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I need some clarification about a stange DataView behaviour I have noticed. I am developing a dynamic website that is binding data (from an Access db) to a datagrid. I use a cached dataset to save trips to the db, here is the code...
'populate the Cache Variable that stores the Web Content Dataset
Public Function PopulateWebContentDataset(Optional ByVal blnRepopulate As Boolean = False) As Boolean Dim ds As New DataSet()
'check if cached dataset already exists
If Current.Cache("WebContent") Is Nothing = False Then
'the cached variable already exists
Return True
End If
'get the Web Content from the database
Dim cn As New OleDbConnection(AppSettings("cnStringWebContent"))
Dim da As New OleDbDataAdapter("SELECT * FROM tblWebContent", cn)
Try
'fill the Web Content dataset with records from the database
da.Fill(ds, "tblWebContent")
If ds.Tables("tblWebContent").Rows.Count > 0 Then
'add the dataset to the cache
Current.Cache.Insert("WebContent", ds, _
New System.Web.Caching.CacheDependency(AppSettings("dbPathWebContent")), _
DateTime.Now.AddDays(1), Current.Cache.NoSlidingExpiration, _
System.Web.Caching.CacheItemPriority.Normal, Nothing)
Return True
Else
'no records were found
Current.Cache.Remove("WebContent")
Current.Cache("WebContent") = Nothing
Return False
End If
Catch DefaultExc As Exception
Finally
cn.Dispose()
da.Dispose()
ds.Dispose()
End Try
End Function
Public Function BindPageContent(ByRef dgr As DataGrid, ByVal strPage As String, _
Optional ByVal blnRepopulate As Boolean = False) As Boolean
'check if the cache Web Content dataset already exists
If PopulateWebContentDataset(blnRepopulate) = False And blnRepopulate = False Then
'unable to get the information from the database
Return False
End If
Dim ds As DataSet
Dim dv As New DataView()
Try
ds = Current.Cache("WebContent")
'ds.Tables("tblWebContent").DefaultView.RowFilter = "Page=" & "'" & strPage & "'"
dv = ds.Tables("tblWebContent").DefaultView
dv.RowFilter = "Page=" & "'" & strPage & "'"
dgr.DataSource = dv
dgr.DataBind()
Catch DefaultExc As Exception
Finally
ds.Dispose()
dv.Dispose()
End Try
End Function
My question is, the above code works perfectly the first time the page loads but when I return to this specific page (which should be getting the cached dataset), nothing is displayed. I checked the dataset and it has the correct amount of rows, however, the dataview has a rowcount of 0 (when it previously had a rowcount of 1).
I have done the following to fix this problem, all of which have worked...
1. Instead of getting the dataset from the cache, I connected to the db on each page_load and repopulated the dataset
2. When I bind the datagrid using the dataset as the datasource instead of the dataview, it works...
(ds.tables("tblWebContent").defaultview.rowfilter="Page='" & strPage & "'")I have many instances in my code where I use the exact same code as posted above and it doesn't seem like there is a problem with the DataView. Should I re-examine all my code and remove dataview.dispose()? Does anyone have any suggestions on why this may be happening?
Do you need to call disposal methods in VB.net or is it just a formality to let the garbage collector know what it can kill?
In C# using a disposal method does not gaurantee a time when the garbage collection will happen. It just lets the collector know it is available. Could your problem be that it is collecting the memory too quickly?
