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…