diff --git a/backend/models/base_doc.py b/backend/models/base_doc.py
index 77fca47..bd6722d 100644
--- a/backend/models/base_doc.py
+++ b/backend/models/base_doc.py
@@ -15,10 +15,18 @@ class QueryExpression:
     def __init__(self, field_name: str):
         self.field_name = field_name
 
+    def __getattr__(self, name: str) -> 'QueryExpression':
+        """Handle nested field access like FLID.identity"""
+        return QueryExpression(f"{self.field_name}.{name}")
+
     def __eq__(self, other: Any) -> Dict[str, Any]:
         """Handle field == value comparisons"""
         return {self.field_name: other}
 
+    def __deepcopy__(self, memo):
+        """Support deepcopy for Pydantic field processing"""
+        return QueryExpression(self.field_name)
+
     def __ne__(self, other: Any) -> Dict[str, Any]:
         """Handle field != value comparisons"""
         return {self.field_name: {"$ne": other}}
@@ -61,6 +69,10 @@ class FieldDescriptor:
             raise TypeError(f"Field {self.field_name} must be {self.field_type}")
         instance.__dict__[self.field_name] = value
 
+    def __deepcopy__(self, memo):
+        """Support deepcopy for Pydantic field processing"""
+        return FieldDescriptor(self.field_name, self.field_type)
+
 
 class FieldCondition:
     """Represents a field condition for MongoDB queries"""
@@ -84,18 +96,9 @@ _tenant_db_context: contextvars.ContextVar[Optional[AsyncIOMotorDatabase]] = con
 class QueryModelMeta(ModelMetaclass):
     """Metaclass: automatically create FieldDescriptor for model fields"""
     def __new__(cls, name: str, bases: tuple, namespace: dict):
-        # Get model field annotations (like name: str -> "name" and str)
-        annotations = namespace.get("__annotations__", {})
-
         # Create the class first using Pydantic's metaclass
+        # Don't add FieldDescriptor during __new__ to avoid interfering with Pydantic's processing
         new_class = super().__new__(cls, name, bases, namespace)
-
-        # After Pydantic processes the fields, add the descriptors as class attributes
-        for field_name, field_type in annotations.items():
-            if field_name != 'id':  # Skip the id field as it's handled specially
-                # Add the descriptor as a class attribute
-                setattr(new_class, field_name, FieldDescriptor(field_name, field_type))
-
         return new_class
 
     def __getattr__(cls, name: str):