How to deserialize params received as JSON string in controller? - ruby-on-rails

Question

I am using Rails to write a controller receiving JSON as its params, and then testing it with an Rspec request spec.
controller:
class API::UserController < ApplicationController
def create
#user = User.new(user_params)
if #user.save
redirect_to #user
else
render json: { errors: #user.errors.full_messages }, status: :unprocessable_entity
end
private
def user_params
params.require(:user).permit(:username, :email, :name, :password_digest)
end
end
spec:
RSpec.describe "User creation", type: :request do
def create_user_request
params = { user: build(:user), format: :json }
post api_users_path, params: params.to_json
end
it 'should create a new user' do
expect { create_user_request }.to change { User.count }.by(1)
end
But this fails with:
Failure/Error: params.require(:user).permit(:username, :name, :email, :password_digest)
ActionController::ParameterMissing:
param is missing or the value is empty: user
I think the issue is that params in the controller is a serialized JSON object as a string. If I replace params: params.to_json with params: params in my spec, then the user params becomes the string "#<User:0x.....>".
How do I make the spec and the controller play nice together?

Answer 1

I think the first issue is that you need to convert the model into a hash (not stringify it). The easiest way to do that is using .attributes i.e.
build(:user).attributes
I'm also not sure if you should be passing format: :json as part of the params, but I think it will depend on which version of rails, rspec etc you are using, but for rails 4 what works for me is
post api_users_path, user: build(:user).attributes, format: :json