This second post in “Fun With NoRM” will be about querying…

How to get everything

Querying collections can be done easily with the anonymous types of C# 3 – e.g. the Order collection from my previous post can be queried for all orders like so:

var orders = mongo.GetCollection<Order>();
 
var allOrders = orders.Find();

How to use criteria

If we’re looking for some particular order, we can query by field values like so:

var orderNumber2 = orders.Find(new { Number = 2 });

or by using the query operators residing in the static class Q:

var ordersWithNumberGreaterThan2 = orders.Find(new { Number = Q.GreaterThan(2) });

More advanced criteria

The query operators can even be combined by combining criteria like so:

var ordersWithNumberBetween5And10 = orders.Find(new { Number = Q.GreaterThan(5).And.LessThan(10) });

Now, what about the nifty dot notation? This an example where C#’s capabilities don’t cut it anymore, as everything on the left side in an anonymous type need to be valid identifiers – so no dots in property names!

This is solved in NoRM by introducing Expando! (not to be confused with ExpandoObject of .NET 4, even though they have similarities…)

Expando is just a dictionary, so to query by the field of an embedded object, do it like so:

var q = new Expando();
q["Items.Name"] = "beer";
var ordersWithBeer = orders.Find(q);

As you can see, querying with NoRM is pretty easy – and I think the NoRM guys have found a pretty decent workaround in the case of dot notation, where C#’s syntax could not be bent further.

Stay tuned for more posts…