Updating nested document in MongoDB

Question

I'm trying to update a hash that's nested in a MongDB document. I know about the $push function for arrays, and $set for completely overwriting elements, but I can't quite get the behaviour I'm looking for.

Here's what I'm trying to get:

Before:

{
  'id' => 1234,
  'evaluators' => {
    'A' => { 'x' => 2, 'y' => 4 },
  }
}

Expected, after:

{
  'id' => 1234,
  'evaluators' => {
    'A' => { 'x' => 2, 'y' => 4 },
    'B' => { 'x' => 3, 'y' => 5 },
  }
}

I've tried doing (in Ruby):

coll.update({ :id => id },
            { '$set' => {
                'evaluators' => {
                    evaluator_name => { 'adequacy' => adequacy, 
                                        'fluency'  => fluency }
                }
            } } )

But it overwrites the contents of my evaluators hash and I end up with:

{
  'id' => 1234,
  'evaluators' => {
    'B' => { 'x' => 3, 'y' => 5 },
  }
}

I could do a query to load the entire document into Ruby, change the data and re-insert it to the DB but I was wondering if there was a better way that I don't know about.

KL-7 · Accepted Answer · 2011-11-28 08:15:20Z

2

Try this one:

coll.update({ :id = > id }, { '$set' => {
    "evaluators.#{evaluator_name}" => {
        'adequacy' => adequacy, 'fluency' => fluency
    }
}})

answered Nov 28, 2011 at 8:15

KL-7

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