Use Null Object Pattern in Your Rich Domain Model
The source code from this demo is available on Patreon: / use-null-object-83554737
Ever wondered about the impact of the Null Object design pattern on domain modeling? This video offers a deep dive into this fascinating topic, demonstrating how identifying objects that behave like 'zero' can create a more intuitive and friendly model, even in a complex business domain.
We bring this concept to life through a real-world example, demonstrating the significant influence of 'null objects' in a deep domain model when it comes to implementing essential features. Watch this video to experience this simplifying effect firsthand!
And not just that, we also reveal situations where you might want to avoid using the Null Object pattern by adding a touch of complexity to your classes, but gaining more from their simple and intuitive public interface. Discover why maintaining a simple public interface could be advantageous over polymorphic Null Object implementation.
By the end of this journey, you'll be equipped with the know-how to apply these concepts creatively in your domain modeling, ultimately leading to more structured code.
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#dotnet #csharp #designpatterns
Excellent presentation. Well balanced. None of the "Your doing X wrong!!" hysterics here.
The greatest secret of software design is that every decision is a tradeof.
I rarely watch videos twice. This one opened my eyes. I think your videos are reminding us how we should look at the code.
Thank you for your comment. I am glad to hear the video was helpful.
Essentially creating an algebra by adding an Identity element under the Add binary operator.
Great presentation from one of my favorite instructors! Making my development team watch it.
Haven’t programmed in C# for a couple of years now, still loving the examples. Good job !
omg, a list of my favorite books.
Thank you again Zoran. Brilliant video!
Thank you for not using the default 'Order, product and Order Items' examples. 😊
Of course :)
Thank you for the impressive video, as always.
Another excellent video sir!
"poor man's polymorphism"
Oh yes, you can find it everywhere.
That makes you wonder which one is rich man polymorphism
@@josebarria3233 Just polymorphism.
@@josebarria3233 Probably a refinement type, so you can specify a nominal base type, but then a refined subtype is one that meets some condition like `amount == 0`. That way you could group the changes in the behavior of each subtype.
Ming the Merciless retired as a coder?
I'm loving your videos! Do you have plans to make content about async programming and synchronization?
I have one video in the queue that talks about asynchronous programming, which I might record in the near future.
@@zoran-horvat glad to hear it, thank you!
IMO there's a flaw in your current implementation, as it is possible create a Money object with Currency.Empty and a non-zero amount. So it is possible to handle money without a currency. A possible solution is to throw an exception in the constructor if currency equals Currency.Empty. Also I would rename Currency.Empty to Currency.None, as there's no such thing as an "empty" currency.
Good observations.
Great ideas and insights. Not a big fan of throwing exceptions in this case, thought.
There is a more complex design where Money separates "strict" addition from that with mixed currencies. However, subtraction can never be with mixed currencies, except for subtracting a zero... For a 100% safe and sound solution, we would need to return an Either monad from all strict methods. But with no syntactic support for errors in C#, the implementation and its use would become significantly more complex and less readable.
This is really interesting because calling it the "null" pattern shows how null conflates two related ideas; that of zero and bottom. There are really two patterns: the zero object pattern and the bottom type pattern. And, in most languages, you use a "bottom object" to work around the lack of support for a proper bottom type. The number 0 is a regular number, it's only special in how arithmetic works. It is a zero object in itself, since it checks all the boxes of a regular number. A bottom type, though, is the type with no values, sometimes called void or nothing. (As many people find it hard to accept that 1/0 doesn't have a value, we also intuitively want to have a bottom value, which I think is where null and undefined come from.) Here, Currency.Empty is properly the _absence_ of a currency. But C# doesn't really let you indicate the absence of a value, so you're (reasonably) using the bottom object pattern. Notably, it doesn't check all the boxes of a currency; especially, you can only have 0 of it. And the relation between zero and bottom is that you use Currency.Empty to create Money(0, Currency.Empty); the bottom type is often an element of a zero value. Another example: if you have immutable (and thus covariant) lists, the element type for the empty list would be Bottom. Since Bottom is a subtype of all types, List concat List gives you a List, as X is the common supertype of X and Bottom. And, a List is always the empty list (the zero value for List) since you can never get a value of type Bottom.
Very nice explanation, thank you.