选择特定的属性

#<Example example_id: 13, example2_id: 81, year: 2000, january: 12, february: 3, march: 3, april: 4, may: 5, june: 2, july: 4, august: 24, september: 4, october: 24, november: 4, december: 4>

我想把几个月的价值观像这样的数组：选择特定的属性

array_example = [12, 3, 3, 4, 5, 2, 4, 24, 4, 24, 4, 4]

我知道我能做到这一点（下面的例子），但我希望有一个更好的办法。

example.attributes.each do |attr_name, attr_value| 
     if attr_name == "january" || attr_name == "february" || attr_name == "march" || 
     attr_name == "april" || attr_name == "may" || attr_name == "june" || 
     attr_name == "july" || attr_name == "august" || attr_name == "september" || 
     attr_name == "october" || attr_name == "november" || attr_name == "december" 
        @array_example << attr_value 
     end 
    end

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2016-02-10 volt

Hash#values_at是正是这一点：

example.attributes.values_at(:january, :february, :march, :april, :may, :june, :july, :august, :september, :october, :november, :december) 
# => [12, 3, 3, 4, 5, 2, 4, 24, 4, 24, 4, 4]

这也可能是最好把月份名称在恒定（例如，在你的榜样模型），如果仅用于可读性，例如：

MONTH_ATTRS = %i[ january february march  april 
        may  june  july  august 
        september october november december ] 
# Or... 
MONTH_ATTRS = Date::MONTHNAMES.drop(1).map {|m| m.downcase.to_sym }

（后者使用Ruby的内置Date::MONTHNAMES常量; drop(1)是必要的，因为Date::MONTHNAMES[0]是nil，想必所以一月将索引1）

然后：

example.attributes.values_at(*Example::MONTH_ATTRS)

附：如果你宁愿有一个哈希不是一个数组，你可以使用Hash#slice从的ActiveSupport：

example.attributes.slice(*Example::MONTH_ATTRS) 
# => { :january => 12, :february => 3, :march => 3, :april => 4, 
#  :may => 5,  :june => 2,  :july => 4,  :august => 24, 
#  :september => 4, :october => 24, :november => 4, :december => 4 }

P.P.S.如果你不使用模型对象进行其他任何事情 - 例如。你只是想月份值，没有别的，你应该在你的查询中使用ActiveRecord::Calculations#pluck，例如：

Example.where(...).pluck(*Example::MONTH_ATTRS)

pluck告诉ActiveRecord的，只是返回，而不是实例化和返回为例模型对象的属性值。

来源

2016-02-10 16:51:04

months = %w(january february march) 
months.include? attr_name

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2016-02-10 16:44:10 Ursus

作为它的每一个月份的名称可能是最容易使用日期的月份名称不变'个月=日期:: MONTHNAMES.reject。（：无）地图（：downcase）' –

monthnames = %w(january february march april may june july august september october november december) 
example_attributes.each do |attr_name, attr_value| 
    if monthnames.include?(attr_name) 
    @array_example << attr_value 
    end 
end

@array_example += monthnames.collect{|monthname| example.attributes[monthname]}.reject(&:blank?)

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2016-02-10 16:48:50

MONTHS = %w(january february march april may june july august september october november december) 

example.attributes.slice(*MONTHS) 
=> {january: 12, february: 3, march: 3, april: 4, may: 5, june: 2, july: 4, august: 24, september: 4, october: 24, november: 4, december: 4} 
example.attributes.slice(*MONTHS).values 
=> [12, 3, 3, 4, 5, 2, 4, 24, 4, 24, 4, 4]

来源

2016-02-10 17:38:46

选择特定的属性

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