Saving unique array elements MongoDB - node.js

Question

I am trying to save a unique array of String elements using MongoDB but for some reason it allows me to save duplicates.
I am using mongoose. My code:
schema = mongoose.Schema({
"searchingId": { "type": String,
"unique": true,
"index": true },
"sharedTo" : {
type: [String],
unique: true,
"trim":true
}
}, {collection: 'myCollection'});
Basically the point is to keep a list of email addresses where the user had sent emails and to prevent the user from spamming them. But this schema will allow me to push any string to a sharedTo array and to .save() it no matter whether the duplicates exist. How to prevent this from happening?
EDIT:
Lahar's answer does help with my question but not entierly. I would like to prevent user from adding emails if there is at least one duplicate. So basically $addToSet will help with uniqueness but not with my question.

Answer 1

You can use $addToSet instead of $push to add email in "sharedTo" array.
That won't add duplicate element(email in your case).
By providing unique:true to whole array field won't check uniqueness of array element.
Please check $addToSet documentation.

Answer 2

you can implement your own static function that will run from the schema class to do this for every email entered
UserSchema.statics.findUseremail = function(useremail, suffix,
callback) {
var _this = this;
var possibleuseremail = useremail + (suffix || '');
_this.findOne({
useremail: possibleuseremail
}, function(err, userem) {
if (!err) {
if (!userem) {
callback(findUseremail);
} else {
return _this.findUseremail(useremail, (suffix || 0) +
1, callback);
}
} else {
callback(null);
}
});
};

Answer 3

So looks like I had found the solution myself but thanks to the Lahar Shah answer for pointing me in the right direction. Instead of using
Model.update(conditions, doc, [options], [callback])
I did
fetching the object
Added each of emails to my sharedTo attribute while checking for duplicates.
saving the object if no duplicates
Code:
var length = emails.length;
for( var i = 0; i < length; i++ ) {
var saved = doc.sharedTo.addToSet(emails[i]).length;
if (saved != 1) {
//status 409 - You have already sent email to user emails[i]
return;
}
}
doc[0].save(function(fail, success) {
if(fail) {
//error
} else {
//success return 200
}
});