Null int/float columns with TableAdapters

[Nick Gilbert]

Hi,

I have a database table which has some "float" columns which allow
nulls. I have created a TableAdapter to view this table.

If I open the TableAdapter and there are null values for some of the
float columns then an exception is thrown:

Line 2136: try {
Line 2137: return
((double)(this[this.tableProducts.MaxPressureBarColumn]));
Line 2138: }
Line 2139: catch (System.InvalidCastException e) {

[StrongTypingException: The value for column 'MaxPressureBar' in table
'Products' is DBNull.]

With string values, you can change the NullValue property to "null" in
the xsd file and all is well - however it won't let you do this for
anything other than strings even though .NET 2 supports null values for
ints floats and decimals etc...

Is there any way I can make this work? Or some kind of workaround I can use?

The only thing I can think to do is prevent the float columns from being
null and use 0 instead. But for some of the columns, zero is a valid
value and I need to be able to distinguish between 0 and null in the code.

Help!

Nick...

 

[Walter Wang [MSFT]]

Hi Nick,

This is a known issue of typed DataSet in .NET 2.0. The generated code
snippet is actually from the typed DataSet (for example:
DataSet1.Table3Row) rather than the TableAdapter. As the TableAdapter's
documentation (http://msdn2.microsoft.com/en-us/library/bz9tthwx.aspx)
claimed: The TableAdapters support nullable types Nullable(Of T) and T?.
You should see the Insert or Update method of your TableAdapter does use
"System.Nullable<double>" as parameter data type.

We looked really closely at extending typed DataSet to support Nullable
types. However, Nullable types were added a bit late in the cycle and we
just didn't have the time to work out all the plumbing issues up and down
the stack. Because typed DataSet serializes into untyped DataSets, and due
to the way DataBinding works with Views, adding Nullable types in the
strongly typed DataSet was problematic. Another issue is related to
compatibility with .NET 1.x.

There's already a related feedbak on this issue:

http://connect.microsoft.com/VisualStudio/feedback/ViewFeedback.aspx?Feedbac
kID=121229

As the product team responded, it will be considered for a future
enhancement. Thank you for your feedback!

Hope this helps. Please feel free to post here if anything is unclear.

Sincerely,
Walter Wang ([email protected], remove 'online.')
Microsoft Online Community Support

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