Create a View / Form use a Backend function as a source of information

chc

First, thank you for making this excellent platform available to us.

I would like to ask you if it is possible to create a view that can be used in a form or if a form can use a backend function as a source of information.

I have a table that houses a tree structure (organizational structure) and I need to present it in a list in a way that reflects that structure.

Thank you in advance for your kind response.

chc.

gabriel

Hello and welcome to the forum 🙂

It depends what you mean by a "view". A list or chart is technically a view and they have different display options and variations that can show or work with data in different ways.

You can use backend functions to get data and supply values to input fields on a form to filter other fields with (like lists) - we do this with apps like Tickets that uses a backend function to execute the global search to populate an input field to filter a results list. (Check the global search form in the Tickets app for an example)

But ultimately, you are limited by what our field types can display. I don´t think we can handle a dynamically sized tree structure (e. g. with unlimited depth) well with our current list fields.

chc

Thanks for the prompt reply.

Indeed, to solve the problem I have created a frontend function that calls a backend function that loads a table, initially empty, with the data I need. This function is then invoked on the before event of the form so that the data is available before the list is presented.

That should be enough for now.

Best regards,

chc

pd: REI3 is amazing!

dimitrios1988

chc How did you populate the list using a function? Using frontend function?

Martin

I am looking into a similar situation. I wonder if I could use REI3 to make user management in Nextcloud user friendlier.

Which means: I need to display a list of users and I need to open a form on click on a row to edit that list entry.

As I understand, I can not have a list in a form that is not bound to a relation and is populated via a function.

So the solution is to have "nextcloud_users" relation. A frontend function on form load triggers a backend function that fetches the list of users via REST-API from Nextcloud, truncates the "nextcloud_users" relation and populates it from the REST-API result.

Then also a similar frontend / backend function setup on edit form save to write-back the change to Nextcloud via REST-API.

To communicate errors in the REST calls to the user, you use instance.abort_show_message in the backend function.

Is that the way to do this?

gabriel

Martin
To do something like this, you would probably prefer for R3 to directly display external data sources - but you are right, currently you would need to sync data to a local relation (via REST preferably) and then work on that data.

instance.abort_show_message() is not helpful in this case however, because REST calls in backend functions are asynchronous - meaning they are executed on a scheduler and your function does not wait until you get data back.

For syncing data via REST calls in the backend, we´d usually execute calls regularly (like hourly) and then log errors either to the system log (log.error()) or to another relation, if we want to display it in the same app. Then current data (depending on the interval) is always available and errors are logged and visible after the fact.

Martin

gabriel

Thanks for the info, that is helpful. So if I want to ensure data seen and manipulated by the user is current, I would need to do the REST calls in the frontend (data size when moving data to the backend to put in the relation could be problematic).

Or not use instance.rest_call for the REST part in the backend and instead use some other way. If I can get the PL/Python extension working, it looks like I can then use something like described in https://stackoverflow.com/questions/46540352/calling-restful-web-services-from-postgresql-procedure-function

gabriel

Martin
Yes, frontend calls would solve that issue as you can wait for the response. Doing the call, sending that data to the backend, processing it, sending a response and then refreshing the form to show current data is quite a lot of steps though.

I´m often pleasantly surprised what people try to do with R3 - though we´ve never planned for use cases such as these, we´ll try to find solutions to make things easier.

Martin

Or, which would require some bigger changes on the organizational side of things: make REI3 authoritive for the user information instead of Nextcloud.