如何检索MongoDB中的子文档引用

Question

Data structure

"classrooms" : [
    {
        id : ObjectId("class1")
        "students" : [
            ObjectId("student1")
        ],
    },
    {
        id : ObjectId("class2")
        "students" : [
        ]
    }
],
"students" : [
    {
       "id" : ObjectId("student1"),
       "firstname" : "Ciljan",
       "age" : NumberInt(23)
    },
    {
       "id" : ObjectId("student2"),
       "firstname" : "John",
       "age" : NumberInt(19)
    }
]

The need

I have to provide a document where there are classrooms and students. Students could be assigned to a specific classroom, but not always, so a student could keep free. With the previous data structure, I have the subdocument " students " that provides the list of all the available students both assigned and not assigned. I can assign a student to a classroom storing the student id in the classrooms students array.

Problem

How can I retrieve these data in order to have for each classroom all the records about their assigned students?

Answer 1

Do you mean something like Classroom.find({}).populate('students') ? That'll return an array of Classrooms with the student fields populated.