Detecting DataRow changes from within a partial class

Question

Let's say I have an interface representing a domain object:

public interface IFoo
{
    Bar Bar { get; }
}

The Bar type is a family of objects, each of which has a slightly different schema. In the database, this is represented as XML (this is a mobile app, so it is simply nvarchar, not a true XML column).

I have a generated DataSet which contains an FooDataTable and corresponding FooRow objects:

// AcmeDataSet.designer.cs

public partial class FooRow : DataRow
{
    public string BarXml
    {
        // Generated get and set
    }
}

I would like to implement IFoo and cache the deserialized instance of Bar:

// FooRow.cs

public partial class FooRow : IFoo
{
    private Bar _bar;

    Bar IFoo.Bar
    {
        get { return _bar; }
    }
}

How can I, from within the partial class, determine that the value of BarXml has changed?

I realize that FooDataTable contains ColumnChanging and ColumnChanged events, but I don't know how to subscribe to them. There is no analog to Linq to Sql's OnCreated partial method and I don't know of another way to hook into the generated constructor.

Answer 1

If I understand you correctly, then your FooRow object (the instance) is an instance of some type that derives from Type DataRow... If so, then since DataRow has a property that references the DataTable, just cast your IFoo variable to a DataRow,

Inside of FooRow

  public partial class FooRow
  {    
       private void myColumnChanging Handler(object sender, EventArgs e)
       {
            // Implementation
       }
       private void myColumnChanged Handler(object sender, EventArgs e)
       {
            // Implementation
       }
       public void RegisterEvents()
       {
          ((DataRow)this).Table.ColumnChanging += myColumnChanging; 
          ((DataRow)this).Table.ColumnChanged += myColumnChanged; 
       }
   }

Then, in FooDataTable class, add a new factory method, MyNewFooRow()

public class FooDataTable 
{
    //  -- Other implementation
    public FooRow MyNewFooRow()
    {
        FooRow fr = this.NewFooRow(); // call the original factory
        fr.RegisterEvents();
        return fr;
    }
 }

and use this new factory wherever you were using the old one...