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Querying a dataset

Posted on 2006-05-14
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Last Modified: 2010-04-23
Hi Guys

I am using a dataset to hold a whole lot of entries for a competition then I use a randon number to select which row won what I then want to do is update the dataset by removing all instances of the winners phone number as I need to choose more than one winner and don't want to return the same user more than once. I could loop thorugh all the rows deleting it if it has that number but that seems very time consuming. Is there a way to remove rows with a query?

Also I am populating the dataset using a SqlDataAdapter if I do remove rows from the dataset that will not delete anything from the original tables in the database correct?

Thanks
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Question by:peter58
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Expert Comment

by:ZeonFlash
ID: 16678650
Assuming that you have your original dataset (dsEntries) with a column called "PhoneNumber", you can create a DataView to filter the winning phone numbers.  Your row filter can be a string that you continually build upon, so for your first winner, your string might look like:  
     strFilter = "PhoneNumber <> " & strWinnerPhone

and to filter out your second winner (along with the first), it would like like:  
     strFilter &= " and PhoneNumber <> " & strWinnerPhone2

It seems to be more efficient to filter out a couple rows, instead of removing them all together, unless your going to be filtering out more than 50% of your entrants.

As an example --

     Dim strWinnerPhone As String = "5551234"
     Dim strWinnerPhone2 As String = "5555678"
     Dim dvNonWinners As New DataView(dsEntries.Tables(0))

     dvNonWinners.RowFilter = "PhoneNumber <> " & strWinnerPhone & " and PhoneNumber <> " & strWinnerPhone2
     DataGrid2.DataSource = dvNonWinners

To answer your second question, the DataAdapter will not cause any rows to be removed from the actual database until you fire the .Update method on the DataAdapter (assuming it has a Delete Command present).
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by:peter58
ID: 16678735
I am not displaying the results, I need the resulting data to be in something where I can reference a row by number, ie ds.Tables("Golf").Rows(1).Item("PhoneNumber") That way I can use a random number to get the row I want. Can I use a datagrid to select a row by number or can I put the results of the DataView in a temp dataset.
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Accepted Solution

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anyoneis earned 1000 total points
ID: 16679103
Why not add a column to the table, say "Eligible", that defaults to true. When you load the table, every row will get the default value. When they are chosen, you set "Eligible" to false.

' After you have loaded the data, asdd the column
Dim dc as DataColumn = new DataColumn("Eligible", System.Type.GetType("System.Boolean"))
dc.DefaultValue = true;
ds.Tables("Golf").Columns.Add(dc)


You want to work with a filtered view, so code something like:

dim filteredView as DataView = ds.CreateDataView(ds.Tables("Golf"))
filteredView.RowFilter = "Eligible = true"

Now, always go against the filteredView. When you generate the random number, make the high value one less than filteredView.Count. Rows that have Eligible set to false are not in the view, even though they are still in the table.

David
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LVL 4

Author Comment

by:peter58
ID: 16679217
Sounds good, but can I select a row using it's index in a view? eg Row(5)?
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LVL 4

Author Comment

by:peter58
ID: 16679227
One more thing is it possible to update the eligible field in the dataset using a query eg "update me set eligible = 0 where phonenumber = '5551234'"
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LVL 11

Expert Comment

by:anyoneis
ID: 16687325
A quick trip to the DataView docs will tell you all about accessing a row in a view. Yes, you can use an index.

In my example, you would set the eligible column value for a record with something like:

filteredView(index)("Eligible") = false

David
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