删除计划时必须先删除子计划

app/Http/Controllers/API/PlanController.php

@@ -120,6 +120,9 @@ class PlanController extends Controller
     public function destroy(string $id)
     {
         $plan = Plan::findOrFail($id);
+        if(!empty($plan->children()->first())){
+            throw new \Exception("Please remove the sub-level plan.");
+        }
 
         $plan->delete();