Question

所以，我有这两个模型：

class City < ActiveRecord::Base
  has_and_belongs_to_many :companies
end

class Company < ActiveRecord::Base
  has_and_belongs_to_many :cities
end

连接表迁移是：

class CreateJoinCityCompany < ActiveRecord::Migration    
  def up                                
    create_table :cities_companies do |t|                        
      t.integer :city_id                                                                    
      t.integer :company_id                                                                 
    end                                                                                     
  end                                                                                       

  def down                                                                                  
    drop_table :cities_companies                                                            
  end                                                                                       
end

我试图根据城市ID找到公司：

class CompaniesController < ApplicationController
  def index
      @companies = Company.includes(:cities).where('city.id' => params[:city_id]).references(:cities)
      render :text => @companies.inspect
  end
end

我得到的是：

PG :: UndefinedTable：错误：表＆＃34; city＆＃34;缺少FROM子句条目第1行：......城市＆＃34;。＆＃34; id＆＃34; =＆＃34; cities_companies＆＃34;。＆＃34; city_id＆＃34;哪里＆＃34; city＆＃34;。＆＃34; id ... ^：SELECT＆＃34;公司＆＃34;。＆＃34; id＆＃34; AS t0_r0，＆＃34;公司＆＃34;。＆＃34;名称＆＃34; AS t0_r1，＆＃34;公司＆＃34;。＆＃34; category_id＆＃34; AS t0_r2，＆＃34;公司＆＃34;。＆＃34; url＆＃34;如 t0_r3，＆＃34;公司＆＃34;。＆＃34; created_at＆＃34; AS t0_r4，＆＃34;公司＆＃34;。＆＃34; updated_at＆＃34;如 t0_r5，＆＃34;公司＆＃34;。＆＃34; image_file_name＆＃34; AS t0_r6，＃＆34;公司＆＃34;＆＃34; image_content_type＆＃34; AS t0_r7，＃＆34;公司＆＃34;＆＃34; IMAGE_FILE_SIZE＆＃34; AS t0_r8，＆＃34;公司＆＃34;。＆＃34; image_updated_at＆＃34; AS t0_r9，＆＃34; cities＆＃34;。＆＃34; id＆＃34; AS t1_r0，＆＃34; cities＆＃34;。＆＃34; name＆＃34; AS t1_r1，＆＃34;城市＆＃34;＆＃34; STATE_ID＆＃34; AS t1_r2，＆＃34; cities＆＃34;。＆＃34; created_at＆＃34; AS t1_r3，＃＆34;城市＆＃34;＆＃34;的updated_at＆＃34; AS t1_r4 FROM＆＃34;公司＆＃34; LEFT OUTER JOIN ＆＃34; cities_companies＆＃34; ON＆＃34; cities_companies＆＃34;。＆＃34; company_id＆＃34; = ＆＃34;公司＆＃34;＆＃34;编号＆＃34; LEFT OUTER JOIN＆＃34; cities＆＃34; ON＆＃34;城市＆＃34;。＆＃34; id＆＃34; = ＃＆34; cities_companies＆＃34;＆＃34; city_id＆＃34;在哪里＆＃34;城市＆＃34;。＆＃34; id＆＃34; =＆＃39; 14＆＃39;

我尝试了一些方法，比如将参数转换为int，但我需要一些帮助来弄清楚这里发生了什么。

Answer 1

问题出在你的where条款中。

您引用city.id时应该是cities.id，因为表名是城市。

更好的编写方法是使用哈希语法

Company.includes(:cities).where(cities: { id: params[:city_id] }).references(:cities)

rails：HABTM和ActiveRecord出错（PG :: UndefinedTable：ERROR：缺少FROM ...）

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