Extracting max value in GridView column in a Web Performance Test - asp.net

Question

This pertains to .NET Web Performance Tests.
If I have an ASP.NET page with a GridView that has a column of ints, how do I write an extraction rule to get the largest int in the column?
I tried creating a custom extraction rule by inheriting from ExtractionRule and in the Extract method using e.Response.HtmlDocument.GetFilteredHtmlTags however, the HtmlTags returned don't seem to expose their innerHtml contents.

Answer 1

Perhaps you can write an extraction rule that gets the whole column, then process the numbers to get their maximum value. Alternatively, use a built-in extraction rule to get the whole column, then write a plugin to get the maximum value. In either case your code should expect a mixture of numbers and other text.

Answer 2

Ben Day has a great blog post containing two types that express similar concerns. TableColumnValueValidator and ExtractRandomValueFromTable.
http://www.benday.com/2013/08/19/validation-extraction-rules-for-visual-studio-2012-web-performance-tests/
In the Extract(object, ExtractionEventArgs), you need to parse the ExtractionEventArgs.Response.BodyString. Ben uses the HtmlAgilityPack library for this. http://www.nuget.org/packages/htmlagilitypack
Something like this is roughly the code you'd need. This is simliar logic to ExtractRandomValueFromTable.
This does not account for thead/tbody or cells that span multiple columns/rows.
HtmlDocument doc = new HtmlAgilityPack.HtmlDocument();
doc.LoadHtml(e.Response.BodyString);
HtmlNode table = doc.GetElementbyId(TableId); // TableId is a test property
HtmlNodeCollection columns = table.SelectNodes("//th");
int columnIndex = FindColumnIndexByName(columns, ColumnName); // ColumnName is a test property
HtmlNodeCollection rows = table.SelectNodes("//tr")
int maxValue = Int32.MinValue;
foreach(HtmlNode row in rows)
{
HtmlNodeCollection cells = row.SelectNodes("./td");
// Todo check for bounds of cells here
HtmlNode cell = cells[columnIndex];
int value = Int32.MinValue;
Int32.TryParse(cell.InnerText.Trim(), out value);
maxValue = Math.Max(value, maxValue);
}
e.WebTest.Context.Add(ContextParameterName, maxValue);
int FindColumnIndexByName(HtmlNodeCollection columns, string columnName)
{
for(int i=0; i<columns.Count; i++)
if (String.Equals(columns[i].InnerText, columnName, StringComparison.OrdinalIgnoreCase))
{
return i;
}
return -1;
}