Automatically convert hash keys to camelCase in JBuilder

Question

I am using JBuilder version 2.4.1 and Rails 4.2.6. I am trying to serialize a complex object to JSON. The code looks as follows:

json.key_format! camelize: :lower

json.data_object @foo

@foo looks like this:

{
  key: 'value',
  long_key: 'value'
}

I expect it to be rendered as

{
  "dataObject": {
    "key": "value",
    "longKey": "value"
  }
}

But instead it keeps the original hash keys, only converting data_object into camelCase

{
  "dataObject": {
    "key": "value",
    "long_key": "value"
  }
}

So the question is: what is the proper way to camelize hash keys using JBuilder?

Answer 1

As Bryce has mentioned, Jbuilder uses to_json instead of processing the hash.

A simple solution is to use json.set! to manually serialize the hash.

json.key_format! camelize: :lower

json.data_object do
  @foo.each do |key, value|
    json.set! key, value
  end
end

Although, there is an issue: if @foo is empty, it won't create an object at all. These are the solutions I found:

1. Define an empty hash before the serialization

   json.key_format! camelize: :lower
   
   json.data_object({}) # don't forget parentheses or Ruby will handle {} as a block 
   
   json.data_object do
     @foo.each do |key, value|
       json.set! key, value
     end
   end
   

2. Serialize an empty hash if the source variable is empty

   json.key_format! camelize: :lower
   
   if (@foo.empty?) do 
     json.data_object({})
   else 
     json.data_object do
       @foo.each do |key, value|
         json.set! key, value
       end
     end
   end
   

   Or if you prefer your code flat

   json.key_format! camelize: :lower
   
   json.data_object({}) if @foo.empty?
   
   json.data_object do
     @foo.each do |key, value|
       json.set! key, value
     end
   end unless @foo.empty?
   

However, those solutions will not work if you have to serialize nested objects. You can achieve deep serialization by monkeypatching the json object inside Jbuilder

def json.hash!(name, hash)
  if hash.empty?
    set! name, {}
  else
    set! name do
      hash.each do |key, value|
        if value.is_a?(Hash)
          hash! key, value
        else
          set! key, value
        end
      end
    end
  end
end

Then you can simply use json.hash! :data_object, @foo and get the desired result.