Ash Framework•3mo ago

Optional argument with defaults for actions

It feels like it should be something really simple but its just not working out. I have a resource with a non-null string attribute that defaults to an empty string

  attributes do
    uuid_primary_key :id

    attribute :title, :string do
      allow_nil? false
      default ""
      description "Row title for display purposes"
    end
  ...
  end

  attributes do
    uuid_primary_key :id

    attribute :title, :string do
      allow_nil? false
      default ""
      description "Row title for display purposes"
    end
  ...
  end

Then how can I get the action to accept an optional argument for title, defaulting to an empty string? Something like this:

    create :create do
      accept [:title, :data, :table_id, :position]

    create :create do
      accept [:title, :data, :table_id, :position]

Will raise an error telling me title is required. And something like this

    create :create do
      argument :title, :string, allow_nil?: true, default: ""
      accept [:data, :table_id, :position]
    
      change set_attribute(:title, arg(:title))
      # or even this 
      # change set_attribute(:title, "")

    create :create do
      argument :title, :string, allow_nil?: true, default: ""
      accept [:data, :table_id, :position]
    
      change set_attribute(:title, arg(:title))
      # or even this 
      # change set_attribute(:title, "")

somehow still raises with the same changeset error. I feel like I'm missing something really obvious 😓

Solution:

You can also constraints: [allow_empty?: true]

Jump to solution

5 Replies

HorizonOP•3mo ago

turns out empty string as argument will evalulate to nil. i.e.

      argument :title, :string, allow_nil?: true, default: "a"
      change set_attribute(:title, arg(:title))

      argument :title, :string, allow_nil?: true, default: "a"
      change set_attribute(:title, arg(:title))

This will work and correctly set title attribute to "a"

      argument :title, :string, allow_nil?: true, default: ""
      change set_attribute(:title, arg(:title))

      argument :title, :string, allow_nil?: true, default: ""
      change set_attribute(:title, arg(:title))

here title attribute will remain as nil I suspect this is here to help translating empty form values to nil .

Chaz Watkins•3mo ago

Hey James - You're likely looking for allow_nil_input on the create action. https://hexdocs.pm/ash/dsl-ash-resource.html#actions-create-allow_nil_input This allows you to have an attribute be allow_nil? false, but make it optional

Solution

ZachDaniel•3mo ago

You can also constraints: [allow_empty?: true]

ZachDaniel•3mo ago

i.e attribute :title, :string, constraints: [allow_empty?: true, trim?: false] skips the standard sanitization we do to trim whitespace around the value and then turn "" -> nil

HorizonOP•3mo ago

I was just about the say that even with allow_nil_input? the action will fail due to sanitization but the constraint to skip sanitization works like a charm. Thank you Chaz and Zach! 😄

Gaming

Programming

Optional argument with defaults for actions

Did you find this page helpful?