AE
Ash Elixir•3w ago
adonig

Framework Error - Assumption failed: Invalid return from calculation

Hi, I’m encountering a Framework Error with the message:
Assumption failed: Invalid return from calculation, expected a value, got %Ash.NotLoaded{}
The full error trace is attached below. I'm unsure whether this is caused by a mistake on my side or if it's a potential bug in the framework. If you need any additional details (resource definitions, calculations, test cases, etc.), I’m happy to provide them. Thanks in advance!

message.txt

9 Replies
barnabasj
barnabasj•3w ago
A reproduction would be great
adonig
adonigOP•3w ago
It's a bit messy. I see what I can do to make it minimal 😅
adonig
adonigOP•3w ago
This test reproduces the error. It's still a lot of stuff going on. Let me know when you have any questions.

repro_test.ex

barnabasj
barnabasj•3w ago
You were missing load statements in your changes 
  defmodule BuildingTypeCalculation do
    use Ash.Resource.Calculation
    
    @impl true
    def load(_query, _opts, _context), do: :_building_type # <= this was missing 

    @impl true
    def calculate(generals, _opts, _context) do
      Enum.map(dbg(generals), fn general ->
        case Map.get(general, :_building_type) do
          nil -> guess_building_type(general)
          building_type -> building_type # <= This was passing through the %Ash.NotLoaded{} struct
        end
      end)
    end

    defp guess_building_type(_general) do
      :single_family
    end
  end
  defmodule BuildingTypeCalculation do
    use Ash.Resource.Calculation
    
    @impl true
    def load(_query, _opts, _context), do: :_building_type # <= this was missing 

    @impl true
    def calculate(generals, _opts, _context) do
      Enum.map(dbg(generals), fn general ->
        case Map.get(general, :_building_type) do
          nil -> guess_building_type(general)
          building_type -> building_type # <= This was passing through the %Ash.NotLoaded{} struct
        end
      end)
    end

    defp guess_building_type(_general) do
      :single_family
    end
  end
  defmodule SpecificSpaceHeatingDemandCalculation do
    use Ash.Resource.Calculation

    @impl true
    def calculate(heatings, _opts, _context),
      do: Enum.map(heatings, fn heating -> guess_specific_space_heating_demand(heating) end)

    @impl true
    def load(_query, _opts, _context) do
      # load only selects the given fields on the related resource
      # that's why _building_type and the other fields weren't loaded in
      # the nested calculations
      [household: [general: [:construction_year]]] # <= 
    end

    def guess_specific_space_heating_demand(heating) do
      construction_year = heating.household.general.construction_year

      if is_nil(construction_year) do
        raise(
          ArgumentError,
          "Cannot estimate specific space heating demand without construction year"
        )
      end

      case construction_year do
        year when year <= 1949 -> 300
        year when year <= 1978 -> 200
        year when year <= 1995 -> 150
        year when year <= 2001 -> 100
        year when year <= 2009 -> 75
        year when year <= 2015 -> 50
        _year -> 40
      end
    end
  end
  defmodule SpecificSpaceHeatingDemandCalculation do
    use Ash.Resource.Calculation

    @impl true
    def calculate(heatings, _opts, _context),
      do: Enum.map(heatings, fn heating -> guess_specific_space_heating_demand(heating) end)

    @impl true
    def load(_query, _opts, _context) do
      # load only selects the given fields on the related resource
      # that's why _building_type and the other fields weren't loaded in
      # the nested calculations
      [household: [general: [:construction_year]]] # <= 
    end

    def guess_specific_space_heating_demand(heating) do
      construction_year = heating.household.general.construction_year

      if is_nil(construction_year) do
        raise(
          ArgumentError,
          "Cannot estimate specific space heating demand without construction year"
        )
      end

      case construction_year do
        year when year <= 1949 -> 300
        year when year <= 1978 -> 200
        year when year <= 1995 -> 150
        year when year <= 2001 -> 100
        year when year <= 2009 -> 75
        year when year <= 2015 -> 50
        _year -> 40
      end
    end
  end
the load callback is for also for attributes, because they can als be %Ash.NotLoaded{} when they are not selected, so you need to make sure to have them in calc load statements as well. Not just other calculations and relationships and so on
adonig
adonigOP•3w ago
so it's not recursively resolving the dependencies of the loaded calculations?
barnabasj
barnabasj•3w ago
It does, but the nested calculations didn't have the necessary fields in the loads. _building_type was not specified in any of the calculations
adonig
adonigOP•3w ago
Oh now I get it, so the calculations even have to explicitly load the fields on the resource they are attached to, not only the fields from relations. I added all of them and now it works! Thank you very much for the help! 🙇‍♂️
barnabasj
barnabasj•3w ago
yeah, exactly. This might have been more explicit in Ash 2.0 https://hexdocs.pm/ash/upgrading-to-3-0.html#calculations-do-not-have-a-select-3-callback-any-more It's mentioned here in the comment for the load statement https://hexdocs.pm/ash/calculations.html#module-calculations but we could probably make it a bit more visible
adonig
adonigOP•3w ago
I read through that code comment but because it only mentions: posts: [:title, :body]. I thought it applies only to loading relationship fields. But now that I think about it again, it makes much more sense that you have to explicitly load everything in a calculation, even fields on the same resource.

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