Average number of days since a date in postgresql/rails -

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i want calculate average number of days since 'date_from' (it varies)

user.all.average('? - date_from', time.now.to_date)

gives error

undefined method `except' thu, 27 nov 2014:date

see ruby_on_rails/activerecord/calculations

the second parameter of average options(an hash)

the options can used customize query :conditions, :order, :group, :having , :joins.

so should generate average expression this:

user.average("'#{time.now.to_date}' - date_from" )

then rails generate sql this:

select avg('2014-11-27' - date_from) avg_id ...

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