include 和 where 没有检索到正确关联的对象答案

【问题标题】：The includes and where doesn't retrieve the correctly associated objectinclude 和 where 没有检索到正确关联的对象
【发布时间】：2014-06-27 19:30:58
【问题描述】：

我正在尝试在我的项目中实现搜索功能，所以我添加了类方法：

    class Donation < ActiveRecord::Base
      belongs_to :member
      def self.search_by_name name
        includes(:member).where(member:  { name: name } )
      end
    end

我在 donatinos#index 中调用它

    class DonationsController < ApplicationController
      def index
        search_donations
      end

      private
      def search_donations
        if !params[:name].blank?
          @donations = Donation.search_by_name params[:name]
        else
          @donations = Donation.all
        end
      end    
    end

最后，我实现了索引模板：

    <%= form_tag donations_path,:method => 'get' do %>
        <%= text_field_tag :name %>
        <%= submit_tag "search", name: nil %>
    <% end %>
    <table>
        <% @donations.each do |donation| %>
        <tr>
            <td><%= donation.total %></td>
        </tr>
        <% end %>
        </tbody>
    </table>

我在表格中输入“Ted Wang”后收到错误消息

    SQLite3::SQLException: no such column: member.name: SELECT "donations"."id" AS t0_r0, "donations"."organization_id" AS t0_r1, "donations"."category" AS t0_r2, "donations"."borrow_id" AS t0_r3, "donations"."member_id" AS t0_r4, "donations"."total" AS t0_r5, "donations"."note" AS t0_r6, "donations"."created_at" AS t0_r7, "donations"."updated_at" AS t0_r8, "donations"."time" AS t0_r9, "members"."id" AS t1_r0, "members"."no" AS t1_r1, "members"."name" AS t1_r2, "members"."nick_name" AS t1_r3, "members"."introducer" AS t1_r4, "members"."role" AS t1_r5, "members"."gender" AS t1_r6, "members"."birthday" AS t1_r7, "members"."lunar_birthday" AS t1_r8, "members"."lunar_deathday" AS t1_r9, "members"."identified_number" AS t1_r10, "members"."home_phone" AS t1_r11, "members"."company_phone" AS t1_r12, "members"."bbcall" AS t1_r13, "members"."mobile" AS t1_r14, "members"."address" AS t1_r15, "members"."permanent_address" AS t1_r16, "members"."education" AS t1_r17, "members"."job" AS t1_r18, "members"."created_at" AS t1_r19, "members"."updated_at" AS t1_r20, "members"."organization_type" AS t1_r21, "members"."organization_id" AS t1_r22, "members"."involved" AS t1_r23 FROM "donations" LEFT OUTER JOIN "members" ON "members"."id" = "donations"."member_id" WHERE "member"."name" = 'Ted Wang'

我用错了includes吗？并且成员具有属性名称，我也运行了 db:migrate。

【问题讨论】：

免去重新发明轮子的痛苦，然后看到有更好的预制件，比如 Ransack => ruby-toolbox.com/categories/Active_Record_Named_Scopes

标签： sql ruby-on-rails ruby rails-activerecord

【解决方案1】：

根据 Rails 约定，表名是小写和复数的模型名称，因此在 where 子句中您应该指定 members（在 plural 中）而不是 member（在 singular ）。

您可以通过查看错误消息轻松调试此问题：SQLite3::SQLException: no such column: member.name。通过错误消息，可以诊断出表名是members，因此查询中的某些内容肯定是错误的，因为它引用了member.name 而不是members.name。

def self.search_by_name name
  includes(:member).where(members: { name: name } )
  ##                       ^
  ##                       plural
end

【讨论】：

有效！非常感谢！我忘记了 where() 是在表上指定的，不像 `donation.member.where(name: name)。

【解决方案2】：

 def self.search_by_name name
    includes(:member).where("members.name = ?", name)
 end

其他一切都保持不变。

【讨论】：

【解决方案3】：

您可以使用范围（这通常是通过 rails 中的方法指定查询的标准方式）

scope :filter_by_member_name, lambda { |name| select("*").where("donations d, members m").where("d.member_id= m.id").where("m.name LIKE ?",  "%#{value}%") if name }

然后在你的控制器中

@donations = Donation.filter_by_member_name(params[:name])

通过手动加入会员和捐赠，您不需要活动记录来启动两个查询并将所有内容拼凑在一起。
只需替换 select() 中的参数即可。

【讨论】：