Canvas Apps, Patch command, & Business Rules

Recently I’ve been doing a LOT of work with canvas apps. As I think I’ve mentioned before (at least once or twice!) my background is the traditional ‘model’ style app. As a result, it’s been quite a steep curve to skill up, but I think I’m handling it alright. I’m (slowly) getting used to the way that canvas apps work, the ability to put different controls on the screens, and reference each other.

Heck, I’m even starting to play with more advanced navigation concepts, based on some REALLY great ideas that I’ve seen (Clarissa, I can’t say how grateful I am to you for all of your assistance & guidance!).

Amongst all of this incredible & wonderous journey, I’ve also been learning some code. Yup – you heard me correctly! I’ve always said that I’m not a developer – I respect them greatly, but I don’t develop code.

True, I’ve picked up some SQL here & there, and will freely admit that running SQL queries against the Dynamics 365 database is SO much more powerful than running an Advanced Find. Of course, it’s necessary to know the joins, conditions & such. Redgate’s SQL Helper has been amazing along the way. With moving to cloud systems, things got a little more….complicated. XrmToolBox has the SQL4CDS tool which I’ve used several times, but I was really excited by the recent announcement/release of being able to (properly) run SQL commands against the CDS database from SQL Management Studio….

Anyhow, I’m digressing. So, I’ve been needing to learn canvas app style code. It’s like Excel commands, though (slightly) different at times. Things don’t always make sense (to me, at least) – I STILL haven’t figured out why some expressions need to be in a certain order. After all, according to mathematical principles it doesn’t matter if you write A>B, or B<A. Going to still need to wrap my mind around all of this.

So, one of the commands that I’m using quite frequently is the Patch command. If you’re really interested, you can check this out in detail at https://docs.microsoft.com/en-us/powerapps/maker/canvas-apps/functions/function-patch.

In short, Patch allows you to set record values from places other than a form table to the data that you’re saving. It also allows you to save field values that aren’t available on the canvas form table (due to limitations). I’ve referred to this previously at https://thecrm.ninja/canvas-app-record-set-regarding-field/. The scenario that I talk about there is just one of the things that can be done in this way. Since that post, we’ve come a long way, and are doing most things with Patch statements (due to the scenario requirements).

So that’s all well & good. However, there IS actually a reason for me writing this blog post….crazy, right? And it’s not to waffle on and on about patch statements. It’s about a very specific scenario that we hadn’t come across to date, but that came up last week.

Now, obviously you’re now VERY interested in hearing all about it, and learning for your own situations. I mean, otherwise you wouldn’t have stuck with me through this article for so long. So, let me set out what happened.

As mentioned above, we’re mostly using patch statements throughout this specific app. That’s….quite a lot of patch statements (especially as we also have IF statements governing which one is being used, as it’s not possible to use IF inside a patch statement, but I’m digress…). I’d say we’re pretty familiar with this now.

However, even with being familiar with it, we suddenly had a problem. One of the forms that we’re saving down started to NOT save down. Records weren’t being saved, which obviously is a problem!

Bear in mind here that we hadn’t touched the code for this specific action for a few weeks. Nothing had changed in our code, and nothing had changed from a platform perspective (ie Microsoft hadn’t changed any of the underlying functionality.

Going into the statement, we immediately started testing it out, and saw something interesting. We were getting an error that a required field could not be NULL:

This was quite puzzling – although in a model app we can set fields as required, and users can’t save the record until they populate it, this isn’t true in a canvas app (well, when using Patch, at least). See, it’s technically possible to use a Patch statement to create/update a record, but you don’t have to pass in required field (values). It’s a sort of workaround (& can be used in some scenarios for benefit, actually). So this happening all of a sudden was quite strange to us.

It was even stranger as we hadn’t been using the field on the form at all. The field that was being referred to was being used for a totally different process, in a different team, & not surfaced into the canvas app at all. This really was causing us to scratch our heads, and try to think (more) out of the box. It didn’t seem to be the code (we could set a value in code, but didn’t want to as it wasn’t relevant), yet we weren’t able to ignore it. Really frustrating!

With all of this in mind, I decided to go back to absolute basics after a few hours of troubleshooting. The field that seemed to be causing all of these issues was a relatively new addition, so I checked all of the details around it:

• Was the field type correct for what it should be? Yes
• Was it set as required on the CDS field definition? No (not that I thought this would help, but still checked)
• Was the field on the entity form? Yes
• Was the field set as required on the entity form? No (again, I didn’t think I’d get any joy from this)
  • Hold on….on the form designer it’s not set as Required. But when I open the form, and put some values in, suddenly it IS required.

Aha! OK – I’m now starting to see some light shining on this. I headed over to Business Rules to check out what might be there. Lo & behold, there was a business rule that set the field as required (when certain conditions were filled). An example of this would be:

Now this field hadn’t been in place when the code was developed (as mentioned above) – it had come in since. I was very curious if a Business Rule could require canvas apps to set the value, and so did some testing.

Disabling the business rule removed the error from the patch statement. Re-enabling it caused the issue again. OK – so we’ve found what’s been causing this, and could put in an adequate solution to handle it.

So in short, if you’re setting a field as being required through a Business Rule, you’re going to need to address it in any canvas app as well (that’s saving data down to the same form that it’s appearing on). Why it actually happens, when just setting it as Required on the form doesn’t, I have NO idea.

But it’s a good concept to keep in the back of your mind, I believe. Especially if there are multiple people working on developing a single entity, as otherwise you could find yourself in exactly the same scenario that we did!

Have you come across anything like this, or a different piece of strange behaviour? Comment below – I’d love to hear about i!