嵌套的 ActiveRecord 访问答案

【问题标题】：Nested ActiveRecord access嵌套的 ActiveRecord 访问
【发布时间】：2018-01-15 16:39:23
【问题描述】：

我正在尝试访问我的 Rails 项目中的嵌套 ActiveRecord 数据。
我想访问单个用户的所有子网中的所有设备
我想做这样的事情：

def index
    @user = User.find(params[:user_id])
    @subnets = @user.subnets.all
    @devices = @subnets.each.devices.order(sort_column+' '+sort_direction).search(params[:search])
    respond_to do |format|
      format.html
      format.csv { send_data Device.to_csv(@devices) }
    end
end

但是@subnet.each.devices 部分不起作用。

有没有一种方法可以在不迭代和创建数组的情况下做到这一点，从那以后我就不能再使用 order 函数了。

【问题讨论】：

标签： ruby-on-rails ruby ruby-on-rails-3 activerecord

【解决方案1】：

尝试使用joins

@devices = Device.joins(:subnets).where('subnets.user_id = :id', id: @user.id)

【讨论】：

页面加载，我看到了我需要的所有子网，但是一旦我尝试搜索，我得到这个 SQL 错误：SQLite3::SQLException: ambiguous column name: name: SELECT "devices".* FROM "devices" INNER JOIN "subnets" ON "subnets"."id" = "devices"."subnet_id" WHERE (subnets.user_id = 4) AND (name LIKE '%TEST%' OR IP LIKE '%TEST%' OR MAC LIKE '%TEST%') ORDER BY IP asc
我发现了我的错误：D 我的搜索例程使用了... name LIKE ...，但子网和设备确实有名称。所以我把它改成了... devices.name LIKE ...，现在它可以工作了；）

【解决方案2】：

试试这个 eager_load

 u = User.eager_load({subnets: :devices}).order('devices.updated_by desc').find(1)

这是我日志中的查询

SELECT "users"."id" AS t0_r0, "users"."username" AS t0_r1, "users"."created_at" AS t0_r2, "users"."updated_at" AS t0_r3, "users"."company_id" AS t0_r4, "users"."location_id" AS t0_r5, "subnets"."id" AS t1_r0, "subnets"."user_id" AS t1_r1, "devices"."id" AS t2_r0, "devices"."subnets_id" AS t2_r1, "devices"."updated_by" AS t2_r2, "devices"."created_by" AS t2_r3 FROM "users" LEFT OUTER JOIN "subnets" ON "subnets"."user_id" = "users"."id" LEFT OUTER JOIN "devices" ON "devices"."subnets_id" = "subnets"."id" WHERE "users"."id" = ? AND "users"."id" = 1 ORDER BY devices.updated_by desc

在此之后，您可以轻松获得设备 :)

【讨论】：