How to restrict updation from multiple users in windows froms

The issue is called concurrency, and is a huge issue for any system architect. Basically there are two courses that you can take. Pessimistic Concurrency and Optimistic Concurrency.

1. Pessimistic concurrency is where you actively put a lock on any object that is being updated. In your case, say one user opened the check out form, you would put a lock on the checkoutid column in your database, and no other user could access the check out till the first user was through and released the lock. The advantage of this is that it is easy to implement and you also know that no data can be overwritten unintentionally. The disadvantage of this is that if you have more than a few users, this system does not scale well, and if your user opens up the form, then goes to lunch, that table could be locked till they get back.

2. Optimistic concurrency is where you take into account that you will get 2 or more users updating the record at the same time, and you put into place a system whereby you check to see if the data has been changed since it was last retrieved, and you abort the transaction if it is true. In your case, you could maybe put a timestamp column in the table to be updated, and this column will be updated to the current time whenever the checkoutid is updated. When your user accesses the check out form, you retrieve the timestamp and keep it in memory. Then you would check the current timestamp each time you want to update checkoutid, and if it does not match your in memory timestamp then abort the transaction, or create a new checkoutid with the current data etc.

Hope this helps