fix: use data from result for properly atomic transfer verification

Author: zachdaniel

lib/transfer/changes/verify_transfer.ex

@@ -51,9 +51,9 @@ defmodule AshDoubleEntry.Transfer.Changes.VerifyTransfer do
         end
         |> maybe_destroy_balances(context)
         |> Ash.Changeset.after_action(fn changeset, result ->
-          from_account_id = Ash.Changeset.get_attribute(changeset, :from_account_id)
-          to_account_id = Ash.Changeset.get_attribute(changeset, :to_account_id)
-          new_amount = Ash.Changeset.get_attribute(changeset, :amount)
+          from_account_id = result.from_account_id
+          to_account_id = result.to_account_id
+          new_amount = result.amount
 
           old_amount =
             if changeset.action.type == :destroy do

test/ash_double_entry_test.exs

@@ -271,8 +271,11 @@ defmodule AshDoubleEntryTest do
         Ash.destroy!(transfer_2)
       end
 
+      # we test atomic destroy here
       assert_raise Ash.Error.Invalid, ~r/balance cannot be negative/, fn ->
-        Ash.destroy!(transfer_3)
+        Transfer
+        |> Ash.Query.filter(id == ^transfer_3.id)
+        |> Ash.bulk_destroy!(:destroy, %{}, return_errors?: true)
       end
 
       Ash.destroy!(transfer_4)

test/support/balance.ex

@@ -41,6 +41,10 @@ defmodule AshDoubleEntry.Test.Balance do
   postgres do
     table "balances"
     repo(AshDoubleEntry.Test.Repo)
+
+    references do
+      reference(:transfer, on_delete: :delete)
+    end
   end
 
   balance do

test/support/migrations/20250410173546_delete_balances.exs

@@ -0,0 +1,36 @@
+defmodule AshDoubleEntry.Test.Repo.Migrations.DeleteBalances do
+  @moduledoc """
+  Updates resources based on their most recent snapshots.
+
+  This file was autogenerated with `mix ash_postgres.generate_migrations`
+  """
+
+  use Ecto.Migration
+
+  def up do
+    drop(constraint(:balances, "balances_transfer_id_fkey"))
+
+    alter table(:balances) do
+      modify(
+        :transfer_id,
+        references(:transfers,
+          column: :id,
+          name: "balances_transfer_id_fkey",
+          type: :binary,
+          on_delete: :delete_all
+        )
+      )
+    end
+  end
+
+  def down do
+    drop(constraint(:balances, "balances_transfer_id_fkey"))
+
+    alter table(:balances) do
+      modify(
+        :transfer_id,
+        references(:transfers, column: :id, name: "balances_transfer_id_fkey", type: :binary)
+      )
+    end
+  end
+end

test/support/snapshots/repo/balances/20250410173546.json

@@ -0,0 +1,116 @@
+{
+  "attributes": [
+    {
+      "allow_nil?": false,
+      "default": "fragment(\"gen_random_uuid()\")",
+      "generated?": true,
+      "primary_key?": true,
+      "references": null,
+      "size": null,
+      "source": "id",
+      "type": "uuid"
+    },
+    {
+      "allow_nil?": false,
+      "default": "nil",
+      "generated?": false,
+      "primary_key?": false,
+      "references": null,
+      "size": null,
+      "source": "balance",
+      "type": "money_with_currency"
+    },
+    {
+      "allow_nil?": false,
+      "default": "nil",
+      "generated?": false,
+      "primary_key?": false,
+      "references": {
+        "deferrable": false,
+        "destination_attribute": "id",
+        "destination_attribute_default": null,
+        "destination_attribute_generated": null,
+        "index?": false,
+        "match_type": null,
+        "match_with": null,
+        "multitenancy": {
+          "attribute": null,
+          "global": null,
+          "strategy": null
+        },
+        "name": "balances_transfer_id_fkey",
+        "on_delete": "delete",
+        "on_update": null,
+        "primary_key?": true,
+        "schema": null,
+        "table": "transfers"
+      },
+      "size": null,
+      "source": "transfer_id",
+      "type": "binary"
+    },
+    {
+      "allow_nil?": false,
+      "default": "nil",
+      "generated?": false,
+      "primary_key?": false,
+      "references": {
+        "deferrable": false,
+        "destination_attribute": "id",
+        "destination_attribute_default": null,
+        "destination_attribute_generated": null,
+        "index?": false,
+        "match_type": null,
+        "match_with": null,
+        "multitenancy": {
+          "attribute": null,
+          "global": null,
+          "strategy": null
+        },
+        "name": "balances_account_id_fkey",
+        "on_delete": null,
+        "on_update": null,
+        "primary_key?": true,
+        "schema": null,
+        "table": "accounts"
+      },
+      "size": null,
+      "source": "account_id",
+      "type": "uuid"
+    }
+  ],
+  "base_filter": null,
+  "check_constraints": [],
+  "custom_indexes": [],
+  "custom_statements": [],
+  "has_create_action": true,
+  "hash": "71F6146A6CB681A42EFEB7E1DC739CA5BA76B42680273779E1C4AB2DECF656EA",
+  "identities": [
+    {
+      "all_tenants?": false,
+      "base_filter": null,
+      "index_name": "balances_unique_references_index",
+      "keys": [
+        {
+          "type": "atom",
+          "value": "account_id"
+        },
+        {
+          "type": "atom",
+          "value": "transfer_id"
+        }
+      ],
+      "name": "unique_references",
+      "nils_distinct?": true,
+      "where": null
+    }
+  ],
+  "multitenancy": {
+    "attribute": null,
+    "global": null,
+    "strategy": null
+  },
+  "repo": "Elixir.AshDoubleEntry.Test.Repo",
+  "schema": null,
+  "table": "balances"
+}