Dynamic Documents

More things coming out from my recent session about MongoDB.

Documents and Types

MongoDB is a document database. Such documents are stored as JSON (well, kind of). JSON has a very challenged simple type system.
.NET is an object-oriented environment that promotes types. Such type system is pretty rich.

Are MongoDB’s documents and .NET Framework types doomed to miscommunicate? They would be if not for the existence of the serialization bridge the driver provides.

Types Everywhere

Since .NET is type-happy, majority of the times we are working in our happy strongly-typed world.
Believe it or not, there developers out there that are very happy (and productive) in a less strongly-typed world.

I will measure my words carefully, trying to prevent them understood as heresy:

There are certain types of applications (or parts of all applications) where strong typing bring little benefits.

Wow. There I said it.

Imagine this scenario: data is carefully crafted and validated and taken care of at the time of writing it to persistence storage and whenever needs to be presented to the user, there is little (if any) manipulation of it, because those details were taken care of beforehand, at a time when computing cost is not so important as write operations tend to be fewer than read operations. For what is worth, we could be storing textual representations of the data and no one would care if that was the case.

In those scenarios we do not need types. The structured data only travels through the wire to be presented on a screen.

Type-wannabe: the Document

The serialization part of the MongoDB driver for C# offers a straightforward type to solve the problem: BsonDocument. It is a nicely designed and useful type that allows reading information from MongoDB without much fuss about the underlying type.

The “downside”? C# is not helping to have a clean syntax.

Let’s take this simple document:

And how to access “when I started snowboarding?“:

From 33 to 42 characters. It does not look like much, but it’s a whooping 27% increase in typing.
I do not know about you, but I would gladly accept a 27% increase in my paycheck, thank you very much.

Lipstick on a Type

In .NET 4, dynamics were introduced as a way to marry two different worlds: strongly and loosely typed with a more palatable syntax. I suspect it was just a trick to prevent developers doing Interop from quitting in mass.

That sounds like almost useful and applicable to our small problem in hand.

Unfortunately, the driver still lives in a pre-.NET 4 era, so they cannot provide out-of-the-box support for dynamics. There are some attempts out there, but I was not happy with taking a dependency on another (arguably more capable) JSON parsing library (JSON.Net) to just do that.

Since it was for educational purposes you are allowed to simply waste some of your scarce free time in search for a solution that no one cares about Smile

Dynamic document

It turns out it is really easy to provide support for accessing instances of BsonDocument as dynamic object, taking benefit from the usual dot notation. Thanks to DynamicObject.

By simply wrapping an instance of BsonDocument inside an inheritor of DynamicObject and overriding .TryGetMember() to wrap nested documents we are able to happily use dot notation (with a slight overhead):

To use it, just invoke the .AsDynamic() over an instance of BsonDocument

With this minimal baggage, you are able to, for example, write razor views that display data coming from an instance of such DynamicBsonDocument.

As for getting dynamic objects into BsonDocument instances… Well, that is a whole different story. That I am not ready or willing to tell… for the moment Winking smile

Kategorier: Udvikling

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