fix bug

bot_db.py

@@ -238,17 +238,16 @@ async def message_file(room: MatrixRoom, event: RoomMessageFile):
     assert isinstance(resp.body, bytes)
     md5 = hashlib.md5(resp.body).hexdigest()
 
-    document_fetch_result = await client.db.execute(
-        query="select content from documents where md5 = :md5;", values={"md5": md5}
+    document_fetch_result = await client.db.fetch_one(
+        query="select content from documents where md5 = :md5 lilmit 1;",
+        values={"md5": md5},
     )
-    document_alreadly_exists = len(document_fetch_result) == 0
 
     # get content
-    content = ""
+    content = document_fetch_result[0] if document_fetch_result else ""
     # document not exists
-    if not document_alreadly_exists:
+    if content:
         print("document", md5, "alreadly exists")
-        content = document_fetch_result[0][0]
     else:
         if mimetype == "text/plain" or mimetype == "text/markdown":
             content = resp.body.decode()