How can I use a named scope in my model against an array of items?

Question

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}}}

Answer 1

In Rails 4, I can check for the inclusion of a string in an array attribute by using a scope like this:

scope :news, -> { where(:categories => '{news}') }

Or with an argument:

scope :by_category, ->(category) { where(:categories => "{#{category}}") }