What will Power Fx mean for Model-driven Power Apps?

By now many of you will have read about the announcement Microsoft made at Ignite 2021 on their “low-code programming language for everyone”. I’ve written about the wider role of Power Fx in the high level Power Platform story in the Forward Forever team blog, which will give you all the basic information on what/why/how/when:

Recently I also recorded a quick 10 minute video discussion I had with Julie Yack from 365.training where I had a chance to verbally express some of my thoughts on Power Fx:

I’ve personally started my low-code journey with Microsoft Business Applications back when the concept of XRM was first promoted, which is why most of my hands-on experience with Power Apps lies firmly on the Model-driven side. Power Fx as a formula language originates from a time when the two app types (Canvas & Model-driven) were still completely separate product offerings. If you’ve always built Canvas apps, there’s essentially nothing new for you in Power Fx. If you’ve only worked with the Model-driven business apps (Dynamics 365), there will be plenty of changes ahead.

In this blog post I’ll share some initial thoughts on how I see the arrival of Power Fx potentially affecting the way Model-driven Power Apps are built.

Why Model-driven needs Power Fx

There has traditionally been a clear divide between no-code and pro-code tasks when building apps the XRM way – meaning customizing and extending Dynamics 365 Customer Engagement apps in most cases. You’ve had a GUI for clicking your way through a variety of configuration options the application platform offers, to perform tasks like:

• Define entities, fields and relationships
• Determine the layouts of your forms, sitemaps and views
• Design business logic via workflows, business rules, BPF

Our reliance on the almighty mouse pointer as the sword with which we fight our way through a battle field full of fierce business problems might be considered a weakness. Sure, we’ve often managed to emerge as the no-code hero who’s been able to tackle a business requirement most bystanders would have expected to require custom code. Yet there’s frequent frustration to be experienced when the particular configuration option we would have needed was not present in the graphical user interface (GUI).

Such problems don’t need to be very complex to become unsolvable. All it takes is for the specific function to have fallen outside of the scope of features that the Microsoft product team has managed to squeeze into the platform’s built-in toolkit. Sometimes you might find a community tool that generates the required JavaScript for you, or a custom workflow activity comes and extends the built-in actions to let you implement that specific calculation your customer needs.

Yet it remains mostly a black box for the non-pro developers: the next time you run into a similar limitation, you’re likely to again need help from the pro-devs to move forward. Venturing beyond the GUI tends to always push us into uncharted territory.

What the announcement of Power Fx promises is far more empowering. “Formula based Power Apps Model-driven customizations” sounds like you could actually get a peek of the underlying logic layer in text format rather than a finite list of picklist options to choose from. At the same time you probably would not need to assume responsibility of any software code implementation details. The lower level of how the conditions defined by your formula are actually met by the big computer running in the cloud would not be your concern.

This aligns with the promise of declarative programming:

The maker describes what they want their logic to do, not exactly how or when to do it. This allows the compiler to optimize by performing operations in parallel, deferring work until needed, and pre-fetching and reusing cached data.

Power Fx documentation on the language’s design principles

For me, the big reason to steer clear from copy-pasting JavaScript snippets from websites and tweaking them to be used in business applications built for customers is that I’m all too aware of what I don’t know. While I can often read what the specific scripts are doing, I don’t fully understand why they work vs. why they would not work under different circumstances. It would be far too easy for me to accidentally create something that breaks in the near future – not because of a bug in Microsoft’s code but a bug in my code.

Formulas that are written in Power Fx (today only in Canvas apps) are very different. Sure, they can be very complex as well, but there’s no knowledge required from outside the domain of Power Apps. If I pick a tutorial video from Shane Young’s YouTube catalog that explains the usage of a particular function in Canvas apps, most of the time I get it. I can immediately adapt it for my own scenarios, and get helpful Intellisense error messages from Power Apps Maker Studio when there’s something missing from my function (well, not always helpful messages, but at least an indicator of “keep trying”).

