85 replies

Serialized access to instance of resource for `AshPostgres`

Pursuant to the discussion in #general , I'd like to create a macro which uses the

changes

changes

hook to ensure that change actions to an instance (row) of a resource are serialized. For now I'm only looking at Postgres support, but if the

lock

lock

primitive comes into play, happy to update. Primary changes are the addition of a definitely-not-working locking statement and

or changeset.type == :read

or changeset.type == :read

to not block

read

read

actions.

defmodule AshPostgresUtil.SerializedChanges do
  defmacro __using__(opts \\ []) do
    changes do
      change fn changeset, _ ->
        unless changeset.context[:locked][changeset.data.id] or changeset.type == :read do
          Ash.Changeset.before_action(changeset, fn changeset ->
            Ash.set_context(%{locked: %{changeset.data.id => true}})

            # something like this
            unquote(__CALLER__.module)
            |> lock("FOR UPDATE")
            |> unquote(opts[:repo]).get!(changeset.data.id)

            changeset
          end)
          |> Ash.Changeset.after_action(fn changeset, result ->
            Ash.set_context(%{locked: %{changeset.data.id => false}})
            {:ok, result}
          end)
        else
          changeset
        end
      end
    end
  end
end

defmodule AshPostgresUtil.SerializedChanges do
  defmacro __using__(opts \\ []) do
    changes do
      change fn changeset, _ ->
        unless changeset.context[:locked][changeset.data.id] or changeset.type == :read do
          Ash.Changeset.before_action(changeset, fn changeset ->
            Ash.set_context(%{locked: %{changeset.data.id => true}})

            # something like this
            unquote(__CALLER__.module)
            |> lock("FOR UPDATE")
            |> unquote(opts[:repo]).get!(changeset.data.id)

            changeset
          end)
          |> Ash.Changeset.after_action(fn changeset, result ->
            Ash.set_context(%{locked: %{changeset.data.id => false}})
            {:ok, result}
          end)
        else
          changeset
        end
      end
    end
  end
end

Usage:

defmodule Bookstore.EnrollmentFlow do
  use Ash.Resource, data_layer: AshPostgres.DataLayer
  use AshPostgresUtil.SerializedChanges, repo: Bookstore.Repo

  # ...
end

defmodule Bookstore.EnrollmentFlow do
  use Ash.Resource, data_layer: AshPostgres.DataLayer
  use AshPostgresUtil.SerializedChanges, repo: Bookstore.Repo

  # ...
end

Two things:
- This relies on the changeset and its children happening inside a transaction. Is that the case?
- I'm using the resource as if it's an Ecto schema. This is...maybe not legit. The Ash changeset (or parts of it) will end up as an Ecto changeset at some point, though. Is there an escape hatch I can use here to inject this or raw SQL into the changeset?

Ash Framework•3y ago•

85 replies

\ ឵឵឵

Serialized access to instance of resource for `AshPostgres`

Pursuant to the discussion in #general , I'd like to create a macro which uses the

changes

changes

hook to ensure that change actions to an instance (row) of a resource are serialized. For now I'm only looking at Postgres support, but if the

lock

lock

primitive comes into play, happy to update. Primary changes are the addition of a definitely-not-working locking statement and

or changeset.type == :read

or changeset.type == :read

to not block

read

read

actions.

defmodule AshPostgresUtil.SerializedChanges do
  defmacro __using__(opts \\ []) do
    changes do
      change fn changeset, _ ->
        unless changeset.context[:locked][changeset.data.id] or changeset.type == :read do
          Ash.Changeset.before_action(changeset, fn changeset ->
            Ash.set_context(%{locked: %{changeset.data.id => true}})

            # something like this
            unquote(__CALLER__.module)
            |> lock("FOR UPDATE")
            |> unquote(opts[:repo]).get!(changeset.data.id)

            changeset
          end)
          |> Ash.Changeset.after_action(fn changeset, result ->
            Ash.set_context(%{locked: %{changeset.data.id => false}})
            {:ok, result}
          end)
        else
          changeset
        end
      end
    end
  end
end

defmodule AshPostgresUtil.SerializedChanges do
  defmacro __using__(opts \\ []) do
    changes do
      change fn changeset, _ ->
        unless changeset.context[:locked][changeset.data.id] or changeset.type == :read do
          Ash.Changeset.before_action(changeset, fn changeset ->
            Ash.set_context(%{locked: %{changeset.data.id => true}})

            # something like this
            unquote(__CALLER__.module)
            |> lock("FOR UPDATE")
            |> unquote(opts[:repo]).get!(changeset.data.id)

            changeset
          end)
          |> Ash.Changeset.after_action(fn changeset, result ->
            Ash.set_context(%{locked: %{changeset.data.id => false}})
            {:ok, result}
          end)
        else
          changeset
        end
      end
    end
  end
end

Usage:

defmodule Bookstore.EnrollmentFlow do
  use Ash.Resource, data_layer: AshPostgres.DataLayer
  use AshPostgresUtil.SerializedChanges, repo: Bookstore.Repo

  # ...
end

defmodule Bookstore.EnrollmentFlow do
  use Ash.Resource, data_layer: AshPostgres.DataLayer
  use AshPostgresUtil.SerializedChanges, repo: Bookstore.Repo

  # ...
end

Serialized access to instance of resource for `AshPostgres`

Serialized access to instance of resource for `AshPostgres`

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