SCOM Script Monitor Numeric Expressions Default To String

Here's a straighforward explanation of something I found took me a long time to figure out. I found lots of posts but none that explain this straight up...(also I'm sure I knew this 5 years ago when I was doing heaps of SCOM stuff but had since forgotten!)

If you make a SCOM scripted state monitor using say a vbscript and you want to check the result of a numeric value (say an integer), by default it does a string comparison not a numeric one.

Regardless of the variant type your script produces (note variant types listed here: http://www.culham.net/2012/scom/property-bags-and-variant-types ) the authoring gui's create a STRING type compare. This is because there is no datatype field on the SCOM editing screen (unlike say CA Spectrum event configuration where every value has to be typed explicitly).

For example say I return this with my MOM.ScriptAPI AddValue("diffThresholdMinusRun",iServiceCountThreshold-good)

this results in something like:
<DataItem type="System.PropertyBagData" time="2014-04-04T12:09:26.8984174+13:00" sourceHealthServiceId="2B60ADC4-15C5-0FE3-7FF8-1"></Property><Property Name="diffThresholdMinusRun" VariantType="2">-1</Property>...

Now I create a unhealthy expression in SCOM for >0 critical and <=0 OK. Unfortunately the comparisions default to STRING so don't work properly. Any negative value is evalutated as unhealth (becuase - is > 0 in string compare) For example

       <ErrorExpression>
            <SimpleExpression>
              <ValueExpression>
                <XPathQuery Type="String">Property[@Name='diffThresholdMinusRun']</XPathQuery>
              </ValueExpression>
              <Operator>Greater</Operator>
              <ValueExpression>
                <Value Type="String">0</Value>
              </ValueExpression>
            </SimpleExpression>
          </ErrorExpression>

The only way to fix this is to edit the management pack xml (in the 'edit' screen in authoring console or in xml editor) so that it has a valid numeric type (say Integer).

 <ErrorExpression>
    <SimpleExpression>
      <ValueExpression>
        <XPathQuery Type="Integer">Property[@Name='diffThresholdMinusRun']</XPathQuery>
      </ValueExpression>
      <Operator>Greater</Operator>
      <ValueExpression>
        <Value Type="Integer">0</Value>
      </ValueExpression>
    </SimpleExpression>
  </ErrorExpression>