add_tag but unique

A product has a many_to_many relationship to a tag (via a product_tag resource).
lib/app/shop/resources/product.ex

    [...]
    create :create do
      primary? true
      argument :tags, {:array, :map}

      argument :add_tag, :map do
        allow_nil? false
      end

      change manage_relationship(:tags, type: :append_and_remove, on_no_match: :create)
      change manage_relationship(:add_tag, :tags, type: :create)
    end
    [...]

    [...]
    create :create do
      primary? true
      argument :tags, {:array, :map}

      argument :add_tag, :map do
        allow_nil? false
      end

      change manage_relationship(:tags, type: :append_and_remove, on_no_match: :create)
      change manage_relationship(:add_tag, :tags, type: :create)
    end
    [...]

This works nicely:

iex(6)> banana = App.Shop.Product.create!(%{name: "Banana", add_tag: %{name: "Yellow"}})

iex(6)> banana = App.Shop.Product.create!(%{name: "Banana", add_tag: %{name: "Yellow"}})

Unfortunately I can also add another "Yellow" tag via an update:

iex(7)> App.Shop.Product.update!(banana, %{add_tag: %{name: "Yellow"}}).tags |> Enum.map(& &1.name)
["Yellow", "Yellow"]

iex(7)> App.Shop.Product.update!(banana, %{add_tag: %{name: "Yellow"}}).tags |> Enum.map(& &1.name)
["Yellow", "Yellow"]

Obviously this should not happen. The "Yellow" tag should be unique. The longer I think about this the lesser I know how to solve it. Should I through a validation error? How can I do this? Should I just OK it but not adding another tag? How would I do that?

10 Replies

barnabasj•2y ago

You can add identities to your tag resource making the names unique, in that case the manage_relationsgip can use the name to lookup existing tags. You might need to add some options to the manage_relationship call, telling it which identities to use.

Stefan WintermeyerOP•2y ago

Can you give me an example of how to setup an identity? https://hexdocs.pm/ash/identities.html doesn't have any examples and the https://ash-hq.org internal search engine doesn't work right now. Here's my tag resource:

defmodule App.Shop.Tag do
  use Ash.Resource, data_layer: Ash.DataLayer.Ets

  attributes do
    uuid_primary_key :id
    attribute :name, :string
  end

  relationships do
    many_to_many :products, App.Shop.Product do
      through App.Shop.ProductTag
      source_attribute_on_join_resource :tag_id
      destination_attribute_on_join_resource :product_id
    end
  end

  actions do
    defaults [:read, :update, :destroy]

    create :create do
      primary? true
      argument :products, {:array, :map}
      change manage_relationship(:products, type: :append_and_remove, on_no_match: :create)
    end
  end

  code_interface do
    define_for App.Shop
    define :create
    define :read
    define :by_id, get_by: [:id], action: :read
    define :by_name, get_by: [:name], action: :read
    define :update
    define :destroy
  end
end

defmodule App.Shop.Tag do
  use Ash.Resource, data_layer: Ash.DataLayer.Ets

  attributes do
    uuid_primary_key :id
    attribute :name, :string
  end

  relationships do
    many_to_many :products, App.Shop.Product do
      through App.Shop.ProductTag
      source_attribute_on_join_resource :tag_id
      destination_attribute_on_join_resource :product_id
    end
  end

  actions do
    defaults [:read, :update, :destroy]

    create :create do
      primary? true
      argument :products, {:array, :map}
      change manage_relationship(:products, type: :append_and_remove, on_no_match: :create)
    end
  end

  code_interface do
    define_for App.Shop
    define :create
    define :read
    define :by_id, get_by: [:id], action: :read
    define :by_name, get_by: [:name], action: :read
    define :update
    define :destroy
  end
end

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barnabasj•2y ago

https://hexdocs.pm/ash/dsl-ash-resource.html#identities unfortunately I only have my phone right now, so it's a bit hard to write code

ZachDaniel•2y ago

yep, from that guide:

identities do
  identity :unique_name, [:name]
end

identities do
  identity :unique_name, [:name]
end

and then:

change manage_relationship(:products, type: :append_and_remove, on_no_match: :create, use_identities: [:unique_name])

change manage_relationship(:products, type: :append_and_remove, on_no_match: :create, use_identities: [:unique_name])

