如何在模型中对项目数组使用命名作用域? [英] How can I use a named scope in my model against an array of items?

问题描述

我知道我可以像这样在数组中查询最近的书

I know that I can do a query for recent books based on an array as in

scope :recent_books, lambda {|since_dt| {:conditions=>{:created_at >= since_dt}}}

但是当我有一系列项目(例如，如果我想知道是否有与[date1，date2，date3等]数组中的日期匹配的记录，怎么办?

but how can I do a similar query when I have an array of items, e.g. what if I want to know if there any records that match the dates in an array of [date1, date2, date3, etc.]

我认为必须有一个收集/注入/选择/映射方法，但我不确定从阅读它们中会得到什么.

I think there must be a collect/inject/select/map y method that'll do it but I am not sure which from reading them.

推荐答案

如果将数组作为值传递，则ActiveRecord足够聪明以进行比较以包含在数组中.例如，

If you pass an array as the value, ActiveRecord is smart enough to compare for inclusion in the array. For example,

Book.where(:author_id => [1, 7, 42])

生成带有WHERE子句的SQL查询，类似于:

produces a SQL query with a WHERE clause similar to:

WHERE "author_id" IN (1, 7, 42)

您可以像设置正常条件一样，以scope的方式利用此优势:

You can take advantage of this in a scope the same way you would set normal conditions:

class Book < ....
  # Rails 3
  scope :by_author, lambda { |author_id| where(:author_id => author_id) }

  # Rails 2
  named_scope :by_author, lambda { |author_id
    { :conditions => {:author_id => author_id} }
  }
end

然后，您可以将单个ID或ID数组传递给by_author，它将正常工作:

Then you can pass a single ID or an array of IDs to by_author and it will just work:

Book.by_author([1,7,42])

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