additional model attributes

rubyonrails-talk
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

2

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.

foo.to_json(:methods => [:attr1, :attr2]) Maybe? (assuming that foo.attr1 returns one of your extra attributes)

Fred.

3

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

4

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.

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

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

7

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

8

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