Question

I have these two related tables Client (ClientId, Name) and ClientDescription (ClientDescriptionId, (FK) ClientId, Description). That is to say each Client can have many associated descriptions. Now, when displaying the a list of ClientDescriptions, I also need to know what the Name of it’s associated Client is.

Now you’ll probably say that I allready have this information, since I can simply follow my navigation property back to the associated Client and use its Name. I can’t do that because I’m autogenerating a grid in Ria services, and this just gives me a count for navigation properties, and I haven’t found a way to flatten this down in my metadata file. Hence why I want a property.

The whole idea is that I want to be able to add a new field to my database, update my entity classes from the database and regenerate my domain service, and the new field should just pop up in my grid. I shouldn’t have to update my xaml just because my database happen to have an extra field.

So, what I would like to do is add a ClientName field to the entity (clr object), but keep my database clean (no such denormalization in the db).

So, I generated my edmx, and added a new property named ClientName. Set it to StoreGeneratedPattern.Computed, and compiled. I then get a nasty little error

Error 3004: Problem in mapping fragments starting at line NN: No mapping specified for properties (etc..)

The solution apparently is to generate my database from my edmx. (Or that’s what answers to questions about that error seems to yield.) But this generates an actual DB-field, which I don’t want, so that answer doesn’t apply to my case.

So my question is: How can I denormalize my clr entity, but keep my db tables normalized?

Edit: I guess this question can be generalized a bit. The issue would be the same if ClientDescription contained a few numeric fields that I wanted to do some calculations on, and I wanted the result available as a field and the algorithm should be in c# rather than in my database.

Answer 1

To answer your more generalized question:

Entities are generated by the Entity Framework with a partial keyword.
This means that the code of an entity can be split in multiple source files in the same namespace and assembly. One will contain the generated code from the Entity Framework, the other will contain custom properties and methods.

If for example, your entity has the database fields Price and Amount you could add a property in the partial class TotalPrice which would return Price * Amount.

Then the algorithm will be C# and your database won’t know about the extra property.