Question

I have send json response of a Rails AREL query result based on two tables. The response includes two timestamp columns: updated_at and updated_at_table_2. I override ActiveSupport::TimeWithZone.as_json method to obtain the desired datetime format for JSON. The same approach is shown at

http://stackoverflow.com/questions/2937740/rails-dates-with-json

My current JSON response is:
{
“updated_at”:”10/26/2012 22:04:07 -0400″,
“updated_at_table_2″:”2012-10-27 02:04:07.463015”
}

I want them to be the same. I relies below Rails code to produce json.

render :json => { :customer_order  =>  @customer_order  }

where @custoemr_order derived from:

CustomerOrder.select(%Q[
      updated_at,
      c.updated_at as updated_at_table_2
    ] ).
    joins( %{ as co inner join customers as c on (co.customer_id = c.id)

Question: how can I tell Rails 3 to process as_json the same way for updated_at_table_2 as for updated_at column?

Any suggestions/pointers are great too.

Note: I found this post asking about the same root problem (though not about json) without good solution. :

http://stackoverflow.com/questions/12067173/rails-postgres-not-returning-timezone-info-on-column-from-joined-table

Answer 1

If you look at what your query gives you, you’ll see exactly where you’re going wrong:

 > o = CustomerOrder.select(%Q[ ... ]).joins(...)
 > puts o.updated_at.class
=> ActiveSupport::TimeWithZone
 > puts o.updated_at_table_2.class
=> String

ActiveRecord has no way of know what sort of thing updated_at_table_2 is supposed to be so it leaves it as a String and your to_json monkey patch won’t be applied to strings.

If you want to keep using your to_json monkey patch (which I think is a bad idea), then you need to manually convert updated_at_table_2 to an ActiveSupport::TimeWithZone with something like this:

x = ActiveSupport::TimeWithZone.new(
    Time.parse(o.updated_at_table_2),
    Time.zone
)
# x is now an ActiveSupport::TimeWithZone

Alternatively, you could load the associated object and call updated_at on that.

I’d scrap the whole approach though: let the server work exclusively in UTC, send the clients timestamps in an ISO-8601 format, and let the clients deal with applying the local timezone.