Dynamic function execution in Logic App

Question

Hello all,

I'm trying to simplify logical paths in a logic app, and being able to dynamically execute functions that are sourced externally (in my case, a CosmosDb). In an attempt to prove the concept out, I've used a simple date conversion function that resides in my CosmosDb.

So far I've tried putting curly braces on the content in Cosmos, and an @ sign, but have yet to find success. Could someone please elaborate on the proper way to perform this kind of action -> executing dynamic functions in a Logic App.

Kind Regards,

Jon

Compose Task Code:

        "Compose": {  

            "inputs": {  
                "Value": "@{body('LookupProcessConfig')?['value'][0].Function}"  
            },  
            "runAfter": {  
                "LookupProcessConfig": [  
                    "Succeeded"  
                ]  
            },  
            "type": "Compose"  

Cosmos Doc:

{

"ProcessName": "Dynamic FunctionTest",  
"Executable": "laDynamicFunctionTest",  
"ExecutableType": "Azure Logic App",  
"IsActive": true,  
"Version": 0,  
"Function": "convertFromUtc(utcNow(),'US Eastern Standard Time','yyyyMMddHHmmssfff')",  
"_shardkey": "laDynamicFunctionTest"  

}

Answer 1

Logic Apps do not allow parsing expressions at runtime, but there are options for doing something like this without complicating your workflow.

If you are on the new Logic Apps standard plan, then you get access to the Execute JavaScript action which is still in preview. While Logic Apps doesn't allow you to evaluate code dynamically, JavaScript does.

I added a Parse JSON action to my version just to make the expression a little simpler, but basically the code boils down to return eval(<string retrieved from cosmos>)

The second option would be essentially the same but leveraging Azure Functions. It's quite a bit more cumbersome, but it works on the Logic Apps consumption plan and you have more language options if you don't want to utilize JavaScript.