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我有以下命名范围

  class RentableItem < ActiveRecord::Base
  named_scope :available_at, lambda{ |starts_at, ends_at| { 
      :select => "t.*",
      :from => "(SELECT ri.*, COALESCE(c1.start_date, '#{starts_at}') AS EarliestAvailable,
                              COALESCE(c2.end_date, '#{ends_at}') AS LatestAvailable
                FROM rentable_items ri
                LEFT OUTER JOIN contracts c1 ON (ri.id = c1.rentable_item_id AND c1.start_date BETWEEN '#{starts_at}' AND '#{ends_at}')
                LEFT OUTER JOIN contracts c2 ON (ri.id = c2.rentable_item_id AND c2.end_date BETWEEN '#{starts_at}'
                AND '#{ends_at}' AND c2.start_date >= c1.end_date))
                AS t",
      :joins =>"LEFT OUTER JOIN contracts x ON (t.id = x.rentable_item_id AND x.start_date < t.LatestAvailable
                AND x.end_date > t.EarliestAvailable)",
      :conditions => "x.id IS NULL AND DATEDIFF(t.LatestAvailable, t.EarliestAvailable) >= #{(starts_at.to_date..ends_at.to_date).to_a.size - 1}"
      }}
end

对这个 named_scope 的单个调用就像一个魅力，但是当我试图将几个命名范围链接在一起，或者通过一个关联范围访问这个 named_scope 时，它​​会爆炸。我认为，select 语句和自定义 from 子句是问题所在。也许有人知道如何重写这个 named_scope 以允许链接和限定槽关联？

编辑：

多亏了 Shtéf，它正在工作。

  named_scope :available_at, lambda{ |starts_at, ends_at| { 
      :select => "rentable_items.*",
      :from => "(SELECT ri.*, COALESCE(c1.start_date, '#{starts_at}') AS EarliestAvailable,
                              COALESCE(c2.end_date, '#{ends_at}') AS LatestAvailable
                FROM rentable_items ri
                LEFT OUTER JOIN contracts c1 ON (ri.id = c1.rentable_item_id AND c1.start_date BETWEEN '#{starts_at}' AND '#{ends_at}')
                LEFT OUTER JOIN contracts c2 ON (ri.id = c2.rentable_item_id AND c2.end_date BETWEEN '#{starts_at}'
 AND '#{ends_at}' AND c2.start_date >= c1.end_date))
 AS rentable_items",
      :joins =>"LEFT OUTER JOIN contracts x ON (rentable_items.id = x.rentable_item_id AND x.start_date < rentable_items.LatestAvailable
AND x.end_date > rentable_items.EarliestAvailable)",
      :conditions => "x.id IS NULL AND DATEDIFF(rentable_items.LatestAvailable, rentable_items.EarliestAvailable) >= #{(starts_at.to_date..ends_at.to_date).to_a.size - 1}"
      }}

这使我现在可以链接范围并通过关联访问它。

轨道生成的双重 where 条件可能只是一个装饰性的小问题（在开始和结束时：

WHERE (`rentable_items`.container_item_id = 1) AND (((size > 10) AND (x.id IS NULL AND DATEDIFF(rentable_items.LatestAvailable, rentable_items.EarliestAvailable) >= 28)) AND (`rentable_items`.container_item_id = 1))
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1 回答 1

0

您应该检查应用程序的日志文件，并查看 Rails 所做的哪些假设导致生成的查询失败。如果您无法修复它，请向我们展示您尝试通过它访问它的示例关联，以及 Rails 从日志文件生成的查询。

我的直觉是，Rails 假设它可以像访问表rentable_items一样访问该表rentable_items，但是相反，您ri在这种情况下已经给它起了别名。

于 2010-02-07T20:28:29.857 回答