Question: rendering raw JSON

[disbelief]

So this might be too unusual a use case, but I have some pre-rendered JSON stored in memory already and I'd like to include it in my Jbuilder templates without needing to deserialize it first. Seems silly to deserialize JSON just to pass it to Jbuilder for serialization again.

What I'm doing now:

hash = JSON.parse(raw_json_string)
json.some_key hash

Ideally I'd like to do something like:

json.raw! :some_key, raw_json_string

Is this silly?

[rwz]

You could implement this feature like this:

# config/initializers/jbuilder_raw.rb

require "jbuilder"

class Jbuilder
  def set_raw!(attribute_name, json_string)
    set! attribute_name, MultiJson.load(json_string)
  end
end

And in your views use like this:

json.set_raw! :foo, bar

[disbelief]

Thanks for the reply, however this is essentially just moving what I was already doing down to the Jbuilder layer

I'm trying to avoid having to deserialize the JSON string entirely. Since Jbuilder just serializes it back into JSON after it's passed in as a Ruby hash. Ideally the set_raw! method would inject the raw JSON string into its final JSON output.

The conversion: JSON string -> Ruby Hash -> JSON String seems redundant to me, and slows performance if the JSON String is large/complex.

[rwz]

Jbuilder is doing MultiJson.dump(attributes_object) as the final step. There is no conventional way to inject raw json into serialiation process.

[disbelief]

Ah okay thanks @rwz! Wanted to see how feasible a set_raw! method would be. Sounds like it would require more modifications to Jbuilder than I'd like so I'll consider something else.

Out of curiosity, how does the cache! method work? If there's a cache hit, does the cached JSON also get deserialized by MulitJson before being dumped back into JSON?

[rwz]

cache! caches hash structure that later gets merged into the result before passing to MultiJson.dump.

As far as I know, partial injection of JSON is not yet implemented anywhere.

[disbelief]

I see, thanks again @rwz!

I might try to use the cache mechanism instead of a raw json string then. Sounds like there's still some serialization/deserialization that takes place, but performance might be better.

[shaokun]

It would be useful to support partial injection of JSON in some case. For example, extremely high performance are required.
After some googleing, I found that I could do something like:

require 'oj'

class CompiledJson
  def initialize(s); @s = s; end
  def to_json(*args); @s; end
  def to_s; @s; end

  undef_method :as_json
end

Oj.default_options = {:mode => :compat, use_to_json: true}

result = Jbuilder.new do |json|
  json.a CompiledJson.new('{x: "y"}')
end

puts result.target!
# => {"a": {x: "y"}}

[rwz]

@shaokun it's already there and works since forever.

class CompiledJson
  def initialize(s); @s = s; end
  def to_json(*); @s; end
end

Jbuilder.encode do |json|
  json.thing CompiledJson.new("foobar")
end # => "{\"thing\":foobar}"

[disbelief]

@rwz @shaokun thanks! This is actually exactly what I was looking for originally.

[shaokun]

@rwz The example you given doesn't work in a newly created rails 4.1.4 project. But it seems to work in rails 4.0.x. It returns # => "{"thing":{"s":"foobar"}}"

I am using oj and I followed the instruction here: ohler55/oj#140
It's something related to as_json and that's why I undefine that method.

I am also wondering it's possible to provide some API in jbuilder to support this cached json string? Something similar to the cache! API. It's difficult when I think about it, because the jbuilder is based on hash and array merging, so given an string, we will need to manually specify a key for it.

[rwz]

Well, that is actually because active support changed the way it handles json since 4.1. And because it defines to_json/as_json behavior for all classes, there is practically no way around it that doesn't involve modifying its internals.

So, here's the code I ended up with having a very similar problem: https://gist.github.com/rwz/14c0d8a5187b69922bb4

[waissbluth]

Thank you @rwz that was really helpful. I wonder if support for this could be added to jbuilder though.

[skensell]

Any chance jbuilder will support raw JSON in the near future? My use case is that I'm doing a postgres database query using the aggregate function 'json_agg' which conveniently returns the needed raw json. It would be great if I could just inject it into my jbuilder templates. I guess for now I'll go with the gist @RWS provided, thanks!