Taking the step to writing your Power Fx formulas instead of just clicking around the GUI helps in unleashing your creativity in app design and significantly expanding the realm of what’s possible. There’s also big potential in improving the efficiency of the app building process when you can copy-paste text based formuals instead of having to repeat a series of clicks in the MS admin portals that seem to only get slower and slower as years go by…

Why Power Fx may be scary for Model-driven app makers

Canvas apps have been promoted as the way to create “pixel perfect experiences” tailored to the end users’ specific requirements and needs. This is a completely different starting point for low-code app creation than the traditional business apps in CRM style projects where you are mostly customizing an existing application. On a high level, everything will look & behave pretty much the same way every time.

I’d argue that many of the limitations in Model-driven apps are in reality a safety net for the no-code app makers. Back in 2019 I did a presentation on the topic “Canvas apps for the Model-driven mind”, which describes the kind of leap that is needed both on mental and practical level for an XRM pro to turn into a modern Power Apps app maker. Power Fx will now play a big role in this transformation.

The relational Dataverse data model that sits behind every Model-driven Power App largely dictates how the app UI will function. As a result, there’s not too much creativity required nor allowed in creating the visual side of your business application. Navigation and Command Bar buttons will be generated for you, and you can rely on them being constantly presented to the user. Everything’s responsive out of the box, too.

The other side of Power Apps that’s not built on relational data structures and predefined UI grids is the world where everything runs on Power Fx. In Canvas apps the buttons don’t exist until you drop them on the screens and they do absolutely nothing until you add a piece of Power Fx text into the OnSelect property. Any dynamic behavior that’s desired for the app’s controls (visibility, size) must be expressed in Power Fx for their respective properties.

Building Canvas apps doesn’t require you to have programming skills, but it does quickly push you much closer to the experience of custom app development. You’re no longer merely a system customizer like in Dynamics 365 scenarios, now you’re an app maker. The whole purpose of the low-code tooling is that it blurs the lines between traditional developer roles, thus powering the new “fusion teams” that may share many of their tools – and now also the programming language.

As a result, it becomes less obvious what you can & can’t do without custom code extensions when building Power Apps. Configuration expressed as text based formulas can be vastly more powerful than GUI based options, allowing the most creative makers to achieve functionality that others might assume to be impossible with the available tools.

Journey towards “just Power Apps”

Back in Summer 2019 Microsoft revealed their long term roadmap on how the two types of Power Apps would eventually converge into one. We haven’t yet seen much concrete changes on how Model-driven and Canvas could coexist within a single app, apart from the embedding feature. The original plans for launching custom pages as a “canvas” within Model-driven apps were removed from 2o20 release wave 2 and no new target dates have been announced for it.

There is likely a wealth of moving parts in this puzzle that have dependencies between each other, so it’s no wonder this merging of Model and Canvas apps is taking time. Power Fx is a clear step towards making the new app building story consistent. Plenty of new functionality is likely to be needed, though, as you’re not simply replacing one programming language with another. Rather it’s the case of expanding bespoke GUI tools with a low-code programming language that can also be used to express the same logic.

Exactly what the new Power Fx based “form and commanding customization in Power Apps” promised at Ignite will consist of remains to be seen. Calculated columns defined with Power Fx are much easier to grasp. The same goes for the conversion of Business Rules into Power Fx formulas, since already today the Text View in the editor looks a bit like these.

Making that If-Then-Else box editable would be a simple step. However, turning the actions in Business Rules into something that you could define with Power Fx and apply on a Model-driven form will surely require some more platform unification work. Show/hide fields, set required, prompt for errors… They all sound straightforward from a logic perspective, but how will such concepts be extended to cover not just Canvas sceen controls but Model form controls is going to be interesting to watch.

This is probably why Business Rules are in the same “future roadmap” bucket as the Power Automate flows for receiving Power Fx coverage. It’s not yet easy to envision how the declarative logic of Excel that Power Fx tries to follow wherever possible is going to be applicable to these more imperative scenarios. What would a flow written in Power Fx look like and is it really going to be easier for app makers to grasp than the current GUI?