enh: use sqlalchemy offset and limit to fetch messages

CHANGELOG.md

@@ -6,7 +6,7 @@
 
 ### Changed
 
-
+1. Use SQLAlchemy offset and limit to fetch only required messages.
 
 ### Fixed
 

src/memorytext/services/message_service.py

@@ -1,6 +1,6 @@
 from __future__ import annotations
 from sqlalchemy.orm import Session
-from sqlalchemy import select
+from sqlalchemy import select, func
 
 from memorytext.models.core import Message
 from memorytext.db import get_db
@@ -10,23 +10,19 @@ def get_messages(
     conversation_id: int | None, limit: int = 10, offset: int = 0
 ) -> tuple[list, int]:
     engine = get_db()
-    count = limit + offset
     with Session(engine) as session:
-        stmt = (
+        stmt = select(func.count(Message.id)).where(
+            Message.conversation_id == conversation_id
+        )
+        total = session.scalar(stmt) or 0
+
+        stmt_2 = (
             select(Message)
             .where(Message.conversation_id == conversation_id)
             .order_by(Message.timestamp.asc())
+            .limit(limit)
+            .offset(offset)
         )
-        message_list = list(session.scalars(stmt).fetchall())
-    if message_list is not None:
-        total = len(message_list)
-    else:
-        total = 0
-    if message_list is not None and offset >= total:
-        return [], total
-    elif message_list is not None and count >= total:
-        return message_list[offset:], total
-    elif message_list is not None:
-        return message_list[offset:count], total
-    else:
-        return [], total
+        message_list = list(session.scalars(stmt_2).fetchall())
+        session.expunge_all()
+        return message_list, total

src/memorytext/views/chat_view.py

@@ -6,8 +6,7 @@
 
 from memorytext.models.message_list import MessageList
 from memorytext.services import message_service
-from memorytext.delegates.message_list import MessageDelegate
-
+import memorytext.delegates.message_list as msg_delegate
 
 if TYPE_CHECKING:
     from collections.abc import Callable
@@ -23,7 +22,8 @@ def __init__(self):
         self.setSpacing(10)
         self.message_model = MessageList(None, message_service.get_messages)
         self.setModel(self.message_model)
-        self.setItemDelegate(MessageDelegate())
+        self.delegate = msg_delegate.MessageDelegate(self)
+        self.setItemDelegate(self.delegate)
         self.setWordWrap(True)
         self.setUniformItemSizes(False)
         self.setFocusPolicy(Qt.NoFocus)  # pyright: ignore[reportAttributeAccessIssue]