Ash Elixir•3y ago

Conditional filters in read actions

Hi there, I'm back with another quesion that i couldnt find an answer to - sorry if i missed something. I have a resource with a list of form submissions, where i have a read action to get all form submission of a specific form id, with the form_id as an argument. that works fine. Now i also want to add the possibility to get all records submitted after a specific date, which also works this way: filter expr(submission_time >= ^arg(:min_submission_time)). Now, the :min_submission_time argument is optional - i want to be able to use the same action for getting both all as well as the filtered submissions. Is there a way to have a conditional in the action to only apply the :min_submission_time filter if the argument is not nil? As far as I know the action code is evaluated at compile time, so i cant use a normal elixir if/else. I am aware that i could just split this up into 2 different actions, but that would require duplicating things like the default sort order and filtering by form id. Thanks!

6 Replies

ZachDaniel•3y ago

You have to options 🙂 the built in filter option is really just short hand for adding a custom preparation that filters.

prepare fn query, _ ->
  if query.arguments[:submission_time] do
    Ash.Query.filter(…)
  else
    query 
  end
end

prepare fn query, _ ->
  if query.arguments[:submission_time] do
    Ash.Query.filter(…)
  else
    query 
  end
end

The other option is that ash expressions support if

expr(
  if ^arg(:min_submission_tjme) do
    submission_time >= ^arg(:min_submission_time)
  else
    true
  end
)

expr(
  if ^arg(:min_submission_tjme) do
    submission_time >= ^arg(:min_submission_time)
  else
    true
  end
)

fekleOP•3y ago

Thanks! I tried the second solution but found the following - if I keep the else true in it, then it seems to ignore other filters in the action - if i remove the else true then i always get 0 results thats how it looks now:

read :get_records do
      argument :form_id, :integer do
        allow_nil? false
      end

      argument :min_submission_time, :utc_datetime do
        allow_nil? true
      end

      prepare build(sort: [submission_id: :desc])

      filter expr(form_id == ^arg(:form_id))

      filter expr(
               if not is_nil(^arg(:min_submission_time)) do
                 submission_time >= ^arg(:min_submission_time)
               else
                 true
               end
             )
    end

read :get_records do
      argument :form_id, :integer do
        allow_nil? false
      end

      argument :min_submission_time, :utc_datetime do
        allow_nil? true
      end

      prepare build(sort: [submission_id: :desc])

      filter expr(form_id == ^arg(:form_id))

      filter expr(
               if not is_nil(^arg(:min_submission_time)) do
                 submission_time >= ^arg(:min_submission_time)
               else
                 true
               end
             )
    end

OK, my bad it always ignores the first filter - seems like i can only have one filter. I can combine both filters like this - is that the "idiomatic" syntax for this?

     filter [
        expr(form_id == ^arg(:form_id)),
        expr(
          if not is_nil(^arg(:min_submission_time)) do
            submission_time >= ^arg(:min_submission_time)
          else
            true
          end
        )
      ]

     filter [
        expr(form_id == ^arg(:form_id)),
        expr(
          if not is_nil(^arg(:min_submission_time)) do
            submission_time >= ^arg(:min_submission_time)
          else
            true
          end
        )
      ]

ZachDaniel•3y ago

Nope, that won’t work. That would always return everything. You’d combine them into a single expression with or Or and But yeah there can currently only be one filter. Many people have asked for there to be multiple so I should probably just do that today 🙂

fekleOP•3y ago

Well but when i think of it, if there are multiple filters then its unclear if they are AND or OR 🙂 so there would need to be a new syntax so you mean like this?

filter expr(
               expr(form_id == ^arg(:form_id)) and
                 expr(
                   if not is_nil(^arg(:min_submission_time)) do
                     submission_time >= ^arg(:min_submission_time)
                   else
                     true
                   end
                 )
             )

filter expr(
               expr(form_id == ^arg(:form_id)) and
                 expr(
                   if not is_nil(^arg(:min_submission_time)) do
                     submission_time >= ^arg(:min_submission_time)
                   else
                     true
                   end
                 )
             )

cleaner like this, seems to work - thanks!! 🙂

 filter expr(
               form_id == ^arg(:form_id) and
                 if not is_nil(^arg(:min_submission_time)) do
                   submission_time >= ^arg(:min_submission_time)
                 else
                   true
                 end
             )

 filter expr(
               form_id == ^arg(:form_id) and
                 if not is_nil(^arg(:min_submission_time)) do
                   submission_time >= ^arg(:min_submission_time)
                 else
                   true
                 end
             )

ZachDaniel•3y ago

filter expr(...)
filter expr(...)

filter expr(...)
filter expr(...)

when I support that, it will be and similarly to how calling query |> Ash.Query.filter(...) |> Ash.Query.filter(...) will use and but Yeah that looks great 🙂

fekleOP•3y ago

great, thanks again for your help!

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Conditional filters in read actions

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