Why my document update in meteor method with $addToSet do nothing? - mongodb

Question

I want to develop a system where users can create topics and join topics created by other users. In my exemple, they are two user ("A" and "B"), the user "A" create a topic, and the user "B" join this topic.
When "A" create a topic (logged with "A"), I initialize like this :
topic.users = [{userId: this.userId, admin: 1}];
Topics.insert(topic);
Then, when i check mongo with Topics.find(), i have something which seems good:
{ "_id" : "8FDCyKssnrGxqvAep", "users" : [ { "userId" :"vQIMLMo5CK9YqxpTZ", "admin" : 1 } ] }
When "B" (logged with "B") join the topic i call:
Topics.update(topicId ,{ $addToSet: { users: { userId: this.userId, admin: 0 }} });
the update return "undefined", and i except, after the update, to have in my document something like:
{ "_id" : "8FDCyKssnrGxqvAep", , "users" : [ { "userId" :"vQIMLMo5CK9YqxpTZ", "admin" : 1 }, { "userId" :"AlsA4q
5PS5s5ts", "admin" : 0 } ] }
I have also try to do:
Topics.update({_id:topicId, 'users.userId': {$ne: this.userId}}, {$push: {users: { userId: this.userId, admin: 0 }}});
But when i check Mongo, i still have:
{ "_id" : "8FDCyKssnrGxqvAep", , "users" : [ { "userId":"vQIMLMo5CK9YqxpTZ", "admin" : 1 } ] }
The update do nothing and they are no error message
Thanks in advance for your help
EDIT 12/12/2015:
When I try to do update in client side, it's work good.
function joinTopic(topicId)
{
var user = Meteor.user();
Topics.update(topicId ,{ $addToSet: { users: { userId : user._id, admin: 0 }} });
}
But i have a problem when i want to use call function. In client side I have:
function joinTopic(topicId)
{
Meteor.call('joinTopic', { topicId: topicId });
}
and in server side, i have:
joinTopic: function (topicId)
{
Topics.update(topicId ,{ $addToSet: { users: { userId : this.userId, admin: 0 }}});
}

Answer 1

OK, I found my stupid mistake !
I had to do:
Meteor.call('joinTopic', topicId);
instead of:
Meteor.call('joinTopic', { topicId: topicId });