chore: Update schema.py and service.py to handle file serialization and deserialization (#2159)

Refactor the MessageModel class in schema.py to include methods for validating and serializing the 'files' field. This ensures that the 'files' field can be properly handled when it is a string or a list.

In service.py, update the query in the MonitorService class to include the 'files' field when retrieving messages from the database. This ensures that the 'files' field is included in the query results.

src/backend/base/langflow/services/monitor/schema.py

@@ -91,9 +91,17 @@ class MessageModel(DefaultModel):
     files: list[str] = []
 
     @field_validator("files", mode="before")
+    @classmethod
     def validate_files(cls, v):
         if isinstance(v, str):
-            return json.loads(v)
+            v = json.loads(v)
+        return v
+
+    @field_serializer("files")
+    @classmethod
+    def serialize_files(cls, v):
+        if isinstance(v, list):
+            return json.dumps(v)
         return v
 
     @classmethod

src/backend/base/langflow/services/monitor/service.py

@@ -140,7 +140,7 @@ class MonitorService(Service):
         order: Optional[str] = "DESC",
         limit: Optional[int] = None,
     ):
-        query = "SELECT index, flow_id, sender_name, sender, session_id, text, timestamp FROM messages"
+        query = "SELECT index, flow_id, sender_name, sender, session_id, text, files, timestamp FROM messages"
         conditions = []
         if sender:
             conditions.append(f"sender = '{sender}'")