CS50 Lec7 - SqLite SameTime Update Error - Transaction


In a scenario, Bob and David clicked the like button on Instagram at the same time.
they all got the same value before it changed, like 1000.
So, after Bob clicked, and Added the like number, the result was 1001,
but same as David, got the previous value from the data base as 1000, so the result would not be 1002, but 1001.

How to resolve this problem?
We lock this process with transaction, the new command will not execute untill the last one complete (commit the transaction).

Transaction

db.execute("BEGIN TRANSACTION");
rows = db.execute("SELECT likes FROM posts WHERE id = ?", id);
like = row[0]["likes"];
db.execute("UPDATE POSTS SET likes = ? WHERE id = ?", likes + 1, id);
db.execute("COMMIT");
#SQL #sqllite #Transaction #cs50







你可能感興趣的文章

認識資料庫的推薦閱讀

認識資料庫的推薦閱讀

CSS-[box-shadow]-陰影效果

CSS-[box-shadow]-陰影效果

第 19 期 Python 程式設計入門-作業任務5

第 19 期 Python 程式設計入門-作業任務5






留言討論