionTechnology","college_id":"5834ecf7432d92