Rails response_with在索引和创建方法上的行为不同

Question

I am building a simple json API in Rails 3.1. I created a controller that has two functions:

class Api::DogsController < ActionController::Base
  respond_to :json, :xml
  def index
    respond_with({:msg => "success"})
  end

  def create
    respond_with({:msg => "success"})
  end
end

In routes.rb I have

namespace :api do 
  resources :dogs
end

When I make a get request to http://localhost:3000/api/dogs I get the correct json from above. When I make a post to the same url, I get a rails exception:

ArgumentError in Api::DogsController#create
Nil location provided. Can't build URI.
actionpack (3.1.0) lib/action_dispatch/routing/polymorphic_routes.rb:183:in `build_named_route_call`
actionpack (3.1.0) lib/action_dispatch/routing/polymorphic_routes.rb:120:in `polymorphic_url'
actionpack (3.1.0) lib/action_dispatch/routing/url_for.rb:145:in `url_for'

But if I change the create code to

def create
  respond_with do |format|
    format.json { render :json => {:msg => "success"}}
  end
end

it returns the json just fine.

Can someone explain what is going on here?

Answer 1

After coming across this issue myself and overcoming it, I believe I can supply an answer.

When you simply say:

def create
  respond_with({:msg => "success"})
end

What rails tries to do is "guess" a url that the newly created resource is available at, and place it in the HTTP location header . That guess fails miserably for a hash object (the location it deduces is nil, which leads to the error message you are seeing).

To overcome this issue, then, you would need to do the following:

def create
  respond_with({:msg => "success"}, :location => SOME_LOCATION)
end

Assuming that you know where the new resource is located. You can even specify "nil" as "SOME_LOCATION" and that will work (somewhat absurdly).

Answer 2

I had the problem myself.

It is, like Aubergine says, something related with the http location header.

Actually, rails seems to build this location using by default the show route .

If you don't have a show action , -which is weird in an API, but can happen (i think)`, then you have to set a location by yourself. I have no idea what is the standard in this case.

If it happens that you need a show route, then code it, and everything should work fine.

Cheers.

Answer 3

I have found that errors = {:error => @device.errors.full_messages} respond_with( errors, :status => :bad_request, :location => nil) works. The :location is required and setting it to nil helps when using with spec: expect(last_response.status).not_to eql 201 expect(last_response.location).to be_nil

The problem I was having is that I was not returning the errors hash, just the status. Adding the errors hash and setting the location myself solved it.