Enforce unique URLs with Unique Index on the server?

[Yaakov-Belch]

Microscope tries to prevent duplicate URLs by checking the URL of a newly created post against the URLs already submitted to the data base. This technique is not fault-proof:

• We also need to check modifications of existing URLs. See issue #330. Even if you try to check this in some cases of modifications, you can easily forget one and still get duplicates. This is messy.
• If two separate users submit the same URL at the same time, a race condition could occur: The uniqueness checks for both posts may succeed before any of them is added to the data base --- allowing two posts with the same URL to enter the data base.

It seems to me that the correct approach is to Create a Unique MongoDB Index on the server and to just handle the exceptions thrown by invalid operations. I haven't tried this myself, though.

[tmeasday]

Yes. We should probably mention indices somewhere in the book too.