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    <p>I was typing the same as Daimon's first answer, using <code>sort</code> and <code>limit</code>. This is probably not recommended, especially with some drivers (which use random numbers instead of increments for the least significant portion), because of the way the _id is generated. It has second [as opposed to something smaller, like millisecond] resolution as the most significant portion, but the last number can be a random number. So if you had a user save twice in a second (probably not likely, but worth noting), you might end up with a slightly out of order latest document.</p> <p>See <a href="http://www.mongodb.org/display/DOCS/Object+IDs#ObjectIDs-BSONObjectIDSpecification" rel="nofollow">http://www.mongodb.org/display/DOCS/Object+IDs#ObjectIDs-BSONObjectIDSpecification</a> for more details on the structure of the ObjectID.</p> <p>I would recommend adding an explicit versionNumber field to your documents, so you can query in a similar fashion using that field, like so:</p> <pre><code>db.coll.find({documentId: &lt;id&gt;}).sort({versionNum: -1}).limit(1); </code></pre> <p><strong>edit to answer question in comments</strong></p> <p>You can store a regular DateTime directly in MongoDB, but it will only store the milliseconds precision in a "DateTime" format in MongoDB. If that's good enough, it's simpler to do.</p> <pre><code>BsonDocument doc = new BsonDocument("dt", DateTime.UtcNow); coll.Insert (doc); doc = coll.FindOne(); // see it doesn't have precision... Console.WriteLine(doc.GetValue("dt").AsUniversalTime.Ticks); </code></pre> <p>If you want .NET DateTime (ticks)/Timestamp precision, you can do a bunch of casts to get it to work, like:</p> <pre><code>BsonDocument doc = new BsonDocument("dt", new BsonTimestamp(DateTime.UtcNow.Ticks)); coll.Insert (doc); doc = coll.FindOne(); // see it does have precision Console.WriteLine(new DateTime(doc.GetValue("dt").AsBsonTimestamp.Value).Ticks); </code></pre> <p><strong>update again!</strong></p> <p>Looks like the real use for BsonTimestamp is to generate unique timestamps within a second resolution. So, you're not really supposed to abuse them as I have in the last few lines of code, and it actually will probably screw up the ordering of results. If you need to store the DateTime at a Tick (100 nanosecond) resolution, you probably should just store the 64-bit int "ticks", which will be sortable in mongodb, and then wrap it in a DateTime after you pull it out of the database again, like so:</p> <pre><code>BsonDocument doc = new BsonDocument("dt", DateTime.UtcNow.Ticks); coll.Insert (doc); doc = coll.FindOne(); DateTime dt = new DateTime(doc.GetValue("dt").AsInt64); // see it does have precision Console.WriteLine(dt.Ticks); </code></pre>
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    1. POMongoDB - most efficient way of getting the last version of a document
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    1. USEve Freeman
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    1. COThanks wes, you mean like an integer number for the version?
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    2. COUsing integer counters is possible but it's not scalable at all... use of high resolution timestamp would be better approach - there is always a chance that two documents would share same timestamp - but if it's mission-critical in your case maybe using RDBMS is better approach?
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    3. COOk. Makes sense. It's not mission critical, but obviously needs to work. Difficult leaving RDBMS concepts behind. Thanks for your input (both)
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