Create a resource including a belongs_to id

I have this resource with the name location:

attributes do
  uuid_primary_key :id

  attribute :name
  attribute :code, :string
  attribute :slug, :string
end

relationships do
  belongs_to :level, Feriendaten.Geo.Level
end

attributes do
  uuid_primary_key :id

  attribute :name
  attribute :code, :string
  attribute :slug, :string
end

relationships do
  belongs_to :level, Feriendaten.Geo.Level
end

Now I want to create a new entry for this resource with this code:

 level =
    Feriendaten.Geo.Level
    |> Ash.Query.filter(contains(slug, "land"))
    |> Feriendaten.Geo.read!()
    |> hd()

  Feriendaten.Geo.Location
  |> Ash.Changeset.for_create(:create, %{
    name: "Germany",
    code: "DE",
    slug: "germany",
    level_id: level.id
  })
  |> Feriendaten.Geo.create!()

 level =
    Feriendaten.Geo.Level
    |> Ash.Query.filter(contains(slug, "land"))
    |> Feriendaten.Geo.read!()
    |> hd()

  Feriendaten.Geo.Location
  |> Ash.Changeset.for_create(:create, %{
    name: "Germany",
    code: "DE",
    slug: "germany",
    level_id: level.id
  })
  |> Feriendaten.Geo.create!()

The recourse Location gets created but the attribute level_id is empty. How can I achieve to create a Location with the belongs_to association?

6 Replies

Rebecca Le•3y ago

in your create action definition, you would use manage_relationship to allow the setting of the level_id - let me grab an example In your Location resource:

actions do
  create :create do
    primary? true
    change manage_relationship(:level_id, :level, type: :append_and_remove)
    ...

actions do
  create :create do
    primary? true
    change manage_relationship(:level_id, :level, type: :append_and_remove)
    ...

this would allow the level_id attribute to be set when creating a Location, ensuring it's also a valid value etc.

Stefan WintermeyerOP•3y ago

Thanks @Rebecca Le ! For the archive. The function needs an addition line:

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

  create(:create) do
    argument :level_id, :string
    primary? true
    change manage_relationship(:level_id, :level, type: :append_and_remove)
  end
end

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

  create(:create) do
    argument :level_id, :string
    primary? true
    change manage_relationship(:level_id, :level, type: :append_and_remove)
  end
end

Withouth the argument :level_id, :string it doesn't work.

ZachDaniel•3y ago

You can also set attribute_writable? true on the relationship to make the attribute that it adds writable as a normal attribute.

Stefan WintermeyerOP•3y ago

Much cleaner. Thank you Zach!

ZachDaniel•3y ago

There are some differences in their behavior, for instance if you have policies on reading the related resource, manage_relationship will look it up first to make sure you can read it, that kind of thing. but attribute_writable? is simpler generally, yes. manage_relationship would be required for every other type of relationship though since they don't have an associated attribute like belongs_to does.

sevenseacat•3y ago

TIL also, thanks 😄

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Create a resource including a belongs_to id

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