use variable as key name in mongo db with modifier - node.js

Question

I am trying to insert a bunch of arrays into mongoDB.
The data looks something like:
var places = {
city: ['london', 'york', 'liverpool'],
country: ['uk', 'france']
};
Each time I add an array, some of the entries could already be there, so I want to ensure there are no duplicates.
db.collection('places').ensureIndex({'city': 1}, {unique: true }, function(){ });
db.collection('places').ensureIndex({'country': 1}, {unique: true }, function(){ });
I then need to loop through the places object and add each item:
for(var key in places){
db.collection('places').update({_id: 1}, { $addToSet: { key: { $each places[key] } } }, function(err, docs){
if(err){
console.log(err);
}else{
console.log('success');
}
});
}
Here I need key to be the actual keys: 'city', 'country'. Rather than literally being 'key'. But I cant see how this can be achieved with with the modifiers in place.

Answer 1

You need to build up your $addToSet value programmatically:
for(var key in places){
var addToSet = {};
addToSet[key] = { $each: places[key] };
db.collection('places').update({_id: 1}, {$addToSet: addToSet}, function(err, docs){
if(err){
console.log(err);
}else{
console.log('success');
}
});
}
But you can do this more efficiently by combining both updates into one:
var addToSet = {};
for(var key in places){
addToSet[key] = { $each: places[key] };
}
db.collection('places').update({_id: 1}, {$addToSet: addToSet}, function(err, docs){
if(err){
console.log(err);
}else{
console.log('success');
}
});