Avoiding duplicate inserts?

rubyonrails-talk
1

I'm wondering if there is a good Rails solution to avoiding duplicate inserts with identical content. I know of the locking to prevent updates, but looking for something on inserts.

For example, say you have an API to a blog system that lets a caller post a comment. The client calls "addComment" with the same parameters (say, user_id and comment) twice and each request is handled by a different mongrel instance. How can the duplicate comment be prevented from being saved? They would be different rows, and I would like to avoid table locking. (In this example, the client can't be controlled, so it needs to be server-side.)

I believe that a validating on before_save is not enough because there would still be a window between the validation completing and writing the row since it is only the row that is locked.

Any suggestions would be appreciated.

Thanks,

-mike

2

not sure if that would work in your case, but what about unique keys in your database?

3

Sounds like a job for validates_uniqueness_of :comment, :scope=>:user

The double-submit issue is a matter to solve on the client (e.g., disable the submit button after it's clicked; clear the comment field, etc).

For now, I'd recommend that you take this simple approach and let the real users' use demonstrate that more needs to be done. I suspect you're concern (beyond this) is more theoretical than practical.