{
    "student_name": '',
    "student_id": '',
    "student_record": [
        {
          "sub_1": "xx",
          "sub_2": "xxx",
          "sub_3": "xxxx xxx",
          "sub_4": "xx/xx/xx,
          "sub_5": "XXX",
        },
         {
          "sub_1": "xx",
          "sub_2": "xxx",
          "sub_3": "xxxx xxx",
          "sub_4": "xx/xx/xx,
          "sub_5": "XXX",
        }
      ]
  }

class StudentRecord(db.Document):
    sub_1 = db.StringField()
    sub_2 = db.StringField()
    sub_3 = db.StringField()
    sub_4 = db.StringField()
    sub_4 = db.StringField()

class StudentDetails(db.Document):
    student_name = db.StringField()
    student_id = db.StringField()
    sudent_record = DocumentField(StudentRecord)