mysql - 引发 MysqlError; raise Mysql::Error 都有效，这是怎么发生的？

Question

问候，

我正在研究 mysql 异常，遇到了这个有趣的问题，其中引发的异常响应两个不同的异常名称。这怎么发生的？

-丹尼尔

#!/usr/bin/env ruby

require 'rubygems'
require 'mysql'
require 'yaml'
require 'pp'

$config = YAML.load_file 'database.yml'

class ExceptionPrinter 

  def self.print msg, e
    puts msg
    pp e
  end

end

# sample connect: dbh = Mysql.real_connect $config['database']['host'], $config['database']['user'], $config['database']['password'], $config['database']['db'], $config['database']['port']

# test 1 - what class is thrown?

begin

  puts "Starting test - MysqlError"
  dbh = Mysql.real_connect $config['database']['host'], $config['database']['user'], $config['database']['password'], $config['database']['db']
  puts "Error: Code did not throw exception"

rescue MysqlError => e # MysqlError is not a valid exception catch

  ExceptionPrinter.print "MysqlError", e

rescue Exception => e

  ExceptionPrinter.print "Exception class", e

end

# test 2 - What class is thrown?

begin

  puts "Starting test - Mysql::Error"
  dbh = Mysql.real_connect $config['database']['host'], $config['database']['user'], $config['database']['password'], $config['database']['db']
  puts "Error: Code did not throw exception"

rescue Mysql::Error => e

  ExceptionPrinter.print "Mysql::Error", e

rescue Exception => e

  ExceptionPrinter.print "Exception class", e

end

- 输出

开始测试 - MysqlError MysqlError

开始测试 - Mysql::Error Mysql::Error

Answer 1

看起来一个只是另一个的别名：

Mysql::Error
# => Mysql::Error
MysqlError
# => Mysql::Error

基于此，我期望在 MySQL gem 的某个地方有这样一行：

class Mysql
  MysqlError = Mysql::Error
end

这意味着 MysqlError 是一个定义为 Mysql::Error 类的常量。