Ruby-on-rails PG::UndefinedTable：错误：在使用连接和 where 时缺少表的 FROM 子句条目
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PG::UndefinedTable: ERROR: missing FROM-clause entry for table when using joins and where
提问by Huy
I have two models, Courierand Order.
我有两个模型，Courier和Order.
I have the following query below:
我有以下查询：
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).
此查询有效，但是，它会提取所有订单。我想将订单限制为当天的订单。所以我添加了以下查询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:
这给了我错误：
PG::UndefinedTable: ERROR: missing FROM-clause entry for table "orders"
What am I doing incorrectly here?
我在这里做错了什么？
回答by Dane O'Connor
Hmm it looks like you're trying to include current_ordersand 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 referencesmethod when referencing a joined table. Perhaps, try something like this:
嗯，看起来您正在尝试包含current_orders和包含order. 这些是不同条件的相同表吗？这可能会混淆活动记录。另外，我很确定references在引用连接表时包含该方法是明智的。也许，尝试这样的事情：
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by mattcongel
You can also use eager_loadto provide the same exact behavior as includes+ referencesdoes. It performs the same Left Outer Join on the table passed as an argument, but in a much cleaner manner.
您还可以使用eager_load来提供与includes+完全相同的行为references。它对作为参数传递的表执行相同的左外连接，但方式更简洁。
Docs here: http://apidock.com/rails/v4.2.7/ActiveRecord/QueryMethods/eager_load
文档在这里：http: //apidock.com/rails/v4.2.7/ActiveRecord/QueryMethods/eager_load
Per this example:
根据这个例子：
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by Kiryl Plyashkevich
Make sure to provide .includes(:service_region)before filtering with where.
确保.includes(:service_region)在过滤前提供where.
