ActiveRecord的解析字符串日期时间？ [英] ActiveRecord parse string to datetime?

问题描述

如果我通过字符串到日期时间列，同时创造新的AR对象时，它会自动解析：

If I pass a String into Datetime column while creating new AR object, it will be automatically parse:

1.9.2p290 :011 > Movie.new(:release_date=>"21-Nov-1990")
 => #<Movie id: nil, release_date: "1990-11-21 00:00:00", created_at: nil, updated_at: nil>

如何的Rails 或的ActiveRecord ，做到这一点魔法？哪种方法不会使用？

How does Rails, or ActiveRecord, do this magic? Which method does it use?

推荐答案

Rails添加一个 TO_DATE 方法字符串。它的来源很简单：

Rails adds a to_date method to String. Its source is simple:

# File activesupport/lib/active_support/core_ext/string/conversions.rb, line 42
def to_date
  return nil if self.blank?
  ::Date.new(*::Date._parse(self, false).values_at(:year, :mon, :mday))
end

Date._parse 原产于红宝石（同样的方法被称为 Date.parse ），它的< A HREF =htt​​p://apidock.com/ruby/Date/_parse/class>其中真正的工作是做的。

Date._parse is native to Ruby (the same method is called by Date.parse) and it's where the real work is done.

它首先使用正则EX pression从字符串删除多余的符号，然后将其传递到其他的方法，如 _parse_eu ， _parse_iso ， _parse_dot 等。每个这些使用其自己的正常前pressions等方法，看它是否是它理解并从中提取的有意义的信息的日期。一旦其中的一个作品（即返回true），其余被跳过。最后，早在 _parse ，所提取的信息来建立一个日期和时间，做更多的工作，以找出像检查的一周内有无一天对12一年价值应该是指1912年或2012年。

It first uses a regular expression to remove extraneous symbols from the string, then passes it to other methods like _parse_eu, _parse_iso, _parse_dot and so on. Each of these uses its own regular expressions and other methods to see if it's a date that it understands and extract the meaningful information from it. Once one of them "works" (i.e. returns true), the rest are skipped. Finally, back in _parse, the extracted information is used to build a date and time, doing a little more work to figure out things like checking for the day of the week and whether a year value of "12" should mean 1912 or 2012.

该文档称这是一个启发式的方法，它可以被理解为它抛出一堆可能性墙上看到什么坚持。这是pretty的不良的记录，但运作得非常好。

The docs call this a heuristic method, which could be taken to mean it throws a bunch of possibilities at the wall to see what sticks. It's pretty poorly-documented but works remarkably well.

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