in ASP net 2.0
a function that query/add item to cache:
public function1
.... ... ..
If HttpContext.Current.Cache(myKey) Is Nothing Then
Dim ds As DataSet = functionToCreateDataset.... ...
HttpContext.Current.Cache.Insert(myKey, ds, Nothing)
End If
Return HttpContext.Current.Cache

in the web form code behind, I have:
Dim ds As DataSet = Cache("myKey")
dim ds as dataset
ds.Tables(0).Columns.Add("customCol", GetType(String), "col1+'- '+col2")


the problem is, when "function1" create the cache the first time, the
statement:
ds.Tables(0).Columns.Add("col1", GetType(String), "col1+'- '+col2")
works fine. But when "function1" returned the cached item, the same
statement display the error:
"A column named 'customCol' already belongs to this DataTable."

it looks like the cache get changed too when the dataset derived from it is
changed.
how can I fix that ?

This is an error, you have ds declared twice, it's most likely a typo. I
wouldn't expect that to compile:

Dim ds As DataSet = Cache("myKey")
dim ds as dataset

When you first create your dataset, it contains a column named customCol.
You can, at any point later, add another column with that name because
column names are explicitly unique.

--
Regards,
Alvin Bruney
------------------------------------------------------
Shameless author plug
Excel Services for .NET is coming...
OWC Black book on Amazon and
www.lulu.com/owc
Professional VSTO 2005 - Wrox/Wiley


"zino" <zino (AT) noemail (DOT) noemail> wrote

there is a little confusion here.
the issue is :
- a datatable consisting of 2 column is created and added to the cache.
(cache("myDt") )

- a variable derived from a call to this cache :
Dim dt2 As DataTable = CType(Cache("myDt"), DataTable)

the following: dt2.Columns.Count will return: 2


now,
any change to dt2 as:
dt2.Columns.Add("customCol", GetType(String), "col1+'- '+col2") , is
changing cache("myDt") too.

after the previous statement:
the following:
Dim dt3 As DataTable = CType(Cache("myDt"), DataTable)
dt3.Columns.Count will return: 3


why 3 ??
Why the change done on dt2 propagated back to the cache ?

Sorry if I am out of left field because the original thread isn't included.
Cache holds live object references not copies. Well, the copy is a pointer
reference that *points to the live object.

--
Regards,
Alvin Bruney
------------------------------------------------------
Shameless author plug
Excel Services for .NET is coming...
OWC Black book on Amazon and
www.lulu.com/owc
Professional VSTO 2005 - Wrox/Wiley


"zino" <zino (AT) noemail (DOT) noemail> wrote

Thank you.
that answers my question.

"Alvin Bruney [MVP]" wrote: