feat: prevent deletion of membership fee type when used as default in settings

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