Ruby on Rails JSON.parse(object.to_json) doesn't return the original object

Question

It seems that with an object like this:

#<Course id: 1, name: "Targeting Triple Negative Breast Cancer", description: nil, disclosure: nil, created_at: "2010-11-11 14:43:31", updated_at: "2010-11-11 14:43:31", picture: nil, course_reference_id: nil, authors: "Lisa A. Carey, M.D.", volumn_number: nil, publication_date: nil, expiration_date: nil, credits: 1, featured: false>

I should be able to do JSON.parse(course.to_json), but when I try this, instead of returning the original object, I get the equivalent of Course.new (an object with nil attributes).

When I do course.to_json I get:

"{\"attributes\":{\"name\":\"Targeting Triple Negative Breast Cancer\",\"expiration_date\":null,\"created_at\":\"2010-11-11 14:43:31\",\"featured\":\"0\",\"publication_date\":null,\"updated_at\":\"2010-11-11 14:43:31\",\"id\":\"1\",\"disclosure\":null,\"volumn_number\":null,\"credits\":\"1\",\"authors\":\"Lisa A. Carey, M.D.\",\"course_reference_id\":null,\"description\":null,\"picture\":null},\"json_class\":\"Course\",\"attributes_cache\":{}}"

But when I do JSON.parse(course.to_json) I get:

#<Course id: nil, name: nil, description: nil, disclosure: nil, created_at: nil, updated_at: nil, picture: nil, course_reference_id: nil, authors: nil, volumn_number: nil, publication_date: nil, expiration_date: nil, credits: nil, featured: false>

I am using Rails 2.3.5 and I get the same result with other objects.

Simone Carletti · Accepted Answer · 2011-01-17 15:08:29Z

3

To serialize/deserialize the object use #to_json and #from_json. Don't try to parse the JSON string directly.

json = Course.new(...).to_json
Course.new.from_json(json)

Also note you should avoid calling JSON.parse directly. Use ActiveSupport::JSON bridge instead.

edited Jan 17, 2011 at 15:08

answered Nov 15, 2010 at 19:22

Simone Carletti

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1 Comment

Reed G. Law Over a year ago

When I try that I get ActiveRecord::UnknownAttributeError: unknown attribute: json_class

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