Update/Iterate over embedded Array MongoDB

Question

I have a document structure like so:

{   
  data: null,
  subArray: [{
    key: 'a',
    subData: [] 
  }, {
    key: 'b',
    subData: []
  }] 
}

I will receive an array containing subArray keys, like: `['a', 'b']

I want to iterate over the subArray to push a value to subData, so that when subArray is ['a','b'], my data will now be like:

{   
  data: null,
  subArray: [{
    key: 'a',
    subData: ['dataToPush'] 
  }, {
    key: 'b',
    subData: ['dataToPush']
  }] 
}

I have this query to do that:

update({_id:"...", "subArray.key":{"$in":['a','b']},
       {'$addToSet':{'subArray.$.subData':'...'}}})

Thinking that $in will let me loop through my subArray. But I realize this does not work because $in gets the elements that match the elements in the array, so I will get my data but not iterate over my subArray.

Is it possible to complete this with a specific selector/modifier combo?

wdberkeley · Accepted Answer · 2014-12-24 20:55:27Z

1

No, not with multiple keys. For one key "a", you could use a query like

db.test.update({ "subArray.key" : "a" }, { "$push" : { "subArray.$.subData" : "dataToPush" } })

but the $ positional operator can only be used for a single match in one update. You could do one update like the above per key, or retrieve the document, modify it based on all of the keys, then save over the original.

answered Dec 24, 2014 at 20:55

wdberkeley

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