mongo update query to ignore few fields in update operation - node.js

Question

I am using Nodejs based mongoskin driver for mongo database operation. I want to update my document however don't want to update few fields. Following are more details.
Request for add:
{
"name": "Theme Name",
"description": "Theme Description",
"createdByUserId": "53651221b25521601a5c9530",
}
Request for update:
{
"_id":"53555ef203dabf282b750a81"
"name": "Theme Name",
"categoryId": "53555ef203dabf282b750a81",
"description": "Theme Description",
"createdByUserId": "53651221b25521601a5c9530",
"updatedByUserId": "5675561b25521601a5c9530",
"dateCreated": ISODate("2014-05-19T19:47:26.603Z"),
"dateUpdated": ISODate("2014-05-19T19:49:28.203Z"),
}
I want to ignore following field send by client.
1. createdByUserId
2. dateCreated
For time being I am taking following approach in update operation:
1. Read collection for given _id
2. Read these above two fields from database and update the request and then perform database update operation
Looking help for clean approach.

Answer 1

Your request for update actually does the following: it replaces everything in the document with the values provided by the request (except for the "_id" of course, which is immutable). What you want is what is called a "partial update" in mongosphere. Please have a look into the $set operator. So what you would do is something like:
db.yourcollection.update({"_id":"53555ef203dabf282b750a81"},
{$set:
{
"categoryId":"53555ef203dabf282b750a81",
"updatedByUserId":"5675561b25521601a5c9530",
"dateUpdated":ISODate("2014-05-19T19:49:28.203Z")
}
}
)
As far as I know there is now way of sending a complete document to a mongo[s|d] and tell it to only skip certain fields.