When developing a Model for an MVP architecture it needs at some point to access the database to read and write data. When this model is running on the client-side (in Silverlight for example) it has no access to the database. I suppose the standard solution here is to put the data access code in a separate class running on the server. The client then invokes this service passing the data required.
The approach obviously works, but I don't like it. The Model contains all the data relevant to the business problem. It has the validation logic for the data. Why do I need to suddenly create an entirely different service just to read and write to the database? Now with LINQ there are no code-level ties to a particular database technology.
The Model should be in charge of telling the database what data it needs, reading the data and storing into its fields. When saving data the Model should tell the database what query to execute to save the data.
The root of the problem here is that the Model needs to be split between the client and server sides. However, I want this to be done in such a way that the developer is not wading through plumbing and service layers. In essence, I want this:
[DataContract]public class Model : IModel{ [DataMember] public string CustomerName { get; set; } [DataMember] public decimal InvoiceAmount { get; set; } [RunAtServer] public void Load(int id) { // Access database here. Get data. Save into properties. }}
This needs to generate two Model classes, one for the server (which is basically the same as above) and one for the client that replaces the [RunAtServer] methods with calls to a service object.
I have this working! :) I have used my C# macro tool to take the above code and generate a new file that contains the two Models, a WCF service and client proxy. These classes are surrounded by "#IF SERVER" and "#IF !SERVER". I then have a WCF service project and Client project that both compile the generated file. The conditional preprocessor directives mean each project only gets what it needs.
This is all still prototype-level code, but it does work. I am waiting on Silverlight 1.1 to have better support for WCF, so for now I'm using XBAPs to test. However, there is nothing stopping me using WinForms for the client as well. I see this as being a great way to write rich internet applications. I can focus on modelling the business problem and just decorate any methods that need to be remote with an attribute.
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