Add transaction demo

api/operation.py

@@ -3,7 +3,7 @@ from .connection import g_conn_dict as conn
 
 def _get_current_transaction(name: str) -> Row | None:
     with conn[name].cursor(row_factory=dict_row) as cur:
-        cur.execute(f"select id from transaction_operation")
+        cur.execute(f"select * from transaction_operation")
         return cur.fetchone()
 
 def _get_current_transaction_id(name: str) -> int:
@@ -20,7 +20,6 @@ def _remove_operation(name: str, id: int) -> None:
         cur.execute(f"delete from transaction_operation where id = {id}") # this should not happen
         cur.execute(f"delete from snapshot_operation where id = {id}") # this may happen
         cur.execute(f"delete from operation where id = {id}")
-        return int(cur.fetchone()['id'])
 
 def _get_parents(name: str, id: int) -> list[int]:
     ids = [id]
@@ -81,14 +80,15 @@ def execute_undo(name: str, discard: bool = False) -> None:
     curr = _get_current_operation(name)
 
     # transaction control
-    tran = _get_current_transaction(name)
-    if int(tran['id']) >= 0:
-        if bool(tran['strict']): # strict mode disallow undo
-            print("Do not allow to undo in strict transaction mode!")
-            return
-        elif tran <= curr: # normal mode disallow undo start point, and there is foreign key constraint
-            print("Do not allow to undo transaction start point!")
-            return
+    if have_transaction(name):
+        tran = _get_current_transaction(name)
+        if tran != None and int(tran['id']) >= 0:
+            if bool(tran['strict']): # strict mode disallow undo
+                print("Do not allow to undo in strict transaction mode!")
+                return
+            elif int(tran['id']) >= curr: # normal mode disallow undo start point, and there is foreign key constraint
+                print("Do not allow to undo transaction start point!")
+                return
 
     row = _query_undo(name, curr)
     undo = row['undo']
@@ -183,7 +183,9 @@ def pick_snapshot(name: str, tag: str) -> None:
 # it may remove snapshot tag if snapshot in a rollback transaction
 
 def have_transaction(name: str) -> bool:
-    return _get_current_transaction_id(name) >= 0
+    with conn[name].cursor(row_factory=dict_row) as cur:
+        cur.execute(f"select * from transaction_operation")
+        return cur.rowcount > 0
 
 def start_transaction(name: str, strict: bool = False) -> None:
     if have_transaction(name):
@@ -203,11 +205,12 @@ def commit_transaction(name: str) -> None:
     _remove_transaction(name)
 
 def abort_transaction(name: str) -> None:
-    tran = _get_current_transaction_id(name)
-    if tran >= 0:
+    if not have_transaction(name):
         print("No active transaction!")
         return
 
+    tran = _get_current_transaction_id(name)
+
     curr = _get_current_operation(name)
     curr_parents = _get_parents(name, curr)