在 ruby​​ 1.9 和 CSV::Writer 中编写 csv

Question

我有一个代码可以在 ruby​​ 1.87 上正常工作，但不能在 ruby​​ 1.9 上工作。它说 CSV::Writer 未声明，但它仍然是 rdoc 的一部分。在 fastcsv 合并之后，csv api 是否发生了变化？

我的代码：

require 'csv'

def self.export_csv
 file_name = File.join(RAILS_ROOT, 'public','csv',"#{start_date_f}_#{end_date_f}.csv")
 return file_name if File.exist?(file_name)
 @results = find(:all)
 header_row = []
 outfile = File.open(file_name, 'wb')
 CSV::Writer.generate(outfile) do |csv|
      header_row = ['gateway_id','created', 'gateway_status_id', 'panel_id',  'panel_status','volts_out', 'amps_out', 'temp','aid' ,'sid', 'pisid']
      csv << header_row
  end
end

我收到的错误：NameError: uninitialized constant CSV::Writer

请注意，require 'csv' 在那里。我在我的控制台中尝试它，当我执行 require 'csv' 时，它可以工作，但是一旦我调用 CSV::Writer 我就会收到该错误。 这段代码在 ruby​​ 1.87 上运行良好，所以它让我认为这是一个 ruby​​ 1.9 csv 问题，因为它与 fastCSV 合并。

Answer 1

csv 库仍然存在，但 CSV::Writer 不存在。根据 1.9.0 中的 csv.rb：

# I'm sure I'll miss something, but I'll try to mention most of the major
# differences I am aware of, to help others quickly get up to speed:
#
# === CSV Parsing
#
# * This parser is m17n aware.  See CSV for full details.
# * This library has a stricter parser and will throw MalformedCSVErrors on
#   problematic data.
# * This library has a less liberal idea of a line ending than CSV.  What you
#   set as the <tt>:row_sep</tt> is law.  It can auto-detect your line endings
#   though.
# * The old library returned empty lines as <tt>[nil]</tt>.  This library calls
#   them <tt>[]</tt>.
# * This library has a much faster parser.
#
# === Interface
#
# * CSV now uses Hash-style parameters to set options.
# * CSV no longer has generate_row() or parse_row().
# * The old CSV's Reader and Writer classes have been dropped.
# * CSV::open() is now more like Ruby's open().
# * CSV objects now support most standard IO methods.
# * CSV now has a new() method used to wrap objects like String and IO for
#   reading and writing.
# * CSV::generate() is different from the old method.
# * CSV no longer supports partial reads.  It works line-by-line.
# * CSV no longer allows the instance methods to override the separators for
#   performance reasons.  They must be set in the constructor.

稍后，有一个如何逐行编写的示例（以及其他编写方法）：

# === To a File
#
#   CSV.open("path/to/file.csv", "wb") do |csv|
#     csv << ["row", "of", "CSV", "data"]
#     csv << ["another", "row"]
#     # ...
#   end