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

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

而连接表迁移是：

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

我正在尝试根据城市 ID 查找公司：

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: 缺少表“city”的 FROM 子句条目 第 1 行：...cities"."id" = "cities_companies"."city_id" WHERE "city"."id...^ : SELECT "companies"."id" AS t0_r0, "companies"."name" AS t0_r1, "公司"."category_id" AS t0_r2, "公司"."url" AS t0_r3, "公司"."created_at" AS t0_r4, "公司"."updated_at" AS t0_r5, "公司"."image_file_name" AS t0_r6, "公司"."image_content_type" AS t0_r7, "公司"."image_file_size" AS t0_r8, "公司"."image_updated_at" AS t0_r9, "cities"."id" AS t1_r0, "cities"."name" AS t1_r1, "城市"."state_id" AS t1_r2, "城市"."created_at" AS t1_r3, "cities"."updated_at" AS t1_r4 FROM "companies" 左外连接 "cities_companies" ON "cities_companies"."company_id" = "companies"."id" LEFT OUTER JOIN "cities" ON "cities"."id" = "cities_companies"."city_id" WHERE "city"."id" = '14'

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

Answer 1

问题出在您的where 子句中。

当表名应该是 cities.id 时，您正在引用 city.id。

一个更好的写法是使用散列语法

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