从ActiveRecord模型集合构建哈希

Question

我正在尝试从模型中构建哈希.

这是我想要构建的哈希类型.

{"United Sates" => "us", "United Kingdom" => "uk" .....}

我已经尝试了很多方法,现在我只是绕圈子走了.

以下是我的一些不良尝试.

select = Array.new
countries.each do |country|
  # select.push({country.name => country.code })
  # select[country.name][country.code]
end

h = {}

countries.each do |c|
  # h[] = {c.name => c.code}
  # h[] ||= {} 
  # h[][:name] = c.name
  # h[][:code] = c.code 
  #h[r.grouping_id][:name] = r.name
  # h[r.grouping_id][:description] = r.description
end

请一些人建议.

谢谢

Answer 1

以下是一些单线替代方案:

# Ruby 2.1+
name_to_code = countries.map{ |c| [c.name,c.code] }.to_h

# Ruby 1.8.7+
name_to_code = Hash[ countries.map{ |c| [c.name,c.code] } ]

# Ruby 1.8.6+
name_to_code = Hash[ *countries.map{ |c| [c.name,c.code] }.flatten ]

# Ruby 1.9+
name_to_code = {}.tap{ |h| countries.each{ |c| h[c.name] = c.code } }

# Ruby 1.9+
name_to_code = countries.to_a.each_with_object({}){ |c,h| h[c.name] = c.code }

感谢@ Addicted的评论如下:

# Ruby 1.8+
name_to_code = countries.inject({}){ |r,c| r.merge c.name=>c.code }

Answer 2

使用Rails 4,您可以简单地执行:

country_codes = Hash[Country.pluck(:name, :code)]

我认为这是最优的,因为您不必加载一堆国家/地区对象并迭代它们

Rails 3上的pluck方法不允许多个属性,但您可以执行以下操作:

 country_codes = Hash[Country.connection.select_rows(Country.select('name, code').to_sql)]

Answer 3

定义国家/地区哈希然后从您的记录中填充它.

countries_hash = {}
countries.each do |c|
  countries_hash[c.name] = c.code
end

Answer 4

这些天我最喜欢的答案是使用pluck和to_h

countries.pluck(:name, :code).to_h
# => {"United Sates" => "us", "United Kingdom" => "uk" .....}

反转它们并首先获得代码

countries.pluck(:code, :name).to_h
# => {"us" => "United Sates", "uk" => "United Kingdom" .....}