Allow filtering a list by Rule

Question

Allow filtering a list by Rule

18

Currently, if you want to filter a list on a more complex condition than can be expressed in a simple expression, you are bound to either:

manually iterate the list and keep a reference to the object, if it is found, through a custom NPE with an association to that object, or
walking over the list recursively using Head and Tail operations and a submicroflow invoking itself, risking a StackOverflowException in case the list would become too long.
[Edited:] creating a new empty list, add a found object to that list within the loop, and process the result afterwards

This is a proposal to allow filtering a list on a Rule. The Rule gets the list element as its only parameter. If it returns true then the element is accepted, otherwise it is rejected.(*) This way, we can build much more powerful filters and keep the model readable at the same time.

(*) A Rule can also return an Enumeration value. This would either be disallowed, or we could allow to filter on the rule result being equal to some expression.

asked 2020-04-15

Reinout van Schouwen

2 answers

Jeroen Huizer · Answer 1 · 2020-06-11

Great idea!
Alternatively, allow expressions in the find/filter. That would allow you to compare against values from the context.

Something like:

$currentObject/Age >= $MinimumAge and $currentObject/HasDriversLicense

Conner Charlebois · Answer 2 · 2020-04-15

This is a wonderful idea, and should also apply to “find” operations