Invoking start process smart service and update constant smart service in Expression Rule

You can put the start process and update constant smart service function calls inside an expression rule, but that expression rule needs to be called within a!save() from a SAIL interface or from a Web API. docs.appian.com/.../Start_Process_Smart_Service.html

Hi Josh, my requirement is the expression rule has to be called in an parameter of an integration object and I cant use the SAIL interface here.

What are the higher level requirements? The documentation indicates it is not possible to call a smart service function outside of a!save() or a Web API so you will need to reconsider your approach.

Hi Josh, my requirement is to update a constant inside a expression rule and that expression rule to be called in the integration objects parameter. As i don't see any option to use Update constant smart service inside expression rule, we are using it in a process model and that we are trying to call in an ER. Ideally if there is a provision to call Update constant service inside ER that would suffice.

Hi rp_balaji I believe Web API is the best choice for you where you can invoke smart service function.

And you can invoke this Web API using integration object and you can call this integration object, where ever you want to (if it's a get call) using rule!

And you can try performing update constant operation with in the same process which you are trying to invoke using Web API, this should do your job.

Hope this will help you.

If you can expand on your specific use case, the community can provide suggestions that could help you out. Why are you trying to update a constant within an integration object? Are you trying to increment a counter to track how many times the integration object is called? Are you trying to retrieve data from an external system and update the constant's value with the retrieved data?

If you can expand on your specific use case, the community can provide suggestions that could help you out. Why are you trying to update a constant within an integration object? Are you trying to increment a counter to track how many times the integration object is called? Are you trying to retrieve data from an external system and update the constant's value with the retrieved data?

Hi Josh, Let me explain you my requirement,
We are calling a third party service through Integration object, we need to get OAuth token from a constant and pass it in the header of the request. For which we are using a expression rule to be called in the request header parameter, the expression rule will check the token expiry and if the token is expired it will call a third party service, gets the new token and update the same in the constant and return that token to be passed in header. This is the logic we are doing inside an expression rule.

Regards,
Balaji.R

Hi Balaji,

That makes sense. I have followed the design pattern that mentioned to achieve this in the past.

Depending on your circumstances you could also redesign the application to either A) Always get the OAuth token when making a request instead of caching it or B) Set up a process model that retrieves the OAuth token value, stores it to the constant, then sets a new instance to run when the token expires (In my experience when you grab the OAuth token it includes a field telling you when it will expire.)

Hi Josh,
Sure am revisiting my approach to modify it as Alokh suggested. And out of curiosity am asking this, may I know is there any specific reason from product perspective that they are not allowing to use any smart service in the Expression rule.

Regards,
Balaji.R

According to docs.appian.com/.../Expressions.html, "Expressions do not modify any data inside or outside the Appian system."