Hi,
I'm trying to test a fruitless foreach, and I'm surprised to see that the result is not just null or empty.- can you tell me why this code returns 20 null lines please (please see the attached file) ? I was expecting an empty list-
- In this case, how to assert that the result is fruitless ?
a!localVariables( /* Get a list of 20 Vehicles */ local!vehicles: a!flatten(rule!CJT2_GetVehiclesWithFilters( id: null ).data), /* The id = 550 does not exist in the Vehicles so we'll not find it */ local!oneVehicle: a!forEach( items: local!vehicles, expression: if(tointeger(fv!item.id)=550, fv!item, {} ) ), local!oneVehicle )
The object of this post, is not to replace foreach by another function (like index or reject) but to understand how works the foreach.
Regards
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The "flatten" function replies to my 2nd question... I can use it.
to reduce it to the core:{} =-> List of variant with 0 items .You exuted it 20 times so you get a list of variant with 20 items and each of them are a list of variants with no element.The moment you have no other element, its ignored and for example a car cdt structure is showna!isNullOrEmpty(local!oneVehicle) is still trueThis should solve your issue.
local!oneVehicle: a!flatten( a!forEach( items: local!vehicles, expression: if( tointeger(fv!item.id)=550, fv!item, {} ) ) ),
The nature of foreach() is to return a value for each item. This is exactly the reason why I strongly suggest to not use it for filtering.
Thank you for reply.I always use the "magic" flatten function.... but in my case I thouht the latter was used as a workaround.
that is the other topic: Why not using the queryfilter for the id in the query ? its the way better approach to filter.
stefan mentioned the general "design" issue with it. usually you have different options to filter way more efficient than with a!foreach.
Ok I understand the point, thank you Stefan
As I have mentionned Richard, I was not expecting to go further in this other topic.
My question was only about the "foreach" aspect (maybe I should provide a static set of data for my example ;-) )
I differ on this - other than the single corner case we see here where it returns an empty item for each iteration when all iterations are empty, having it spit back empty sets works just fine - and as long as you anticipate this behavior (which is funny tbh), a!forEach filtering can create much more coherent code than using primitive functions/looping.
Mike Schmitt said:a!forEach filtering can create much more coherent code than using primitive functions/looping.
For me what's missing is the ability in an if() or equivalent is to execute a NOP (No Operation) - that is, to opt to choose to output nothing at all. There have been many times where I have processed a list and then had to post-process the list to remove null values from it.