Be careful when you compare the GUID with a string

A GUID is a 128-bit number calculated so that it is globally unique after 100 nanoseconds (or so).

However, if you call guid.tostring(), it will return a string in low-case, meanwhile, the GUID in database will be in upper-case.

That could result in some weird problems, unfortunately, I met this kind of issue last week in a project developed in Euro.