PLEASE NOTE: There is an updated article which explains how to use direct calls from a Power App using Custom Actions instead of Power Automate Flows. This is a much simpler and more performant way of achieving the same result. See the details here: https://support.north52.com/knowledgebase/article/KA-10514-dynamics-crm-365-xRM-Formula-284-Complex-rules-in-Canvas-Power-App-using-direct-Custom-Action-call/en-us

Overview

Complex rules are often required to be executed as part of a Canvas Power App. North52's business rules engine for Microsoft Dynamics 365 and the Power Platform is a perfect partner when you need to evaluate complex rules in a Canvas App.

In this article, we will use the example of calculating a risk score for Coronary Heart Disease via a Canvas App. The rules and Decision Table structure for the calculation have been outlined in a previous article where the calculation is being made in a Model-Driven App.

This example shows how stateless processing can be used with North52's business rules engine.

 

https://www.youtube.com/watch?v=Bj2n1lkkrY4

 

Rules for Calculating Coronary Heart Disease Risk

Please see the previous article for the rules table.

North52 Decision Suite Solution

The North52 Decision Suite solution works like this:

• A Custom Action is set up with one input and one output parameter
• The Custom Action is triggered from the Canvas App via a Power Automate Flow
  • The Canvas App passes data from the App to the Flow
• A Formula is set up on the Custom Action which:
  • Takes the data from the Canvas App
  • Evaluates the data using risk criteria on several Decision Tables
  • Returns results of the Risk Score as JSON
• The JSON is returned to the Canvas App via the Flow and converted into a Collection 
  • The data from the Collection is used to display the Risk Score and Messages on the Canvas App 

Set up Global Action, Formula, Flow and Canvas App

There are 4 parts to configure for this example: Global Action, Formula, Power Automate Flow and a Canvas App.

Global Action

Set up a Global Action with two parameters:

• PayloadInRiskParametersJSON
  • Type = String
  • Direction = Input
• PayloadOutRiskResultsJSON
  • Type = String
  • Direction = Output

Formula

For details of how to construct the evaluation criteria for the risk score see the xRM Formula #161 - Coronary Heart Disease Risk Score article.

The major differences for this example are:

• The Formula is of Type Action
• Source Entity is N52 Command
• JSON is parsed on the Global Calculations sheet
  • These values are used on the Decision Sheets evaluating the risk
• The Risk Score and Messages are output to the Action parameter PayloadOutRiskResultsJSON

Formula Type

• The Formula is of Type Action bound to the Action Event n52demo_HeartDiseaseRiskAction
• First Decision Sheet calculating the Smoking risk is shown below:

Global Calculations Sheet

• The Global Calculations sheet maps values from the PayloadInRiskParametersJSON input parameter to individual calculations that can be easily referenced in the Decision Sheets (like the Smoking one above)
• Firstly the PayloadInRiskParametersJSON input parameter is assigned to the North52 internal variable called responsecontent
• Then individual values are assigned, for example, Current Smoker is assigned on row 4 

Risk Calculation Sheet

• Column J is an incremental inline calculation
• Column K is an inline calculation that calls a parameterized Global Action (see next image below for details)
  • The highlighted cell K4 shows the BuildJSON Global Action with the first parameter 'Smoke Risk' and the second parameter 'The patient has a smoke risk.'  

BuildJSON Global Action

• The BuildJSON Global Action shows how we are constructing JSON to collate the messages for each matching risk

• An example of the output for this Global Action:

  {
    "risktype": "Smoke Risk",
    "message": "The patient has a smoke risk."
  }

Action Response Sheet

• This sheet provides the response to the Action's PayloadOutRiskResultsJSON output parameter
• The highlighted contents of cell A4 shows construction of the JSON, including the Risk Messages JSON from above

• An example of the output for this output parameter:

  {
    "Results": {
      "RiskScore": 3,
      "RiskMessages": [
        {
          "risktype": "Smoke Risk",
          "message": "The patient has a smoke risk."
        },
        {
          "risktype": "Dyslipidemia Risk",
          "message": "The patient has a dyslipidemia risk."
        },
        {
          "risktype": "Family History Risk",
          "message": "The patient has a family history risk."
        }
      ]
    }
  }

 

Power Automate Flow

The Power is relatively simple with just 3 steps:

• Trigger from PowerApps
• Perform an unbound action - this connects to our n52demo_HeartDiseaseRiskAction Action
  • Assign the output from the Canvas Power App to the PayloadInRiskParametersJSON input parameter 
• Response
  • Set the Body to the output from the previous step: PayloadOutRiskResultsJSON
  • Create the Response Body JSON Schema from sample JSON - this can be easily obtained by running the Flow and analysing the results
  • NOTE:  do not use the Respond to a PowerApp or flow step as this will return the JSON to the Canvas Power App as a string and cannot be added directly to a collection in the Canvas Power App

Canvas App

Within the Canvas App there are two important parts to review:

• The OnSelect property of a button to collect the values and submit them to the Power Automate Flow
• The DataTable which shows the messages that have been returned as part of the JSON response

OnSelect of Button

• The values from many input objects are collated in a Collection called FormulaData (1)
• This FormulaData Collection is passed to the PowerApp->CallNorth52HeartDiseaseRiskAction (2) Power Automate Flow as JSON (3)
• The Flow returns the Results (4) and adds this to another Collection called RiskScoreResults
• The property RiskScore (5) is obtained from the RiskScoreResults collection

DataTable

• A DataTable is shown using the RiskMessages property of the RiskScoreResults Collection