Stefan WintermeyerOP•2y ago

Do I use it wrong? Here's the tag resource:

defmodule App.Shop.Tag do
  use Ash.Resource, data_layer: Ash.DataLayer.Ets

  attributes do
    uuid_primary_key :id
    attribute :name, :string
  end

  identities do
    identity :unique_name, [:name]
  end

  relationships do
    many_to_many :products, App.Shop.Product do
      through App.Shop.ProductTag
      source_attribute_on_join_resource :tag_id
      destination_attribute_on_join_resource :product_id
    end
  end

  actions do
    defaults [:read, :update, :destroy]

    create :create do
      primary? true
      argument :products, {:array, :map}

      change manage_relationship(:products,
               type: :append_and_remove,
               on_no_match: :create,
               use_identities: [:unique_name]
             )
    end
  end

  code_interface do
    define_for App.Shop
    define :create
    define :read
    define :by_id, get_by: [:id], action: :read
    define :by_name, get_by: [:name], action: :read
    define :update
    define :destroy
  end
end

defmodule App.Shop.Tag do
  use Ash.Resource, data_layer: Ash.DataLayer.Ets

  attributes do
    uuid_primary_key :id
    attribute :name, :string
  end

  identities do
    identity :unique_name, [:name]
  end

  relationships do
    many_to_many :products, App.Shop.Product do
      through App.Shop.ProductTag
      source_attribute_on_join_resource :tag_id
      destination_attribute_on_join_resource :product_id
    end
  end

  actions do
    defaults [:read, :update, :destroy]

    create :create do
      primary? true
      argument :products, {:array, :map}

      change manage_relationship(:products,
               type: :append_and_remove,
               on_no_match: :create,
               use_identities: [:unique_name]
             )
    end
  end

  code_interface do
    define_for App.Shop
    define :create
    define :read
    define :by_id, get_by: [:id], action: :read
    define :by_name, get_by: [:name], action: :read
    define :update
    define :destroy
  end
end

With that I get this error:

** (EXIT from #PID<0.98.0>) an exception was raised:
    ** (Spark.Error.DslError) [App.Shop.Tag]
 The data layer does not support native checking of identities.

Identities: unique_name

Must specify the `pre_check_with` option.

        (spark 1.1.39) lib/spark/dsl/extension.ex:560: Spark.Dsl.Extension.raise_transformer_error/2
        (elixir 1.15.5) lib/enum.ex:4830: Enumerable.List.reduce/3
        (elixir 1.15.5) lib/enum.ex:2564: Enum.reduce_while/3
        (elixir 1.15.5) lib/enum.ex:984: Enum."-each/2-lists^foreach/1-0-"/2
        (elixir 1.15.5) lib/module/parallel_checker.ex:271: Module.ParallelChecker.check_module/3
        (elixir 1.15.5) lib/module/parallel_checker.ex:82: anonymous fn/6 in Module.ParallelChecker.spawn/4

** (EXIT from #PID<0.98.0>) an exception was raised:
    ** (Spark.Error.DslError) [App.Shop.Tag]
 The data layer does not support native checking of identities.

Identities: unique_name

Must specify the `pre_check_with` option.

        (spark 1.1.39) lib/spark/dsl/extension.ex:560: Spark.Dsl.Extension.raise_transformer_error/2
        (elixir 1.15.5) lib/enum.ex:4830: Enumerable.List.reduce/3
        (elixir 1.15.5) lib/enum.ex:2564: Enum.reduce_while/3
        (elixir 1.15.5) lib/enum.ex:984: Enum."-each/2-lists^foreach/1-0-"/2
        (elixir 1.15.5) lib/module/parallel_checker.ex:271: Module.ParallelChecker.check_module/3
        (elixir 1.15.5) lib/module/parallel_checker.ex:82: anonymous fn/6 in Module.ParallelChecker.spawn/4

barnabasj•2y ago

I have used identities only with the postgres layer before, looks like you need to configure the pre_check_with option and pass it the API that holds the resource

ZachDaniel•2y ago

Yes, Ash.DataLayer.Ets doesn't have unique enforcement in the data layer, so it has to do a check before inserting Ideally we would build that feature into the ETS data layer, but until then it requires that setting to be configured

Stefan WintermeyerOP•2y ago

How does that work code wise? https://ash-hq.org/docs/dsl/ash-resource#identities-identity-pre_check_with doesn't include an example.

ZachDaniel•2y ago

pre_check_with Your.Api in the identity definition

identity :name, [:field] do
  pre_check_with API
end

identity :name, [:field] do
  pre_check_with API
end

Stefan WintermeyerOP•2y ago

For the archive:

  identities do
    # identity :unique_name, [:name] <1>

    identity :name, [:name] do
      pre_check_with App.Shop
    end
  end

  identities do
    # identity :unique_name, [:name] <1>

    identity :name, [:name] do
      pre_check_with App.Shop
    end
  end

<1> Use with a PostgreSQL DB.

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add_tag but unique

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