scope的用法

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scope可以将查询条件整合起来，让程序简洁易懂。并且可以串接使用。

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class Event < ActiveRecord::Base
    scope :open_public, -> { where( :is_public => true ) }
    scope :recent_three_days, -> { where(["created_at > ? ", Time.now - 3.days ]) }
end
调用
Event.open_public
Event.open_public.recent_three_days

预设的scope

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class Event < ActiveRecord::Base
    default_scope -> { order('id DESC') }
end

暂时取消预设的scope

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Event.unscoped do
    Event.all
    # SELECT * FROM events
end

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class Event < ActiveRecord::Base
    scope :recent, ->(date) { where("created_at > ?", date) }
    # 等同於 scope :recent, lambda{ |date| where(["created_at > ? ", date ]) }
    # 或 scope :recent, Proc.new{ |t| where(["created_at > ? ", t ]) }
end
Event.recent( Time.now - 7.days )