Question

Given the following MongoDB example collection (“schools”), how do you remove student “111” from all clubs?

[
  {
    "name": "P.S. 321",
    "structure": {
      "principal": "Fibber McGee",
      "vicePrincipal": "Molly McGee",
      "clubs": [
        {
          "name": "Chess",
          "students": [
            ObjectId("111"),
            ObjectId("222"),
            ObjectId("333")
          ]
        },
        {
          "name": "Cricket",
          "students": [
            ObjectId("111"),
            ObjectId("444")
          ]
        }
      ]
    }
  },
  ...
]

I’m hoping there’s some way other than using cursors to loop over every school, then every club, then every student ID in the club…

Answer 1

MongoDB doesn’t have a great support for arrays within arrays (within arrays …). The simplest solution I see is to read the whole document into your app, modify it there and then save. This way, of course, the operation is not atomic, but for your app it might be ok.