With ActiveRecord as it currently is, you get the same error for
anything that might go wrong in the database,
ActiveRecord::InvalidStatement. That’s rather undistinctive, considering
that there are some problems only the database server can recognize, in
particular violated uniqueness and foreign key constraints.
If specific exceptions for these tow latter error conditions would help
you in your code, or if you are interested in the topic in general,
please review the following ticket and patch
Please state your opinion and/or support, for otherwise the issue might
be delayed interminably.