Rails的范围，什么也不做对未在值 [英] Rails scope that does nothing for NOT IN values

问题描述

我有一个Rails 3的范围排除ID数组。

I have a Rails 3 scope that excludes an array of ids.

什么是如此，它什么都不做，当数组是空的，仍然可链接写入范围的最佳方法是什么？我现在有这个，它的工作原理，但似乎有点做作：

What is the best way to write the scope so that it does nothing when the array is empty and is still chainable? I currently have this, which works, but seems a little hokey:

scope :excluding_ids, 
         lambda {|ids| ids.empty? ? relation : where('id not in (?)', ids) }

如果我没有ids.empty关系：？？位，当id为空，生成的SQL是

If I do not have the "ids.empty? ? relation :" bit, when ids is empty the SQL generated is

... ID not in (NULL) ...

这将不可能有返回结果。所以是这样的：

which will always return nothing. So something like:

Model.excluding_ids([]).where('id > 0')

不返回任何结果。

returns no results.

推荐答案

如果在 IDS 数组为空，那么不返回任何东西。

If the ids array is empty then don't return anything.

scope :excluding_ids, lambda { |ids|
  where(['id NOT IN (?)', ids]) if ids.any?
}

查询将在查询运行，没有任何额外的限制，如果没有 IDS 。

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