Uniqueness of a field

You could create a special SAIL component for this kind of value that already includes the validation. So a designer will not be able to forget it.

And the validation itself still should be manual?

With database constraint the error message will appear in the Alerts and user will not see it.

Two possible ways:
1) Add a validation which checks by querying database if the entered value already exists in DB. Problem is that another user could enter the same value at this time and the check would be OK for both.

2) Directly write the data to DB in the saveInto (a!writeToDatastoreEntity()) and react on failure/success of the operation. This way two users cannot enter the same value at the same time.

Thanks!

From my point of view option 1 is preferable in conjunction with database constraint. Option 2 is harder to insert into some process with additional error handling.

You could also validate just before the database write, and return to the form if the value is no longer unique.

I'm curious as the requirement though - why would a user need to enter a value that must be unique? Is it a name of some sort?

Option 2 is actually not that hard to implement directly in SAIL and would be best out of a user perspective. You also would not need to handle errors in DB.

Sorry: You also would not need to handle errors in DB. -> You also would not need to handle errors in process

Another thought - if the row already exists and you're feeling ambitious, you could implement pessimistic locking. What Stefan has suggested is already a sort of optimistic locking, i guess! :)

How can answer to someone on this forum? It's hard to understand talking to several people where are answers to me.

> I'm curious as the requirement though - why would a user need to enter a value that must be unique? Is it a name of some sort?

It's a pretty common requirement for an object name to be unique.