Mongodb findAndUpdate $unset a field with an empty array

This is my example document:

{
  keys: {
    attr1: ['a', 'b', 'c'],
    attr2: ['d', 'e']
  }
}

I remove the items in the array like this...

{
  $pullAll: {
    'keys.attr2': ['d', 'e']
  }
}

And this leaves me with an empty array for the attr2 field:

{
  keys: {
    attr1: ['a', 'b', 'c'],
    attr2: []
  }
}

But what I want to do is if the field is now an empty then I want $unset that field so that the final result looks like this:

{
  keys: {
    attr1: ['a', 'b', 'c']
  }
}

I want to do this within a single find and update operation.

Thanks for the help.

Unfortunately that isn't possible. You can't perform an additional match at the same time that you're performing the update operations. You can, however, perform a second update that matches an empty array and then unsets the field.

It's just a limitation that you're going to have to work around.