improvement: don't destroy balances by default

documentation/dsls/DSL:-AshDoubleEntry.Transfer.md

@@ -21,7 +21,7 @@ An extension for creating a double entry ledger transfer. See the getting starte
 | [`account_resource`](#transfer-account_resource){: #transfer-account_resource .spark-required} | `module` |  | The resource to use for account balances |
 | [`pre_check_identities_with`](#transfer-pre_check_identities_with){: #transfer-pre_check_identities_with } | `module` |  | A domain to use to precheck generated identities. Required by certain data layers. |
 | [`balance_resource`](#transfer-balance_resource){: #transfer-balance_resource } | `module` |  | The resource being used for balances |
-| [`create_accept`](#transfer-create_accept){: #transfer-create_accept } | `atom \| list(atom)` |  | Additional attributes to accept when creating a transfer |
+| [`create_accept`](#transfer-create_accept){: #transfer-create_accept } | `atom \| list(atom)` | `[]` | Additional attributes to accept when creating a transfer |
 
 
 

documentation/tutorials/getting-started-with-ash-double-entry.md

@@ -91,6 +91,11 @@ defmodule YourApp.Ledger.Transfer do
     # configure the other resources it will interact with
     account_resource YourApp.Ledger.Account
     balance_resource YourApp.Ledger.Balance
+
+    # you only need this if you are using `postgres`
+    # and so cannot add the `references` block shown below
+
+    # destroy_balances? true
   end
 end
 ```
@@ -122,6 +127,10 @@ defmodule YourApp.Ledger.Balance do
   postgres do
     table "balances"
     repo YourApp.Repo
+
+    references do
+      reference :transfer, on_delete: :delete
+    end
   end
 
   balance do
@@ -161,6 +170,13 @@ defmodule YourApp.Ledger.Balance do
 end
 ```
 
+> ### cascading destroys {: .warning}
+>
+> If you are not using a data layer capable of automatic cascade
+> deletion, you must add `destroy_balances? true` to the `transfer`
+> resource! We do this with the `references` block in `ash_postgres`
+> as shown above.
+
 #### What does this extension do?
 
 - Adds the following attributes:

lib/transfer/changes/verify_transfer.ex

@@ -8,6 +8,14 @@ defmodule AshDoubleEntry.Transfer.Changes.VerifyTransfer do
   use Ash.Resource.Change
   require Ash.Query
 
+  def atomic(changeset, opts, context) do
+    if AshDoubleEntry.Transfer.Info.transfer_destroy_balances?(changeset.resource) do
+      {:error, "Cannot destroy a transfer atomically if balances must be destroyed manually"}
+    else
+      {:ok, change(changeset, opts, context)}
+    end
+  end
+
   def change(changeset, _opts, context) do
     if changeset.action.type == :update and
          Enum.any?(
@@ -19,24 +27,21 @@ defmodule AshDoubleEntry.Transfer.Changes.VerifyTransfer do
         "Cannot modify a transfer's from_account_id, to_account_id, or id"
       )
     else
-      changeset
-      |> Ash.Changeset.before_action(fn changeset ->
-        if changeset.action.type == :create do
-          timestamp = Ash.Changeset.get_attribute(changeset, :timestamp)
-
-          timestamp =
-            case timestamp do
-              nil -> System.system_time(:millisecond)
-              timestamp -> DateTime.to_unix(timestamp, :millisecond)
-            end
+      if changeset.action.type == :create do
+        timestamp = Ash.Changeset.get_attribute(changeset, :timestamp)
 
-          ulid = AshDoubleEntry.ULID.generate(timestamp)
+        timestamp =
+          case timestamp do
+            nil -> System.system_time(:millisecond)
+            timestamp -> DateTime.to_unix(timestamp, :millisecond)
+          end
 
-          Ash.Changeset.force_change_attribute(changeset, :id, ulid)
-        else
-          changeset
-        end
-      end)
+        ulid = AshDoubleEntry.ULID.generate(timestamp)
+
+        Ash.Changeset.force_change_attribute(changeset, :id, ulid)
+      else
+        changeset
+      end
       |> maybe_destroy_balances(context)
       |> Ash.Changeset.after_action(fn changeset, result ->
         from_account_id = Ash.Changeset.get_attribute(changeset, :from_account_id)
@@ -192,7 +197,7 @@ defmodule AshDoubleEntry.Transfer.Changes.VerifyTransfer do
         )
         |> case do
           %Ash.BulkResult{status: :success} -> changeset
-          %Ash.BulkResult{errors: errors} -> {:error, Ash.Changeset.add_error(changeset, errors)}
+          %Ash.BulkResult{errors: errors} -> Ash.Changeset.add_error(changeset, errors)
         end
       end)
     else

lib/transfer/transfer.ex

@@ -23,6 +23,11 @@ defmodule AshDoubleEntry.Transfer do
         type: {:wrap_list, :atom},
         default: [],
         doc: "Additional attributes to accept when creating a transfer"
+      ],
+      destroy_balances?: [
+        type: :boolean,
+        doc: "Whether or not balances must be manually destroyed. See the getting started guide for more.",
+        default: false
       ]
     ]
   }

lib/transfer/transformers/add_structure.ex

@@ -37,6 +37,11 @@ defmodule AshDoubleEntry.Transfer.Transformers.AddStructure do
       AshDoubleEntry.Transfer.Info.transfer_account_resource!(dsl),
       attribute_writable?: true
     )
+    |> Ash.Resource.Builder.add_new_relationship(
+      :has_many,
+      :balances,
+      AshDoubleEntry.Transfer.Info.transfer_balance_resource!(dsl)
+    )
     |> Ash.Resource.Builder.add_action(:create, :transfer,
       accept:
         [:amount, :timestamp, :from_account_id, :to_account_id] ++
@@ -46,6 +51,7 @@ defmodule AshDoubleEntry.Transfer.Transformers.AddStructure do
       pagination: Ash.Resource.Builder.build_pagination(keyset?: true)
     )
     |> Ash.Resource.Builder.add_change({AshDoubleEntry.Transfer.Changes.VerifyTransfer, []},
+      only_when_valid?: true,
       on: [:create, :update, :destroy]
     )
   end