Domain Model vs Data Model – Example Differences in C#

asp.net-corecdata modelingdomain-driven-designdomain-model

I've seen many articles describing differences between Domain Model and Data Model. However none of the articles have picture representations showing difference.

https://stackoverflow.com/questions/3507671/whats-the-difference-between-data-modelling-and-domain-modelling

Can someone provide a picture example showing difference, maybe a simple example with customers or orders, anything?
I saw one example below from resource here, however the example difference seems very little (box in red) : https://study.com/academy/lesson/domain-model-vs-data-model.html

Can someone provide an example showing a larger difference between Domain and Data? This way readers can understand

Note: Seen article Why do 'some examples' and 'list of things' questions get closed?
, yet have not read concise example on the internet showing Large differences between domain and data model, anything would help.

Best Answer

I've seen many articles describing differences between Domain Model and Data Model. However none of the articles have picture representations showing difference.

Brian Lawler's article Domain First vs Schema First Architecture might help.

Or Scott Wambler Why Data Models Shouldn't Drive Object Models

Your best bet might be to look for domain models that use event sourcing. The distinction between the domain model and the data model may be more clear when the domain model looks like business entities and the data model looks like sequences of messages.

But my searches in that vein weren't able to turn up images that I thought would be helpful.

Related Solutions

Tools and Patterns for Business Rules in C#

I'd make a ValidationProvider class that'll get your validators on demand, given any domain state.

like:

public class UserValidatorProvider
{
    public static IValidator GetValidator(User user)
    {
        if(user.Age > 40){
            return validator1;//you'd probably use the fluent api here
        }else{
            return validator2;//or maybe encapsulate that fluent in a ctor of a class like new UserOver40Validator()
        }
    }
}

That is, a Domain has a State (like, the user is over 40), given a State select a Validator.

You'd have to swap validators at runtime.

As for where to put them in the layers, you will have different validation procedures for each use case at all layers necessary. That is, UI feedback, Business Rules, Domain Validation, but only where needed.

I think it's that simple!

C# – Using a GUID as a Primary Key

GUIDs are by definition "Globally Unique IDentifiers". There's a similar but slightly different concept in Java called UUIDs "Universally Unique IDentifiers". The names are interchangeable for all practical use.

GUIDs are central to how Microsoft envisioned database clustering to work, and if you need to incorporate data from sometimes connected sources, they really help prevent data collisions.

Some Pro-GUID Facts:

GUIDs prevent key collisions
GUIDs help with merging data between networks, machines, etc.
SQL Server has support for semi-sequential GUIDS to help minimize index fragmentation (ref, some caveats)

Some Ugliness with GUIDs

They are big, 16 bytes each
They are out of order, so you can't sort on ID and hope to get the insertion order like you can on auto-increment ids
They are more cumbersome to work with, particularly on small data sets (like look up tables)
The new GUID implementation is more robust on SQL Server than it is in the C# library (you can have sequential GUIDS from SQL Server, in C# it is random)

GUIDs will make your indexes bigger, so the disk space cost of indexing a column will be higher. Random GUIDs will fragment your indexes.

If you know you aren't going to synchronize data from different networks, GUIDs can carry more overhead than they are worth.

If you have a need to ingest data from sometimes connected clients, they can be a lot more robust for preventing key collisions than relying on setting sequence ranges for those clients.

Best Answer

Related Solutions

Tools and Patterns for Business Rules in C#

C# – Using a GUID as a Primary Key

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