What's the fastest way to check for the existence of a mongodb doc?

What's the fastest way to check for the existence of a mongodb doc?

Should I just use find and if it returns nothing?

EDIT:

collection.findOne {#attribute}, (err, doc) ->

 开发者_运维问答   if err then console.log err

    if interaction
        #exists
    else
        #does not

If you are just testing for a single document, use findOne (or the equivalent in your driver); most drivers implement this in the most efficient possible way (by setting a negative limit of 1 on the request, which asks mongo to return immediately after finding one document, even if more might match, and not to create a cursor that won't ever be used by the client).

If you have an index that can serve your query, you can use field selection to select (a subset of) the fields in the index; this will make use of Mongo's "covered index" functionality to avoid a lookup to the underlying collection data. Be sure to set {_id: 0} in your field selector unless _id is in your index.

Covered Index is what you want. If the info you know about the document is indexed, then you can use this facility to query and retrieve info from the index only (in RAM) and will not go to disk to get the reference document. Explained in the mongo docs here.

http://www.mongodb.org/display/DOCS/mongo%20wire%20protocol#MongoWireProtocol-OPQUERY

numberToReturn : Limits the number of documents in the first CONTRIB:OP_REPLY message to the query. However, the database will still establish a cursor and return the cursorID to the client if there are more results than numberToReturn. If the client driver offers 'limit' functionality (like the SQL LIMIT keyword), then it is up to the client driver to ensure that no more than the specified number of document are returned to the calling application. If numberToReturn is 0, the db will used the default return size. If the number is negative, then the database will return that number and close the cursor. No futher results for that query can be fetched. If numberToReturn is 1 the server will treat it as -1 (closing the cursor automatically).