A couple of weeks ago I found an empty slot in my diary, and I (dangerously) thought “I know, I’ll brush up on my Canvas app skills!”.
In my role I find myself looking across multiple Dynamics 365 apps, Excel spreadsheets, and Power BI reports daily, and I set myself the task of bringing all of this together into one place so that I could access all of the data I need with one or two clicks instead of manually transforming data and keeping several browser tabs permanently open.
This was going great, until I saw the dreaded ‘delegation’ warning that all Canvas app novices will see very quickly in their career.
“Delegation warning. The Filter part of this formula might not work on large data sets.”
When you expand the warning, you get the following detail:
What is Delegation?
Simply put, delegation is an instruction from the target application to the data source, to carry out a query before returning the subset of results that are wanted by the target application itself.
This means that we only ever receive the desired data in the target application, and in turn, performance is increased as a result.
When you compare the processing required in this scenario compared to retrieving every piece of data and then filtering it in the target application, you see a measurable performance increase by using delegation, and you’re also increasing technical debt by pulling back data into the target environment that you want to throw away immediately.
The wording for this warning can be considered a little misleading. The warning is actually telling us that there will be a lack of delegation in the data source. In this instance, the data source does not have the ability to carry out the condition logic with its capabilities, and therefore it needs request that the Canvas app carries out the query instead.
For example, Power Fx provides the ability to retrieve a day, month, or year value from a Date field, but Dataverse cannot do this! Dataverse can only query date ranges such as ‘on or before [Date]’! When querying a ‘month’ in this scenario, you would receive the delegation warning as the delegation cannot happen.
As a result, the full data set from the data source has to be retrieved by the target application, only for the target application to filter the data once it has all been received. This lowers the performance of the app, but it could be worse than that – if you exceed the definition of ‘large data set’, the data set may not return at all, leaving you with incomplete results with no error and a low quality solution.
The biggest lesson learned whilst working on delegation recently was from a colleague – there is always a workaround.
Whilst you can’t “fix” the warning with the same piece of code, you can use combinations of delegated conditional logic in order to achieve the same results.
A classic example steps back into using dates in Canvas Apps. In Power Fx I can express “Month = 1”, but Dataverse only allows date ranges so the Canvas App needs to bring back the full data set to work out whether “Month = 1”. As a result, I can’t quite express “in January this year” using delegated logic, so instead I need to combine two ranges using something that Dataverse can recognise. In this example I would combine “Created On must be on or after 1st January 2021”, and “Created On must be on or before 31st January 2021” to obtain the right data at source.
Some examples can be more complicated than this, but a top tip for Dataverse specifically is that if you can achieve it using Advanced Find, then you can be certain that the logic can be delegated!
Have you worked in this space before and found any cool workarounds? Leave a comment below!
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