diff --git a/app/library/App/Controllers/UserController.php b/app/library/App/Controllers/UserController.php
index 47794a6..f234111 100755
--- a/app/library/App/Controllers/UserController.php
+++ b/app/library/App/Controllers/UserController.php
@@ -4,6 +4,8 @@ namespace App\Controllers;
 
 use App\Model\Project;
 use App\Model\User;
+use PhalconApi\Constants\ErrorCodes;
+use PhalconApi\Exception;
 use PhalconRest\Mvc\Controllers\CrudResourceController;
 
 class UserController extends CrudResourceController
@@ -55,7 +57,6 @@ class UserController extends CrudResourceController
         if (!$data || count($data) == 0) {
             return $this->onNoDataProvided();
         }
-
         if (!$this->postDataValid($data, false)) {
             return $this->onDataInvalid($data);
         }
@@ -107,4 +108,27 @@ class UserController extends CrudResourceController
         }
     }
 
-}
+    protected function postDataValid($data, $isUpdate)
+    {
+        $input_name = $data['username'];
+        if (!empty($input_name))
+        {
+
+            $same_user = User::find(["username = '".$input_name."'"]);
+            if (isset($same_user[0]) && !empty($same_user[0]->username))
+            {
+                return false;
+            }
+
+        }
+
+        return true;
+    }
+
+    protected function onDataInvalid($data)
+    {
+        $msg = 'Post-data is invalid, trying to use non-unique value of `username`';
+        throw new Exception(ErrorCodes::POST_DATA_INVALID, $msg, ['data' => $data]);
+    }
+
+}
\ No newline at end of file
--
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