Ash Elixir•2y ago

Composing filter expressions

I'm trying to figure out how to reuse/compose (eg. apply a not) a complex expression that I use in filters. I have a complex filter expression that looks like this:

    read :get_processed_for_visit do

      filter expr(
               not is_nil(visit.processing_started_at) and
                 summary_processed_at(is_nil(false)) and
                 summary_processed_at > visit.processing_started_at
             )
    end

    read :get_processed_for_visit do

      filter expr(
               not is_nil(visit.processing_started_at) and
                 summary_processed_at(is_nil(false)) and
                 summary_processed_at > visit.processing_started_at
             )
    end

and then another one that is:

    read :get_unprocessed do
      filter expr(
               not (not is_nil(visit.processing_started_at) and
                      summary_processed_at(is_nil(false)) and
                      summary_processed_at > visit.processing_started_at)
             )
    end

    read :get_unprocessed do
      filter expr(
               not (not is_nil(visit.processing_started_at) and
                      summary_processed_at(is_nil(false)) and
                      summary_processed_at > visit.processing_started_at)
             )
    end

(ie. it's just the not of the previous one) Is there a way to extract out the expression so I can do something like: filter expr(processed) and filter expr(not processed) I don't think I can use a calculation because it's using visit which is a relationship

8 Replies

ZachDaniel•2y ago

you can add an aggregate, and then use that in the calculation

aggregates do
  first :visit_processing_started_at, :visit, :processing_started_at
end

calculations do
  calculate :processed, expr(not is_nil(visit_processing_started_at) and ...)
end

aggregates do
  first :visit_processing_started_at, :visit, :processing_started_at
end

calculations do
  calculate :processed, expr(not is_nil(visit_processing_started_at) and ...)
end

rohanOP•2y ago

ohh that's clever haha

ZachDaniel•2y ago

another note: summary_processed_at(is_nil(false)) is probably not what you want i.e not is_nil(summary_processed_at)

rohanOP•2y ago

sorry little confused - is there a difference between those two or just aesthetically the latter is preferred i was a little confused by the is_nil stuff bc in the docs it said it's used like: x is_nil true

ZachDaniel•2y ago

hmm....gimme a sec 🙂 I believe that is incorrect you can use it when using the data structure version of filters, i.e x: [is_nil: true] huh looks like that does work I think I need to undo that because then you cant call functions w/ the result of is_nil(true) yeah, okay thats a bug 🙂 I'm fixing it now. It might break people's apps but there isn't really a way around it

rohanOP•2y ago

haha ok

\ ឵឵឵•2y ago

If I'm right in thinking that the limitation on using attributes of related resources in calculations is primarily about the potential for there to be multiple related resources, could this be supported for has_one and belongs_to relationships?

ZachDaniel•2y ago

yes, eventually 🙂 I think there is an issue for that actually

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