Frederick Cheung questions

Frederick Cheung answers

• RSpec undefined method `request='
• has_and_belongs_to_many and unique index on association table generates "Duplicate entry" fail
• Ruby on Rails: Datatype foreign key
• What does this mean? *** "Delete" argument ":destroy," needs to be a number (Rails)
• How to write Cartesian Product in Ruby?
• Is there any difference in using up/down vs change/reversible methods in Rails migrations?
• How to choose an operator just one time, instead of repeating the test inside a loop?
• Can't start service with sudo since root user has no access to Ruby
• (ruby gems) warning: duplicated key at line 46 ignored: "index0"
• Explain the usage of procs in an rspec context