2

Probably a stupid question but I'm relatively new to Rails and wondering how Rails handles serializing a model that has_many (and/or belongs_to) objects of another class. Will it serialize the whole object graph by default? Do you, necessarily, want that? Can you control it? How?

Any tricks on the receiving end regarding how to de-serialize it? or pretty much brute force assign properties to their hash value and any embedded arrays/hashes would then become associated class objects?

Edit: Adding example of json returned using @zetetic's example. Wondering why embedded collection (grommets) have escape(\) characters before each quote(")?

{"name":"Gizmo","height":15,"grommets":"[{\"name\":\"Sid\",\"color\":\"yellow\"},{\"name\":\"Elvis\",\"color\":\"\"},{\"name\":\"Teeny\",\"color\":\"Red\"}
Meltemi
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2 Answers2

3

No, by default serializing a model instance emits only its own attributes, not those of its associations. But you can customize this behavior by including an as_json method in the model:

class MyModel < ActiveRecord::Base
  has_many :widgets

  def as_json(options={})
    {
      :name => name,
      :widgets => widgets.to_json
    }
  end
end

You'll probably want to define as_json in the associated model also, or else you get the standard hash of attributes.

EDIT

Turns out the example above works only for the top level, not for the associations, which end up escaped. To get the example working, define as_json with the desired attributes in Widget, then in MyModel call as_json on each element of the collection :

def as_json(options={})
  {
    :name => name,
    :widgets => widgets.map(&:as_json)
  }
end

I guess you could monkeypatch Array#as_json instead, though I prefer using map.

EDIT

If you are thinking of upvoting this answer, be sure to read this one first. Using :include is the preferred approach.

Community
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zetetic
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  • thanks! it's *mostly* working. any idea why when I add `as_json(options={})` and only :name => name each element of the referenced `:widgets` (using your example) is 'escaped' with backslash(`\`) characters before each quote(`"`). But this isn't the case for elements in `MyModel`. see example after my original question. – Meltemi Dec 03 '10 at 07:36
  • FYI - I started a new post to get an answer to the **backslash escape** issue: http://stackoverflow.com/questions/4348223 – Meltemi Dec 03 '10 at 18:40
1

Easy! (tested on Rails 2.3.8)

from http://apidock.com/rails/ActiveRecord/Serialization/to_json

To include associations, use :include

    konata.to_json(:include => :posts)
  # => {"id": 1, "name": "Konata Izumi", "age": 16,
        "created_at": "2006/08/01", "awesome": true,
        "posts": [{"id": 1, "author_id": 1, "title": "Welcome to the weblog"},
                  {"id": 2, author_id: 1, "title": "So I was thinking"}]}

See link above for more.

For me, it even worked with ":has_many, :through" associations.

FernandoFabreti
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  • Can anyone verify that this is the preferred method (or at least works) with with Rails 3? The documentation you link to is missing for Rails 3... – Meltemi Dec 30 '10 at 18:45