Ash Framework•2mo ago

Adding new changeset arguments in `before_action`

Hi, I'm having a bit of trouble understanding the order in which changes get executed within an update action and how to set arguments. Suppose I have something like:

update :foo do
  require_atomic? false
  
  accept []

  argument :arg1, :string, allow_nil?: false

  change before_action(fn changeset, _context ->
    record = changeset.data

    nested_resource = NestedResource.create!(%{parent_id: record.id})

    Ash.Changeset.set_argument(changeset, :nested_resource_id, nested_resource.id)
  end)

  change fn changeset, _context ->
    dbg(changeset.arguments)

    changeset
  end
end

update :foo do
  require_atomic? false
  
  accept []

  argument :arg1, :string, allow_nil?: false

  change before_action(fn changeset, _context ->
    record = changeset.data

    nested_resource = NestedResource.create!(%{parent_id: record.id})

    Ash.Changeset.set_argument(changeset, :nested_resource_id, nested_resource.id)
  end)

  change fn changeset, _context ->
    dbg(changeset.arguments)

    changeset
  end
end

Running :foo on a resource prints the following in the IEx:

arguments #=> %{
  nil: "0198908a-c4ca-7c4f-831e-b67ea589f4c8",
  arg1: "description"
}

arguments #=> %{
  nil: "0198908a-c4ca-7c4f-831e-b67ea589f4c8",
  arg1: "description"
}

where the value associated with nil is the nested_resource.id. I have two questions: 1. At what point do changes that are not before_action, etc get run? 2. Is this a bug that an argument gets a key of nil instead of :nested_resource_id?

8 Replies

ZachDaniel•2mo ago

https://hexdocs.pm/ash/actions.html#complete-lifecycle-flow THe changes run first and then any before actions that were added run after that

Igor BarakaievOP•2mo ago

How is it that in the example above the arguments get populated with :nested_resource_id's value under nil key? 🤔

ZachDaniel•2mo ago

🤔 I have no idea actually Does that not happen if you remove the before_action change above it? THat seems unrelated to me TBH

Igor BarakaievOP•2mo ago

if instead of just doing set_argument I do something hacky like Map.put(changeset, :arguments, Map.put(changeset.arguments, :nested_resource_id, nested_resource.id)), then the debug actually prints:

arguments #=> %{
  nested_resource_id: "0198908a-c4ca-7c4f-831e-b67ea589f4c8",
  arg1: "description"
}

arguments #=> %{
  nested_resource_id: "0198908a-c4ca-7c4f-831e-b67ea589f4c8",
  arg1: "description"
}

ZachDaniel•2mo ago

oh wow its because there is no such argument with that name it must be a bug w/ how we handle that please open an issue you can't set_argument for args taht don't exit

Igor BarakaievOP•2mo ago

ah damn, I was kind of depending on running set_argument to add new arguments dynamically 🫣 (in my hacky way)

ZachDaniel•2mo ago

You can use set_context and read from context You can also have private arguments

Igor BarakaievOP•2mo ago

ah yes, that's the right approach. I'll open an issue about the nil thing

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Adding new changeset arguments in `before_action`

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