如何值指派到Rails的ActiveRecord的布尔字段时，投？ [英] How are values cast when assigning to a Boolean field in Rails ActiveRecord?

问题描述

短版我的问题

在Rails的ActiveRecord的，如果我有一个布尔领域，我给它分配类似 ABC 或 2 ，那么它就会立即转换为假。该值 1 被转换为真正和无遗体为无。为什么会出现这样的情况？我在哪里可以找到Rails文档（或Ruby文档），说明这种行为？

In Rails ActiveRecord, if I have a Boolean field and I assign it something like "abc" or 2, then it gets immediately cast to false. The value 1 is cast to true, and nil remains as nil. Why is this the case? Where can I find Rails documentation (or Ruby documentation) that explains this behavior?

我的问题的龙版

我难以理解的Rails如何处理尝试在Rails模型值分配给布尔字段。举例来说，假设我有一个有一个名为字符串字段网​​站模式：域名并称为布尔字段：can_ssl

I am having difficulty understanding how Rails handles attempts to assign values to a Boolean field in a Rails model. For example, let's say I have a Website model that has a String field called :domain and a Boolean field called :can_ssl.

我的迁移是这样的：

class CreateWebsites < ActiveRecord::Migration
  def change
    create_table :websites do |t|
      t.string :domain
      t.boolean :can_ssl, :default => false

      t.timestamps
    end
  end
end

在我的模型文件，我添加一些验证规则，所以它看起来是这样的：

In my model file, I add some validation rules, so it looks like this:

class Website < ActiveRecord::Base
  validates :domain, :presence => true
  validates :can_ssl, :inclusion =>  { :in => [true, false] }
end

就这么简单。基于我做了什么，我的希望是：can_ssl 只能设置为值真实或假，没有别的。还有什么会导致是否有效？是假。

Simple enough. Based on what I've done, I'm expecting that :can_ssl can only be set to the values true or false, and nothing else. Anything else would result in valid? being false.

但是，一旦我开始在控制台中打转转，我注意到，早在实际赋值语句，我提供的价值正在被改写为真正或假（或无）。什么是管理一个价值如何被转换为规则的布尔？

But once I start playing around in the console, I notice that, as early as the actual assignment statement, the value I provide is being recast to true or false (or nil). What are the rules governing how a value gets cast as a Boolean?

从控制台的例子：

w = Website.new
w.domain = 'stackoverflow.com'
w.can_ssl = true
w.can_ssl    # => true
w.valid?     # => true

w.can_ssl = nil
w.can_ssl    # => nil
w.valid?     # => false (so far so good)

w.can_ssl = 'abc'
w.can_ssl    # => false (How did 'abc' become the value false?)
w.valid?     # => true

w.can_ssl = 1
w.can_ssl    # => true (I guess it makes sense that 1 casts to true)
w.valid?     # => true

w.can_ssl = 2
w.can_ssl    # => false (But anything other than 1 casts to false?)
w.valid?     # => true

那么，根据什么我迄今所做的，我的认为的我可以得出以下结论：

So, based on what I've done so far, I think I can conclude the following:

• 在当前分配值 1 或真正到布尔字段，该值将立即得到转换为真正，然后分配。


• 当指定无到布尔字段，字段被实际分配零。


• 当指定别的（如字符串或任意数量不是 1 ），则该值将立即得到转换为假。

• When assigning the value 1 or true to a Boolean field, the value will immediately get cast as true and then assigned.
• When assigning nil to a Boolean field, the field is actually assigned nil.
• When assigning anything else (such as a String or any number that is not 1), then the value will immediately get cast as false.

难道我的理解是正确的？我缺少什么？

Am I understanding that correctly? Am I missing anything?

我很难找到文档中轨布尔字段类型，它可以给我澄清这一点。

I'm having difficulty finding documentation the Boolean field type in Rails which can give me clarification on this.

推荐答案

这是的ActiveRecord的肠子做：专门与

This is done in the bowels of ActiveRecord: specifically with

ActiveRecord::ConnectionAdapters::Column.value_to_boolean

至少在我的rails版本（可能是较新版本的地方略有不同）。

at least in my version of rails (it may be somewhere slightly different in more recent versions).

下面是源在我的版本

    # File activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb, line 144
    144:         def value_to_boolean(value)
    145:           if value.is_a?(String) && value.blank?
    146:             nil
    147:           else
    148:             TRUE_VALUES.include?(value)
    149:           end
    150:         end

在这里TRUE_VALUES被定义为

where TRUE_VALUES is defined as

#activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb:10:      
TRUE_VALUES = [true, 1, '1', 't', 'T', 'true', 'TRUE'].to_set

1，0，f和t的有没有，因为流行的DBMS的如MySQL和放大器; PostgreSQL里，用来存储布尔变量为0/1，和f/T分别。

1, 0, "f" and "t" are there because of popular DBMS's like MySql & PostgreSql, which store bools as 0/1 and "f"/"t" respectively.

值得注意的是这之间的区别，什么传递一个如果中的Ruby / Rails，即是truthy或falsy值测试（falsy的价值观会失败的，如果考truthy值将通过它）。

It's worth noting the difference between this and what passes an "if" test in Ruby/Rails, ie values that are "truthy" or "falsy" ("falsy" values will fail an if test, "truthy" values will pass it).

在Ruby中，无和假是falsy字面上的任何其他（包括0，空数组，空字符串，空哈希等）是truthy。所以，有什么之间被认为truthy一个巨大的差距/红宝石falsy，什么是保存为真/假为布尔数据库列。

In Ruby, nil and false are "falsy" and literally anything else (including 0, empty arrays, empty strings, empty hashes etc) is "truthy". So, there's a massive disparity between what is deemed truthy/falsy in ruby and what is saved as true/false to a boolean database column.

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