PG::UndefinedTable: ERROR: missing FROM-clause entry for table when using joins and where

问题

I have two models, Courier and Order.

I have the following query below:

active_couriers = Courier.
  available_courier_status.
  where(:service_region_id => @service_region.id).
  includes(:orders)

This query works, however, it pulls in all orders. I want to limit the orders to only orders for the day. So I added the following query where("orders.created_at >= ?", Time.zone.now.beginning_of_day).

active_couriers = Courier.
  available_courier_status.
  where(:service_region_id => @service_region.id).
  includes(:current_orders).
  includes(:orders).
  where("orders.created_at >= ?", Time.zone.now.beginning_of_day)

This give me the error:

PG::UndefinedTable: ERROR:  missing FROM-clause entry for table "orders"

What am I doing incorrectly here?

回答1:

Hmm it looks like you're trying to include current_orders and include order. Are these the same tables with different conditions? This might be confuse active record. Also, I'm pretty sure it's wise to include the references method when referencing a joined table. Perhaps, try something like this:

active_couriers = Courier.includes(:orders)
  .available_courier_status
  .where(:service_region_id => @service_region.id)
  .where("orders.created_at >= ?", Time.zone.now.beginning_of_day)
  .references(:orders)

回答2:

You can also use eager_load to provide the same exact behavior as includes + references does. It performs the same Left Outer Join on the table passed as an argument, but in a much cleaner manner.

Docs here: http://apidock.com/rails/v4.2.7/ActiveRecord/QueryMethods/eager_load

Per this example:

active_couriers = Courier.eager_load(:orders)
  .available_courier_status
  .where(:service_region_id => @service_region.id)
  .where("orders.created_at >= ?", Time.zone.now.beginning_of_day)

回答3:

Make sure to provide .includes(:service_region) before filtering with where.

来源：https://stackoverflow.com/questions/25099668/pgundefinedtable-error-missing-from-clause-entry-for-table-when-using-joins