Why does dataset designer prevent expressions for New MyDataset.MyTable?

microsoft.public.dotnet.framework.adonet

3 Feb 2007 2:49 AM

Richard Coltrane

Hi there,

I have created a dataset with two tables in it.One of those tables has an
expression that calcs a percentage based on two other columns. However when
i ran my app the UI was displaying (null) for the expression column. After
digging into the code I realised the designer automatically prevents
expressions from being loaded for a particular table if you declare an
instance of the table rather than an instance of the dataset as below:

<System.Diagnostics.DebuggerNonUserCodeAttribute()> _
Public Sub New()
Me.New(false)
End Sub

<System.Diagnostics.DebuggerNonUserCodeAttribute()> _
Friend Sub New(ByVal initExpressions As Boolean)
MyBase.New
Me.TableName = "KPI"
Me.BeginInit
Me.InitClass
If (initExpressions = true) Then
Me.InitExpressions
End If
Me.EndInit
End Sub

So if i

dim ds as new MyDataset

then table column expressions are good to go but if i

dim tbl as New MyDataset.MyDatatable

then as per the designer generated constructor above; expressions will be
disabled by default...... My question is why?? Why provide the ability to
declaratively set expressions on table columns if Im just going to have to
go ahead and reset them at runtime anyway? And more more importantly because
Im now going to overrride this default behaviour what problems can i expect
to encounter?
Considering this is Microsoft we're talking about I can only assume there is
a very good reason for the default behaviour.... as they only do anything
for very good reasons....... right?

Thanks alot

Richard