Problems saving a dataset with a Calculated expression.

[R Neu via .NET 247]

I'm having the same issue, but with a hierarchical dataset in a many-to-many relationship.
TASK|--< TASKSTEP >--|STEP

My data adapter is correct as currently, Im removing the Expression from the calculated fields using the code below and can save/update the database.

<CODE>
//Clear the calculated columns
foreach(System.Data.DataTable dt in hierarchicalDataSet.Tables)
foreach (System.Data.DataColumn dc in dt.Columns)
{
if(dc.Expression.Length > 0)
{
if(dc.ExtendedProperties.ContainsKey("CalcExpression"))
dc.ExtendedProperties["CalcExpression"] = dc.Expression;
else
dc.ExtendedProperties.Add("CalcExpression",dc.Expression);
dc.Expression = "";
}
}
</CODE>

The problem is after the update. I attempt to place the Expressions back and get an error of
"Object not set to an instance of an object." on execution of :
dc.Expression = strTestVar; in the code below.

<CODE>
foreach(System.Data.DataTable dt in hierarchicalDataSet.Tables)
foreach (System.Data.DataColumn dc in dt.Columns)
{
if(dc.ExtendedProperties.ContainsKey("CalcExpression"))
{
try
{
strTestVar = dc.ExtendedProperties["CalcExpression"].ToString();
dc.Expression = strTestVar;
dc.ExtendedProperties.Remove("CalcExpression");
}
catch(Exception ex)
{
string str1 = ex.Message;
}
}
}
</CODE>

At first I thought the Expression was invalid, but if I add the following it will add the duplicate column with the Expression.

dt.Columns.Add(dc.ColumnName + "Duplicate" , dc.DataType, strTestVar);

Any thoughts??

 

[christian kuendig]

I suggest not using expressions at all



my experience is:

-it's kinda buggy

-I've not really understood the sense for placing the derivation logic
of derived attributes with a proprietary syntax into a schema (just because
a layer of abstraction is missing between the datasets and the ui widgets
;-))



using many-to-many relationships in a dataset doesn't work when you're in a
3-Tier scenario and using identity columns (lost of original client side row
identity)



I had some success when I accepted changes before resetting expression
strings



regards



Chris