mongoDB $pull from subarray

Question

Maybe this is a popular question but I didn't manage to find my solution. I have a collection with elements like the following:

_id: ObjectId("52821d6c21c495b30a000015")
structure: {
  elements: [{
    id: "non-unique-id1",
    other_data: "value"
    subs: [{
      id: 1,
      field1: "somevalue",
      field2: "other value"
    }, {
      id: 2,
      field1: "somevalue",
      field2: "other value"
    }, {
      id: 3,
      field1: "somevalue",
      field2: "other value"
    }]
  }, {
    id: "non-unique-id2",
    subs: [{
      id: 1,
      field1: "somevalue",
      field2: "other value"
    }, {
      id: 2,
      field1: "somevalue",
      field2: "other value"
    }, {
      id: 3,
      field1: "somevalue",
      field2: "other value"
    }]
  }]
}

Now I would like to remove an element from the subs subarray given it's id. I'd like the remove to happen on all element fields.

I tried the following, but even though I get no error, nothing happens:

db.objects.update({
  "_id" : ObjectId("52821d6c21c495b30a000015")
},{
  $pull: {
    "structure.elements.subs": {id: 2}
  }
})

This should have removed the 2 occurrences of the hash with id: 2

Tried $pullAll as well but I'm getting an error:

Modifier $pushAll/pullAll allowed for arrays only

Any ideas on how can I achieve my goal?

JohnnyHK · Accepted Answer · 2013-12-05 13:42:09Z

3

Mongo's support for updating nested arrays is pretty weak. You have to target each elements array element separately in your $pull:

db.objects.update({
  "_id" : ObjectId("52821d6c21c495b30a000015")
},{
  $pull: {
    "structure.elements.0.subs": {id: 2},
    "structure.elements.1.subs": {id: 2}
  }
})

answered Dec 5, 2013 at 13:42

JohnnyHK

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1 Comment

Oktav Over a year ago

Hmm, I was afraid of that... Unfortunately the elements array is not ordered nor fixed so I wouldn't know what indexes to target. Thanks anyway.

Anthonny · Accepted Answer · 2013-12-05 14:29:13Z

1

You can use $, but the query will only delete 1 subs, for the two subs of your example you must run update twice. You'll need to write a script to iterate on your docs.

db.objects.update({
  "_id" : ObjectId("52821d6c21c495b30a000015"),
  "structure.elements.subs.id": 2
},{
  $pull: {
    "structure.elements.$.subs": {"id": 2}
  }
});

If your need is for a temporary administration action it's ok, but for an application performance will too bad

Sorry for my poor english :)

answered Dec 5, 2013 at 14:29

Anthonny

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