ActiveRecord的总和最大联接结果阵列与多个零IDS [英] ActiveRecord Sum Max Joins results in array with multiple nil ids

问题描述

同样的问题 Rails的ActiveRecord的：总和，最大值和加入

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，为什么我得到一个数组有一堆零号CustomResumelines？

My question is, why am I getting an array with a bunch of nil id CustomResumelines ?

感谢

推荐答案

根据您的查询，使用＃选择到

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

结果返回相关的对象，其中 ID 将Rails的添加为你使用＃选择，虽然你没有选择它。现在，您可以做

result returns a relation object, where id will added by Rails as you used #select, although you have not selected it. You can do now

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

从一些提示选择具体领域指南：

Client.select（viewable_by，锁定） - 只选择viewable_by和锁定列。要小心，因为这也意味着你的初始化 模型对象的只有你所选择的领域。如果您试图访问一个字段是不是在初始化的记录，您将获得：加载ActiveModel :: MissingAttributeError：缺少属性：其中;属性＆GT; 。其中，＆LT;属性＆GT; 是你要的属性。该 ID 方法不会提高的ActiveRecord :: MissingAttributeError ，所以用的协会工作时，只是要小心的，因为他们需要的ID的方法才能正常工作。

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.

所以的 ID 方法不会提高的ActiveRecord :: MissingAttributeError .. - 为什么？由于＃选择默认情况下，将其添加到通过将其与 ID 的值，生成每个模型对象零。

So The id method will not raise the ActiveRecord::MissingAttributeError,.. -- Why ? As #select add it by default it to each model object created by it with a value of id as nil.

这篇关于ActiveRecord的总和最大联接结果阵列与多个零IDS的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！