 <p>This can be done with the collection method "find" as you did, but the selector must be a hash.</p> <pre><code> col = db.collection(main) record = col.find({:property =&gt; value}) </code></pre> <p>Find also accepts an optional hash of options. Take a look at the documentation. <a href="http://api.mongodb.org/ruby/current/Mongo/Collection.html#find-instance_method" rel="nofollow">http://api.mongodb.org/ruby/current/Mongo/Collection.html#find-instance_method</a></p>