Question

I have a two part application. One part is a web application (C# 4.0) which runs on a hosted machine with a hosted MSSQL database. That’s nice and standard. The other part is a Windows Application that runs locally on our network and accesses both our main database (Advantage) and the web database. The website has no way to access the Advantage database.

Currently this setup works just fine (provided the network is working), but we’re now in the process of rebuilding the website and upgrading it from a Web Forms /.NET 2.0 / VB site to a MVC3 / .NET 4.0 / C# site. As part of the rebuild, we’re adding a number of new tables where the internal database has all the data, and the web database has a subset thereof.

In the internal application, tables in the database are represented by classes which use reflection and attribute flags to populate themselves. For example:

[AdvantageTable("warranty")]
public class Warranty : AdvantageTable
{
    [Advantage("id", IsKey = true)]
    public int programID;
    [Advantage("w_cost")]
    public decimal cost;
    [Advantage("w_price")]
    public decimal price;

    public Warranty(int id)
    {
        this.programID = id;
        Initialize();
    }
}

The AdvantageTable class’s Initialize() method uses reflection to build a query based on all the keys and their values, and then populates each field based on the database column specified. Updates work similarly – We call AdvantageTable.Update() on whichever object, and it handles all the database writes. It works quite well, hides all the standard CRUD, and lets us rapidly create new classes when we add a new table. We’d rather not change it, but I’m not going to entirely rule it out if there’s a solution that would require it.

The web database needs to have this table, but doesn’t have a need for the cost data. I could create a separate class that’s backed by the web database (via stored procedures, reflection, LINQ-TO-SQL, ADO data objects, etc), but there may be other functionality in the Warranty object which I want to behave the same way regardless of whether it’s called from the website or the internal app, without the need to maintain two sets of code. For example, we might change the logic of how we decide which warranty applies to a product – I want to need to create and test that in only one place, not two.

So my question is: Can anyone think of a good way to allow this class to sometimes be populated from the Advantage database and sometimes the web database? It’s not just a matter of connection strings, because they have two very different methods of access (even aside from the reflection). I considered adding [Web("id")] type tags to the Advantage tags, and only putting them on the fields which exist in the web database to designate its columns, then having a switch of some kind to control which set of logic is used for reading/writing, but I have the feeling that that would get painful (Is this method web-safe? How do I set the flag before instantiating it?). So I have no ideas I like and suspect there’s a solution I’m not even aware exists. Any input?

Answer 1

The solution I eventually came up with was two-fold. First, I used Linq-to-sql to generate objects for each web table. Then, I derived a new class from AdvantageTable called AdvantageWebTable<TABLEOBJECT>, which contains the web specific code, and added web specific attributes. So now the class looks like this:

[AdvantageTable(“warranty”)]

public class Warranty : AdvantageWebTable<WebObjs.Warranty>
{
    [Advantage("id", IsKey = true)][Web("ID", IsKey = true)]
    public int programID;
    [Advantage("w_cost")][Web("Cost")]
    public decimal cost;
    [Advantage("w_price")][Web("Price")]
    public decimal price;

    public Warranty(int id)
    {
        this.programID = id;
        Initialize();
    }
}

There’s also hooks for populating web-only fields right before saving to the web database, and there will be (but isn’t yet since I haven’t needed it) a LoadFromWeb() function which uses reflection to populate the fields.