1. In the book borrowing record table, the field of "scheduled book return date" is added, which is automatically filled in every book borrowing operation.

2. Add "Lock Date" in the user table. If the book is returned after the scheduled book return date, the Lock Date in the user table will be filled with the current date +5 days.

3. When borrowing books, first judge whether the lock date is empty (if it is empty, the borrowing is normal); If it is not empty, judge whether the locking date is later than the current date; If so, refuse to borrow books. If the current date is later than the "lock date", it means that the lock-up period has passed and you can borrow normally.

The ideas given above should solve your problem!