Good morning,
Okay now I got a picture.
Let me come to your first question.
It is making a difference if you are using SPO or SP onPrem, cause you would need to establish a connection to your onprem environment via a gateway to fetch data from your SP onPrem. With SP Online you can directly call the SP REST API without entering any firewall secured environments.
But its good that we are talking about SPO!
I also now understood your usecase.
I would say that Power Automate is the wrong technology for your usecase.
I will explain later why I think its not the best idea, but first I would try to show you my idea how
I would build this if I needed to.
So if you want to create this with Power Automate I would concider to do the following:
I would create a flow that will represent your API, you would start with a request trigger (https://flow.microsoft.com/fr-fr/blog/call-flow-restapi/) so your flow gets an rest endpoint.
The trigger is a post endpoint and you can define your JSON Schema. I would give the endpoint the name of your "function" (eg. getallpos or getpos or something else) so the flow knows what to do.
Now you could call your SharePoint lists to fetch the data based on the info you get from the trigger body.
You would need to to some merging operations to build a json that can be send back to the requester.
So you might need some foreach loops etc. It could look like this:
Now you could save the flow and call the endpoint to get the data you requested.
This is working, buuuuut... we have some problems here.
So first the loops inside the power automate are reeeeeally slow. So when you start to merge data from different SharePoint lists and parse your json manually, it will tak you ages for big datasets (lets say bigger then 250 items) So it might happen that your client will run into a timeout when calling the rest endpoint of your flow. In addition your client would need an power automate licensed account. And I am not talking about the E3 lisences, I talk about the per Flow or per User plan.
So all together, yes it is possible, but its not having a good performance and its expensive.
So what are your alternatives?
1. A custom connector itself cannot help you, cause its is not possible to give a custom connector logic, which would give you data from differrent lists at once.
2. Another posiblity is to do this in Azure with a logic app (https://docs.microsoft.com/de-de/azure/logic-apps/logic-apps-overview). Its technically the same. The difference is that you do not need a power automate licensed account in order to call the flow. The performance is still bad (maybe it could be better cause you could use javascript to process your sharepoint items parsing a json), but you could have this at least less expensive.
3. So the cleanest way to implement your a good solution for you would building your own web api. So I would consider doing it with Azure functions. https://docs.microsoft.com/en-us/learn/modules/build-api-azure-functions/ You could easily build up your logic inside the function and then make the endpoint available for your client. This would be clean, not expensive and the performance is much better.
Let me know if my answer was clear or if you need any further assistance on the other topic, cause we are leaving the power automate scope here.
With regards
Kevin
