Can you specify a key for $addToSet in Mongo?

Question

I have a document:

{ 'profile_set' :
  [
    { 'name' : 'nick', 'options' : 0 },
    { 'name' : 'joe',  'options' : 2 },
    { 'name' : 'burt', 'options' : 1 }
  ] 
}

and would like to add a new document to the profile_set set if the name doesn't already exist (regardless of the option).

So in this example if I tried to add:

{'name' : 'matt', 'options' : 0}

it should add it, but adding

{'name' : 'nick', 'options' : 2}

should do nothing because a document already exists with name nick even though the option is different.

Mongo seems to match against the whole element and I end up with to check if it's the same and I end up with

profile_set containing [{'name' : 'nick', 'options' : 0}, {'name' : 'nick', 'options' : 2}]

Is there a way to do this with $addToSet or do I have to push another command?

Answer 1

You can qualify your update with a query object that prevents the update if the name is already present in profile_set. In the shell:

db.coll.update(
    {_id: id, 'profile_set.name': {$ne: 'nick'}}, 
    {$push: {profile_set: {'name': 'nick', 'options': 2}}})

So this will only perform the $push for a doc with a matching _id and where there isn't a profile_set element where name is 'nick'.

Answer 2

As of MongoDB 4.2 there is a way to do this using aggregation expressions in update.

For your example case, you would do this:

newSubDocs = [ {'name' : 'matt', 'options' : 0}, {'name' : 'nick', 'options' : 2} ];
db.coll.update( { _id:1 },
[ 
   {$set:  { profile_set:  {$concatArrays: [ 
      "$profile_set",  
      {$filter: {
             input:newSubDocs, 
             cond: {$not: {$in: [ "$$this.name", "$profile_set.name" ]}} 
      }}
   ]}}}
])