How to get " TOP(X)" rows from a DataView?

[jensen bredal]

I have a dataView and i only want to get the first x rows .

Is there a way of doing this without using Foreach?

Thanks

JB

 

[Bob Powell [MVP]]

Am I missing something obvious by suggesting that you use an SQL statement
that only gets the rows you need?

Such as "SELECT TOP 10 * FROM musictracks WHERE genre = "Jazz" ORDER BY
artist;"

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Visual C#, System.Drawing

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[jensen bredal]

Well, i have cached my dataview and i want to any time extract x rows from
it.
X may varie from time to time depending on the user of the apllication.
The problem , is that i want to have it cached so a select wouldn't do,
Or would be prefered on the cached dataview.

Hope that was a bit more clear.
JB

 

[jensen bredal]

By reading the documentatation , it does not look like on can use:

"SELECT TOP 10 * FROM musictracks WHERE genre = "Jazz" ORDER BY

on the RowFilter property.

 

[W.G. Ryan eMVP]

Add a DataColumn to you datatable and set the AutoIncrment value to true.
This will create a sequence for you. Make sure the data is sorted
beforehand in the order that you want. THen you can just use Rowfilter =
"ComputedColumn < 50"

 

[Ignacio Machin \( .NET/ C# MVP \)]

Hi,

AFAIK this feature does not exist in the framework, ITOH it's easily
doable, just wrap ( or extend ) DataView , add a botton/top limit and recode
the indexer

The wrap is the easiest thing to do as you probably only need this filtering

Cheers,

 

[jensen bredal]

The wrap is the easiest thing to do as you probably only need this

filtering

Cheers,

Well i would appreciate sample code for your solution as it will extend my
horizons a bit furthere although i find Ryans solution very appropriate for
my need.

Many Thanks
JB

 

[W.G. Ryan eMVP]

Jensen:

Here's a quick mockup of how it'll work:

private void SimulateTop(System.Int32 topValue){

DataTable SampleTable = new DataTable("JensensTable");

//DataAdapter fill code in here.

DataColumn ExpressionColumn = new DataColumn("Indexer",
typeof(System.Int32));

ExpressionColumn.AutoIncrement = true;

ExpressionColumn.AutoIncrementStep = 1;//It defaults to 1 - I just put it
here for clarity

ExpressionColumn.AutoIncrementSeed = 0;//Again, it defaults to this - I just
included it for clarity

DataView SampleView = SampleTable.DefaultView;

SampleView.RowFilter = "Indexer < " + topValue.ToString();

//You may want to include a minValue as well and change the rowfilter so
that you can specify other

//ranges, but by defaulting to 0 - you'll effectively have your Top
Condition

}

 

[jensen bredal]

Great ,Great i did in fact got right. The only things i did not include in
my code was
ExpressionColumn.AutoIncrementStep = 1
and

ExpressionColumn.AutoIncrementSeed =0;

But as you mentioned, if they default to theses values then i guess i'm
happy.

I think i perfectly understood your explaination the first time. But it is
also nice to know that
your code is in fact is what i did.


Again thank you so much


JB

 

[jensen bredal]

Hi Ryan,
there is some problem with the code.

The computed row contains System.DBNull.Value

causing the Rowfilter operation to retunrn DataView.Count=0.

Can you see what i'm missing?

Thanks