Ash Elixir•3y ago

Nested aggregates

In my Product Data Management webapp I'm trying to build with Ash, I have the following resources with attributes and relatioships in App.Api that, combined, construct/define an Item. * Category: has a :code attribute * Family: belongs_to a Category (and also has a :name, etc.) * Variant: belongs_to a Variant, has a :code attribute The idea is that an Item belongs_to a Category and a Variant, and has a calculated attribute (also called :code) resulting from concatenating the Category :code and the Variant :code. This means that Item's :code calculation must "pull" Category's :code through the Variant it belongs to, which belongs to a Family, which belongs to a Category. Item's calculated :code uniquely identifies a record. I have tried the following in a cascade, In lib/app/resources/item.ex:

  aggregates do
    first :category_code, :variant, :category_code
  end

  aggregates do
    first :category_code, :variant, :category_code
  end

In lib/app/resources/variant.ex:

  aggregates do
    first :category_code, :family, :category_code
  end

  aggregates do
    first :category_code, :family, :category_code
  end

In lib/app/resources/family.ex:

  aggregates do
    first :category_code, :category, :code
  end

  aggregates do
    first :category_code, :category, :code
  end

...hoping that App.Api.Item |> App.Api.read! would return records on which I can App.Api.load!(:code). Instead:

** (CaseClauseError) no case clause matching: {:error, [%Ash.Error.Unknown.UnknownError{error: "Must provide field type for first", field: nil, changeset: nil, query: nil, error_context: ["Loading aggregate: :category_code for query: #Ash.Query<resource: App.Api.Variant>"], vars: [], path: [:aggregates], stacktrace: #Stacktrace<>, class: :unknown}]}

** (CaseClauseError) no case clause matching: {:error, [%Ash.Error.Unknown.UnknownError{error: "Must provide field type for first", field: nil, changeset: nil, query: nil, error_context: ["Loading aggregate: :category_code for query: #Ash.Query<resource: App.Api.Variant>"], vars: [], path: [:aggregates], stacktrace: #Stacktrace<>, class: :unknown}]}

What is the Ash-idiomatic way of achieving the goal of being able to access Item's :code?

24 Replies

ZachDaniel•3y ago

You can’t currently reference aggregates from other aggregates However aggregates accept a relationship path. So you can say first [:foo, :bar, :baz], :code I need to give that a better error for sure.

waseigoOP•3y ago

first [:variant, :family, :category], :code ? it's getting marked as an error in VSCode (first/2 is not defined

ZachDaniel•3y ago

Ah, sorry My example was bad The first argument is the name So it’s name, path, field

waseigoOP•3y ago

Awesome! I also just realized that eval automatically casts the arguments to strings?

  aggregates do
    first :variant_code, :variant, :code
    first :category_code, [:variant, :family, :category], :code
  end

  calculations do
    calculate :code, :string, expr(category_code <> variant_code)
  end

  aggregates do
    first :variant_code, :variant, :code
    first :category_code, [:variant, :family, :category], :code
  end

  calculations do
    calculate :code, :string, expr(category_code <> variant_code)
  end

Both aggregates refer to :integer types in the other resources, but the result of the :code calculation is a :string

ZachDaniel•3y ago

Yeah, because the :<> operator is typed 🙂

waseigoOP•3y ago

nice! Thank you, wow are there lots of things I'm learning, thank you for all the help!

ZachDaniel•3y ago

Glad to be of assistance!

waseigoOP•3y ago

Though, now this works:

  preparations do
     prepare build(load: [:series_prefix, :category_code, :variant_code])
  end

  preparations do
     prepare build(load: [:series_prefix, :category_code, :variant_code])
  end

but this doesn't:

  preparations do
     prepare build(load: [:series_prefix, :category_code, :variant_code, :code])
  end

  preparations do
     prepare build(load: [:series_prefix, :category_code, :variant_code, :code])
  end

I'm getting ** (Postgrex.Error) ERROR 42883 (undefined_function) operator does not exist: bigint || bigint.

ZachDaniel•3y ago

🥲 I think you may need the type casts then

waseigoOP•3y ago

(I learned about preparations from another #support post)

ZachDaniel•3y ago

That is likely a bug in ash_postgres

waseigoOP•3y ago

as a workaround? how?

ZachDaniel•3y ago

Wrapping the things you’re concatenating with type(thing, :string)

waseigoOP•3y ago

wait, in the calculations or in the preparations block?

ZachDaniel•3y ago

In the calculation Like the typed operator thing I mentioned must not be doing the right thing for ash_postgres

waseigoOP•3y ago

    calculate :code, :string, expr(type(series_prefix, :string) <> type(category_code, :integer) <> type(variant_code, :integer))

    calculate :code, :string, expr(type(series_prefix, :string) <> type(category_code, :integer) <> type(variant_code, :integer))

same error

ZachDaniel•3y ago

The codes have to be cast to strings also

waseigoOP•3y ago

let me check, can I :load it or is it a preparations issue?

ZachDaniel•3y ago

Ash doesn’t always go to the database to load things

waseigoOP•3y ago

in the aggregates first definitions?

ZachDaniel•3y ago

So loading it after the fact might work In the example you showed change integer to string

waseigoOP•3y ago

yep, it works now! also, loading :code after the fact works when I didn't add it to the prepare statement this is one of the most important things I learned

ZachDaniel•3y ago

Yeah because Ash will sometimes choose to figure out calculations without going to the database. And so the elixir evaluation of that must work But the postgres one doesn’t Can you log a bug in ash_postgres?

waseigoOP•3y ago

Sure thing, here you go! https://github.com/ash-project/ash_postgres/issues/130

GitHub

Preparation does not work on a calculation, except when its paramet...

Describe the bug Preparation does not work on a calculation, except when its parameters are cast as strings. To Reproduce The following is a part of resource App.Api.Item. A Variant has_one Item, a...

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Nested aggregates

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