lib/membership_fees/membership_fee_type.ex

@@ -120,6 +120,28 @@ defmodule Mv.MembershipFees.MembershipFeeType do
                end
              end,
              on: [:destroy]
+
+    # Prevent deletion if used as default in settings
+    validate fn changeset, _context ->
+               if changeset.action_type == :destroy do
+                 require Ash.Query
+
+                 setting_count =
+                   Mv.Membership.Setting
+                   |> Ash.Query.filter(default_membership_fee_type_id == ^changeset.data.id)
+                   |> Ash.count!()
+
+                 if setting_count > 0 do
+                   {:error,
+                    message: "Cannot delete membership fee type: it's used as default in settings"}
+                 else
+                   :ok
+                 end
+               else
+                 :ok
+               end
+             end,
+             on: [:destroy]
   end
 
   attributes do

test/membership_fees/membership_fee_type_integration_test.exs

@@ -123,6 +123,24 @@ defmodule Mv.MembershipFees.MembershipFeeTypeIntegrationTest do
       error_message = extract_error_message(error)
       assert error_message =~ "cycle(s) reference"
     end
+
+    test "cannot delete when used as default in settings" do
+      fee_type = create_fee_type(%{interval: :yearly})
+
+      # Set as default in settings
+      {:ok, settings} = Mv.Membership.get_settings()
+
+      settings
+      |> Ash.Changeset.for_update(:update_membership_fee_settings, %{
+        default_membership_fee_type_id: fee_type.id
+      })
+      |> Ash.update!()
+
+      # Try to delete
+      assert {:error, error} = Ash.destroy(fee_type)
+      error_message = extract_error_message(error)
+      assert error_message =~ "used as default in settings"
+    end
   end
 
   describe "settings integration" do

test/membership_fees/membership_fee_type_test.exs

@@ -228,6 +228,22 @@ defmodule Mv.MembershipFees.MembershipFeeTypeTest do
       error_message = extract_error_message(error)
       assert error_message =~ "cycle" or error_message =~ "referenced"
     end
+
+    test "cannot delete when used as default in settings", %{fee_type: fee_type} do
+      # Set as default in settings
+      {:ok, settings} = Mv.Membership.get_settings()
+
+      settings
+      |> Ash.Changeset.for_update(:update_membership_fee_settings, %{
+        default_membership_fee_type_id: fee_type.id
+      })
+      |> Ash.update!()
+
+      # Try to delete
+      assert {:error, error} = Ash.destroy(fee_type)
+      error_message = extract_error_message(error)
+      assert error_message =~ "used as default in settings"
+    end
   end
 
   # Helper to check if an error occurred on a specific field