diff --git a/ir.py b/ir.py
index 7aa9aca..1456371 100644
--- a/ir.py
+++ b/ir.py
@@ -10,17 +10,23 @@ from trytond.pool import PoolMeta
 class Rule(metaclass=PoolMeta):
     __name__ = 'ir.rule'
 
+    @classmethod
+    def _context_modelnames(cls):
+        """ list of models to add 'user_id' to context
+        """
+        return ['cashbook.book', 'cashbook.line', 'cashbook.recon']
+
     @classmethod
     def _get_context(cls, model_name):
         context = super()._get_context(model_name)
-        if model_name in {'cashbook.book', 'cashbook.line', 'cashbook.recon'}:
+        if model_name in cls._context_modelnames():
             context['user_id'] = Transaction().user
         return context
 
     @classmethod
     def _get_cache_key(cls, model_name):
         key = super()._get_cache_key(model_name)
-        if model_name in {'cashbook.book', 'cashbook.line', 'cashbook.recon'}:
+        if model_name in cls._context_modelnames():
             key = (*key, Transaction().user)
         return key