gistfile1.txt

irb(main):004:0> User.count
=> 2
irb(main):005:0> User.create(:email => nil)
=> #<User _id: 4b581254a047455f06000001, >
irb(main):006:0> User.create!(:email => nil)
=> #<User _id: 4b581258a047455f06000002, >
irb(main):007:0> User.create!(:email => nil)
=> #<User _id: 4b58125aa047455f06000003, >
irb(main):008:0> User.create!(:email => nil)
=> #<User _id: 4b58125ba047455f06000004, >
irb(main):009:0> User.count
=> 2


# hint - there is a unique index and NO WAY to ask mongoid to raise an error.  it simply lies and returns an unsaved object.