Rails做单元测试时，我们自己手动去创建所有的fixtures会是个噩梦，有没有什么好的方案呢?
我们可以利用数据库里已有的数据，写一个rake tast来把数据库的数据复制出来到YAML文件里:
CreateFixturesFromLiveData/lib/tasks/extract_fixtures.rake

desc 'Create YAML test fixtures from data in an existing database.
Defaults to development database. Set RAILS_ENV to override.'

task :extract_fixtures => :environment do
  sql = "SELECT * FROM %s"
  skip_tables = ["schema_info"]
  ActiveRecord::Base.establish_connection
  (ActiveRecord::Base.connection.tables - skip_table).each do |table_name|
    i = "000"
    File.open("#{RAILS_ROOT}/test/fixtures/#{table_name}.yml", 'w') do |file|
      data = ActiveRecord::Base.connection.select_all(sql % table_name)
      file.write data.inject({}) {|hash, record|
        hash["#{table_name}_#{i.succ!}"] = record
        hash
      }.to_yaml
    end
  end
end

好了，现在我们运行rake extract_fixtures，则test/fixtures/目录下将生成每个表的数据的yml文件