Additional model attributes

Rails
#1

Hi,
i have a “place” model with 2 columns (id, name).
I’m calling an external api which gives me data to create a new place
object.

I would like to add the address from the external place to the place
object and render it as a json result, without storing it in the
database.

i don’t get any errors, but the address never shows up within the json
output. i’ve tried with attr_accessor but that didn’t work either.

any hints?

thanks

==========================================
place.rb

class Place < ActiveRecord::Base
attr_accessor: address
end

==========================================
places_controller.rb

external_api_place_data = @client.find(place_id)
place = Place.new
place.name = place.name
place.id = place.id

//not showing up in the json result
place.address = external_api_place_data.address

places = []
places << place

respond_to do |format|
format.html # index.html.erb
format.json { render json: places }
end

==========================================

#2

On 25 Oct 2011, at 14:03, “Lukas M.” [email protected] wrote:

output. i’ve tried with attr_accessor but that didn’t work either.
foo.to_json(:methods => [:attr1, :attr2])
Maybe? (assuming that foo.attr1 returns one of your extra attributes)

Fred.

#3

I think for Rails to recognize that the attribute should be included,
you
need to use attr_accessible rather than the Ruby method attr_accessor.

#4

hi,
that works but not in the case when i would like to do something like
this:

user_place = Location.new(:place => place, :user => user)

user_place.to_json //address is missing

#5

hm… no luck with that either. when i try to print out the places object
in the console (logger.debug @place.to_yaml), “address” is missing.

#6

On Tue, Oct 25, 2011 at 5:00 PM, Lukas M. [email protected] wrote:

hm… no luck with that either. when i try to print out the places object
in the console (logger.debug @place.to_yaml), “address” is missing.

From the top of my head (not hard tested now).

Now you refer to to_yaml, in previous mails, you refered to to_json.

Be careful, there is a fundamental difference between to_xml, to_json,
to_yaml on ActiveRecord …

One of them (I believe to_yaml) prints the “raw” database column values,
even if you overwrite that accessor function with a name. The other two
(to_json, to_xml IIRC) use the attribute accessors (from ActiveRecord I
presume), that can be overwritten by your own code.

So, I would expect to_yaml to never work in this scenario (where there
is
no database column). But to_json should be possible in this scenario
(I did some simple tests with ActiveModel and that seemed to work as
expected).

HTH,

Peter

#7

One alternative in terms of dynamically adding an attribute to a model
instance (without having to have pre-defined any attr_… in the
class):

…
place = Place.new
place.name = place.name
place.id = place.id
place[‘address’] = external_api_place_data.address
…

From then on, for that instance, you can call place.address, and it
will show up in place.to_json (since to_json is generated from
place.attributes, which now has a k/v for address in attributes).

Jeff

On Oct 25, 8:16am, Frederick C. [email protected]

#8

On 25 Oct 2011, at 16:00, “Lukas M.” [email protected] wrote:

hm… no luck with that either. when i try to print out the places object
in the console (logger.debug @place.to_yaml), “address” is missing.

For json at least you could override the as_json method to add the
attributes you want.

Fred