AE
Ash Elixir•2y ago
morfertaw

Attributes on `many_to_many` join/through resources.

Considering the following resources. 
defmodule Formula do
  use Ash.Resource,
    data_layer: Ash.DataLayer.Ets
  
  attributes do
    uuid_primary_key :id

    create_timestamp :created_at
    update_timestamp :updated_at
  end

  actions do
    defaults([:create, :read, :update, :destroy])

    create :define do

      argument :formula, {:array, :map}

      change manage_relationship(:formula, :reactants,
               on_lookup: :relate,
               on_no_match: :create,
               on_match: :update,
               on_missing: :unrelate
             )
    end

  end

  relationships do
    many_to_many :reactants, Reactant do
      through FormulaReactant
      source_attribute_on_join_resource :formula_id
      destination_attribute_on_join_resource :reactant_id
    end
  end

end
defmodule FormulaReactant do
  use Ash.Resource,
    data_layer: Ash.DataLayer.Ets
  attributes do
    attribute :quantity, :decimal do
      allow_nil? false
      constraints [min: 0.0]
    end

    attribute :unit, :string do
      allow_nil? false
      constraints trim?: true, allow_empty?: false, min_length: 1
    end
  end

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

  end

  relationships do
    belongs_to :formula, Formula, primary_key?: true, allow_nil?: false
    belongs_to :reactant, Reactant, primary_key?: true, allow_nil?: false
  end

end
defmodule Reactant do
  use Ash.Resource,
    data_layer: Ash.DataLayer.Ets
  
  attributes do
    uuid_primary_key :id

    attribute :name, :string

    create_timestamp :created_at
    update_timestamp :updated_at
  end

  actions do
    defaults([:create, :read, :update, :destroy])
  end
end
defmodule Formula do
  use Ash.Resource,
    data_layer: Ash.DataLayer.Ets
  
  attributes do
    uuid_primary_key :id

    create_timestamp :created_at
    update_timestamp :updated_at
  end

  actions do
    defaults([:create, :read, :update, :destroy])

    create :define do

      argument :formula, {:array, :map}

      change manage_relationship(:formula, :reactants,
               on_lookup: :relate,
               on_no_match: :create,
               on_match: :update,
               on_missing: :unrelate
             )
    end

  end

  relationships do
    many_to_many :reactants, Reactant do
      through FormulaReactant
      source_attribute_on_join_resource :formula_id
      destination_attribute_on_join_resource :reactant_id
    end
  end

end
defmodule FormulaReactant do
  use Ash.Resource,
    data_layer: Ash.DataLayer.Ets
  attributes do
    attribute :quantity, :decimal do
      allow_nil? false
      constraints [min: 0.0]
    end

    attribute :unit, :string do
      allow_nil? false
      constraints trim?: true, allow_empty?: false, min_length: 1
    end
  end

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

  end

  relationships do
    belongs_to :formula, Formula, primary_key?: true, allow_nil?: false
    belongs_to :reactant, Reactant, primary_key?: true, allow_nil?: false
  end

end
defmodule Reactant do
  use Ash.Resource,
    data_layer: Ash.DataLayer.Ets
  
  attributes do
    uuid_primary_key :id

    attribute :name, :string

    create_timestamp :created_at
    update_timestamp :updated_at
  end

  actions do
    defaults([:create, :read, :update, :destroy])
  end
end
The following create attempt fails. 
Formula
|>Ash.Changeset.for_create(:define, %{formula: [%{name: "pinata"}]})
|>Api.create()
Formula
|>Ash.Changeset.for_create(:define, %{formula: [%{name: "pinata"}]})
|>Api.create()
This is because attributes :quantity and :unit are not being set on FormulaReactant. How would a create action on Formula be setup to set both attributes?
3 Replies
barnabasj
barnabasj•2y ago
I don't think that there is anything out of the box that helps with this case, but the many_to_many also adds another relationship to your resource for the through resource https://ash-hq.org/docs/dsl/ash-resource#relationships-many_to_many-join_relationship So I think what you could do is something like this. 
defmodule Formula do

  ...

  actions do
    defaults([:create, :read, :update, :destroy])

    create :define do

      argument :formula, {:array, :map}

      change manage_relationship(:formula, :reactants_join_assoc,
               on_lookup: :relate,
               on_no_match: :create,
               on_match: :update,
               on_missing: :unrelate
             )
    end
  end
end

defmodule FormulaReactant do

  ...

  actions do
    defaults [:read, :destroy]

    create :create do
      argument :formula, :map
      
       pimary? true
      
      change manage_relationship(:reactant, :reactant,
        on_lookup: :relate,
        on_no_match: :create,
        on_match: :update,
        on_missing: :unrelate
      )
    end

    create :update do
      argument :formula, :map
      
       pimary? true
      
      change manage_relationship(:reactant, :reactant,
        on_lookup: :relate,
        on_no_match: :create,
        on_match: :update,
        on_missing: :unrelate
      )
    end
  end
end
defmodule Formula do

  ...

  actions do
    defaults([:create, :read, :update, :destroy])

    create :define do

      argument :formula, {:array, :map}

      change manage_relationship(:formula, :reactants_join_assoc,
               on_lookup: :relate,
               on_no_match: :create,
               on_match: :update,
               on_missing: :unrelate
             )
    end
  end
end

defmodule FormulaReactant do

  ...

  actions do
    defaults [:read, :destroy]

    create :create do
      argument :formula, :map
      
       pimary? true
      
      change manage_relationship(:reactant, :reactant,
        on_lookup: :relate,
        on_no_match: :create,
        on_match: :update,
        on_missing: :unrelate
      )
    end

    create :update do
      argument :formula, :map
      
       pimary? true
      
      change manage_relationship(:reactant, :reactant,
        on_lookup: :relate,
        on_no_match: :create,
        on_match: :update,
        on_missing: :unrelate
      )
    end
  end
end
Formula
|>Ash.Changeset.for_create(:define, %{formula: [%{quanity: 1, unit: "kg", reactant: %{name: "pinata"}}]})
|>Api.create()
Formula
|>Ash.Changeset.for_create(:define, %{formula: [%{quanity: 1, unit: "kg", reactant: %{name: "pinata"}}]})
|>Api.create()
In a way passing the data through the related resources yourself
morfertaw
morfertawOP•2y ago
Yeah, this is exactly what I was hoping for. Cheers!
barnabasj
barnabasj•2y ago
Btw, you don't need to make the actions the primary actions, you can also specify a specific action per operation e.g on_no_match: {:create, :create_action_name}

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