Capture partial value from JSON payload

[ravivish83]

In the JSON payload like below, I have to capture "severity": only '4' digit value but ExtractVariables gives Sev4 , and which 4 digit value needs to be sent to other JSON pay load via <Set> <Payload contentType="application/json" variablePrefix="@" variableSuffix="#">

{
  "schemaId": "azureMonitorCommonAlertSchema",
  "data": {
    "essentials": {
      "alertId": "/subscriptions/000000",
      "severity": "Sev4",
      ...
    }
    ...
  }
}

So is there a way to capture the partial value and save it to the parameter for passing to another JSON 

[dchiesa1]

I guess you are using something like this in ExtractVariables, to get the severity field:

<ExtractVariables name='EV-Severity'>
  <Source>azureResponse</Source>
  <VariablePrefix>extracted</VariablePrefix>
  <JSONPayload>
    <Variable name='severity'>
       <JSONPath>$.data.essentials.severity</JSONPath>
    </Variable>
  </JSONPayload>
</ExtractVariables>

And as output of that, you have the context variable extracted.severity holding "Sev4". And what you want is just "4".

JSONPath doesn't have a way to express the idea that you want a substring. With JSONPath, You can extract a field or a set of fields, but not a substring of a field. So you must rely on a "post processing" step to get the substring. Probably in Javascript, just use a call to the substring function.

Your logic will be like this:

1. ExtractVariables with JSONPath (as above)
2. JavaScript policy that uses substring

The JS code will look something like this

var s = context.getVariable('extracted.severity'); // variable set by ExtractVariables policy
s = s.substring(3,4)
context.setVariable('single-digit', s);

You can also get substrings via message templates, in AssignMessage: 

<AssignMessage name='AM-Substring'>
  <AssignVariable>
    <Name>three</Name>
    <Value>3</Value>
  </AssignVariable>
  <AssignVariable>
    <Name>four</Name>
    <Value>4</Value>
  </AssignVariable>
  <AssignVariable>
    <Name>single-digit</Name>
    <Template>{substring(extracted.severity,three,four)}</Template>
  </AssignVariable>
</AssignMessage>

It's weird that you need to use variable names (three, four) for those fields, but that's the way it works today. 

[ravivish83]

Resume back on it. 

Thanks for the solution. It works as expected.

[dchiesa1]

👍

Thanks for the confirmation.