Rails不会转换时区（PostgreSQL） [英] Rails doesn't convert timezone (PostgreSQL)

问题描述

我对时区和postgresql数据库（Rails 3.0.4，PostgreSQL 9.0）有问题。我正在使用自定义范围，在其中添加了一些条件，进行了连接等。

I have a problem with timezones and a postgresql db (Rails 3.0.4, PostgreSQL 9.0). I'm using a custom scope, in which I append some conditions, do joins etc.pp.

问题是，Rails不会将时间转换为我的时间当地时区。
以下是范围的代码：

The problem is, that Rails don't convert the times to my local timezone. Here is the code of the scope:

  scope :with_activities_within_range_in_week, lambda{ |latMin, lngMin, latMax, lngMax, date|
    select("date_trunc('day', activities.starting_at) as date,
      count(activities.id) as value
    ") \
    .within(latMin, lngMin, latMax, lngMax) \
    .joins(:activities) \
    .merge(Activity.in_week(date)) \
    .group("date") \
    .order("date")
  }

内部方法检查范围， Activity.in_week范围返回以下内容：

The within method checks for ranges, the Activity.in_week scope returns this:

where("activities.starting_at >= ? AND activities.starting_at < ?", start, stop)

然后在select语句中，我想今天删节starting_at字段。

And in the select statement, I want to trunc the starting_at field to day.

我在日期字段中得到以下输出：

I'm getting the following output for the date field:

2011-04-07 18:48:32
2011-04-02 14:07:20
2011-04-02 14:06:49

很遗憾，它不包含时区。当我尝试通过正常 Rails函数访问模型时，它会起作用：

Unfortunately it doesn't include the timezone. When I try to access my model through the "normal" Rails functions, it works:

puts Activity.first.starting_at
-> 2011-04-15 06:47:55 +0200

我在做什么错？希望有人能帮忙！

What I'm doing wrong? Hope someone can help!

thx，
晚礼服

thx, tux

推荐答案

您的数据库正在将时间戳存储在UTC中（应如此）。当ActiveRecord知道有时间戳时，它将进行时区调整。因此，当您这样说：

Your database is storing your timestamps in UTC (as it should). ActiveRecord is making timezone adjustments when it knows that it has a timestamp; so, when you say this:

puts Activity.first.starting_at

AR知道 starting_at 是一个时间戳，因此将时间戳实例化为 ActiveSupport :: TimeWithZone 实例，该类将应用时区调整。但是，当您这样说：

AR knows that starting_at is a timestamp so it instantiates the timestamp as an ActiveSupport::TimeWithZone instance and that class applies the timezone adjustment. But, when you say this:

select("date_trunc('day', activities.starting_at) as date ...

AR不会解析SQL以找出 date_trunc 将返回一个时间戳，AR甚至都不知道 date_trunc 是什么意思，AR只会从数据库中看到一个字符串，并将其传递给您无需任何解释，就可以自己随意将字符串提供给 ActiveSupport :: TimeWithZone （或您最喜欢的时间处理类）：告诉AR事情没有错

AR isn't going to parse the SQL to figure out that date_trunc will return a timestamp, AR doesn't even know what date_trunc means. AR will just see a string coming out of the database and it will hand it to you without interpretation. You are free to feed that string to ActiveSupport::TimeWithZone (or your favorite time handling class) yourself: there's nothing wrong with telling AR things that it does not and cannot know on its own.

路轨很聪明，但不是魔术。

Rails is clever but it isn't magic.

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