Deserialize ActiveRecord from JSON

Question

I would like to save query result into redis using JSON serialization and query it back.

Getting query results to json is pretty easy:

JSON.generate(Model.all.collect {|item| item.attributes})

However I did not find a proper way to deserialize it back to ActiveRecord. The most straight-forward way:

JSON.parse(@json_string).collect {|item| Model.new.from_json(item)}

Gives me an error:

WARNING: Can't mass-assign protected attributes: id

So id gets empty. I thought of just using OpenStruct for the views instead of ActiveRecord but I am sure there is a better way.

Leitao

Answer 1

You could instantiate the new object from JSON and then assign the id afterwards. Probably best to create your own method for this:

class Model
  def self.from_json_with_id(params = {})
    params = JSON.parse(params)
    model = new(params.reject {|k,v| k == "id"})
    model.id = params["id"]
    model
  end
end

Or maybe just override the from_json() method.

Positronium

Though I am suprised there is no built in support for this. This sounds good. Thanks – Leitao

Just a heads up, I was winging this. You might want to use allocate instead of new if you want ActiveRecord to realize it's not a new object in the database – Positronium

Answer 2

Why not like this:

JSON.parse(@json_string).each do |item|
     item.delete(:id) # I tested it in my case it also works without this line
     object=Model.create(item)
end

If the host that created the JSON adds a JSON root you might have to use item[1] instead of item.

Toadstool

The json items came from the database in the first place. Using model.create will attempt to create the item in the database and will fail since the item already exists. – Leitao