integrating your business

Yesterday we discovered something about the use of custom extension objects in custom XSLT.
Imagine that you need a counter value in your mapping. Since variables in XSLT can only be set once, you need to use custom code for this.
In our case we wrote a small helper class that has a counter variable.

public class Counter
{
    private int _counter = 0;

    public int GetCounter()
    {
       return ++_counter;
    }
}

I just called this in my map and tested it. It worked perfectly.

But then I fired a few concurrent calls to our BizTalk process, resulting in the map being executed multiple times in a very small time frame.
We noticed that the counter value wasn't correct anymore. After some analisys it seemed like the instance of the Counter class was shared over multiple executions of the map.
Our assumption that BizTalk creates a new instance of the class every time the map is called, was wrong.

We came up with a quite simple solution for this. Instead of just having 1 counter, we created a Dictionary that can hold multiple counter values.
The key for this Dictionary is a Guid (as string) and the value is the actual counter. Each map has it's own Guid that makes it unique.

public class Counter
    {
        private Dictionary _counter;

        public Counter()
        {
            _counter=new Dictionary();
        }

        public string NewGuid()
        {
            return Guid.NewGuid().ToString();
        }

        public int GetCounter(string guid)
        {
            return ++_counter[guid];
        }
    }

So this is how our class looks like with this Dictionary. At the top of your map you just create a variable that holds the Guid, and you use it every time you call the GetCounter method.

<xsl:variable name="Guid" select="Counter:CreateGuid()"/>

<xsl:value-of select="Counter:GetCounter($Guid)"/>

 We are still not quite sure how long BizTalk keeps this in memory. But to be sure we added a method to the class that deletes one row in the Dictionary at the end of a map.

 Tim D'haeyer, CODit