Can you specify a key for $addToSet in Mongo?

问题

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?

回答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'.

来源：https://stackoverflow.com/questions/55052488/dictionary-inside-dictionary-insertion-in-mongodb