Conditional Display in a Datalist

Colonel Angus · December 16th, 2004, 09:30 AM

I need to display data conditionally in one of my datalist columns.

Code:

<asp:TemplateColumn>
    <ItemTemplate>
      <%#Container.DataItem("retVal")%>
    </ItemTemplate>
</asp:TemplateColumn>

If retVal is a certain value, I don't want to display it. I tried using an if..then structure, but it errored out.

Thanks in advance for your comments.

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In God we trust, everything else we test.

stu9820 · December 16th, 2004, 09:34 AM

Is retVal coming from a database? You could exclude it from your SQL.

Colonel Angus · December 16th, 2004, 09:38 AM

Good point, Stu. I'll give that a try. However, I am still curious about the possible datalist technique.

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In God we trust, everything else we test.

Imar · December 16th, 2004, 09:39 AM

You can add a function to the Code Behind file that examines the state of the object and returns whatever it is you want it to return:

Code:

public string TestValue (object myValue)
{
  if ((string) myValue == "Some Value")
  {
    return "":
  }
  else
  {
    return (string) myValue;
  }
}

You'll need to change the ASPX file accordingly:

<%# TestValue (Container.DataItem("retVal"))%>

HtH,

Imar
---------------------------------------
Imar Spaanjaars
Everyone is unique, except for me.

Colonel Angus · December 16th, 2004, 09:46 AM

Thanks, Imar - that did the trick!

Also, Stu...I gave the SQL solution a try, but without entirely excluding the entire record the technique would have been trouble.

Thanks to you all again!

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In God we trust, everything else we test.

Imar · December 16th, 2004, 09:48 AM

Oh, one more thing.

If the database returns a null value, you'll need to compare your value in the function against DBNull.Value

Cheers,

Imar
---------------------------------------
Imar Spaanjaars
Everyone is unique, except for me.

planoie · December 16th, 2004, 05:48 PM

Colonel,

For future reference....

You can embed some field condition logic in the SQL statement:

SELECT field1, field2, CASE field3 WHEN 'somevalue' THEN '' ELSE field3 END as field3 FROM sometable ...

mehdi62b · December 17th, 2004, 05:17 AM

Hi there,
IMO,you could fetch all rows and then use DataView.RowFilter Property,then if you need again to change your condition,you wont need another hit to your datasource,

Code:

dv.RowFilter="retVal='Value1'";
//Rebind your datalist

_____________________________
Mehdi.
software engineering student.
Looking for a good job for summer 2005.

planoie · December 19th, 2004, 02:04 AM

mehdi,

Your point about using the DataView.RowFilter property is valid however it's somewhat impractical. With nearly all designs I've seen, the datasource (DataSet or DataTable) is not persisted across page hits because it is a very inefficient use of server memory (and introduces the problem of stale data). In all the ASP.NET applications I have constructed, whenever there is a change to the criteria for data, I requery the database, thus letting the DB engine perform the filtering of the data resulting in less data being returned over the database connection to the web server.

In addition, I think the original posted was implying that only a certain column's value should be suppressed if it meets a given condition. For this, RowFilter is of no use because it will hide the entire row.

mehdi62b · December 19th, 2004, 10:36 AM

I didnt write how we should persist data among several requests in my previous post(putting to cache is one of the ways),
however something I told not suitable for all situations,for example,
suppose we have a site doesnt change very much,also it could have many users hitting it every day,(like a page(grid) informs beautiful final exam grades(!),and suppose every student could sort it and find(filter) his grades)in my opinion using cache in such sites is the best choice,it could improve the performance of such sites very well ...

Quote:

quote:I think the original posted was implying that only a certain column's value should be suppressed if it meets a given condition. For this, RowFilter is of no use because it will hide the entire row.

if original poster wants that,he could use Imar's method(however,instead of showing a "" row we could hide it).

_____________________________
Mehdi.
software engineering student.
Looking for a good job for summer 2005.