message_specific_error_classifier.rb

message_specific_error_classifier.rb

# Generates a module that can be used in a rescue clause
# in order to rescue errors that match a specific class
# and message. This is useful when there is a generic
# error like `Sequel::Mysql2Error` that we want to only rescue
# some instances of based on the message.
module MessageSpecificErrorClassifier
  def self.new(root_error, fragment)
    Module.new do
      define_singleton_method(:fragment) { fragment }
      define_singleton_method(:root_error) { root_error }

      define_singleton_method :=== do |raised_error|
        root_error === raised_error && raised_error.message.include?(fragment)
      end
    end
  end
end

DBExists = MessageSpecificErrorClassifier.new(
  Sequel::DatabaseError, "database exists"
)

DBDoesNotExist = MessageSpecificErrorClassifier.new(
  Sequel::DatabaseError, "database doesn't exist"
)

UnknownDB = MessageSpecificErrorClassifier.new(
  Sequel::DatabaseError, "Mysql2::Error: Unknown database"
)

def do_something
  foobar
rescue UnknownDB
  handle_it_somehow
end