ActiveRecord Sum Max Joins 结果数组中有多个 nil id

Question

与Rails activerecord : sum, max and joins

相同的问题

除了得到奇怪的结果。

class CustomResumeline < ActiveRecord::Base
  has_many :resumeline_words
end

class ResumelineWord < ActiveRecord::Base
  belongs_to :custom_resumeline
end

CustomResumeline.joins(:resumeline_words).where(resumeline_words: {name: ["time", "data"]}).select('sum(resumeline_words.weight) as nb_votes').group('resumeline_words.custom_resumeline_id').order('nb_votes ASC')

结果

CustomResumeline Load (0.8ms)  SELECT sum(resumeline_words.weight) as nb_votes FROM "custom_resumelines" INNER JOIN "resumeline_words" ON "resumeline_words"."custom_resumeline_id" = "custom_resumelines"."id" WHERE "resumeline_words"."name" IN ('time', 'data') GROUP BY resumeline_words.custom_resumeline_id  ORDER BY nb_votes ASC
 => #<ActiveRecord::Relation [#<CustomResumeline id: nil>, #<CustomResumeline id: nil>, #<CustomResumeline id: nil>, #<CustomResumeline id: nil>, #<CustomResumeline id: nil>, #<CustomResumeline id: nil>, #<CustomResumeline id: nil>, #<CustomResumeline id: nil>, #<CustomResumeline id: nil>, #<CustomResumeline id: nil>, ...]>

我的问题是，为什么我会得到一个包含一堆 nil id CustomResumelines 的数组？

谢谢

Answer 1

根据您的查询，您正在使用 #select 到

result =  CustomResumeline.joins(:resumeline_words)...

result returns 一个 relation 对象，其中 id 将由 Rails 添加，因为您使用 #select，虽然你还没有选择它。你现在可以做

result. map { |rec| rec.nb_votes }
# will give array of `nb_votes` values.

Selecting Specific Fields 指南中的一些提示：

Client.select("viewable_by, locked") - to select only viewable_by and locked columns. Be careful because this also means you're initializing a model object with only the fields that you've selected. If you attempt to access a field that is not in the initialized record you'll receive: ActiveModel::MissingAttributeError: missing attribute: <attribute>. Where <attribute> is the attribute you asked for. The id method will not raise the ActiveRecord::MissingAttributeError, so just be careful when working with associations because they need the id method to function properly.

所以 id 方法不会引发 ActiveRecord::MissingAttributeError,.. - 为什么？ As #select 默认情况下将它添加到它创建的每个模型对象中，其值为 id as nil.

ActiveRecord Sum Max Joins 结果数组中有多个 nil id

ActiveRecord Sum Max Joins results in array with multiple nil ids

activerecord

join

sum

ruby-on-rails