Rails 6.0.0 TypeError求助：POST API调用时nil转字符串失败

Let's break down what's causing this 500 error and the TypeError - no implicit conversion of nil into String, then fix it step by step:

Key Issues Identified #

• Mismatched Parameter Names: Your homework app sends data under the api_user key, but Devise (assuming you're using it for main app auth) expects parameters under your resource name (typically user for a User model). This confuses Warden's authentication logic.
• Incorrect Request Format: jQuery's $.post defaults to sending application/x-www-form-urlencoded data, not JSON. Even with the .json URL suffix, Rails might parse the data incorrectly, leading to silent authentication failures.
• Missing Devise Controller Setup: Your custom API Sessions controller doesn't define resource_name, so when you call sign_in(resource_name, resource), resource_name is nil—triggering the string conversion error.
• Uncaught Authentication Exceptions: Warden's authenticate! throws a Warden::NotAuthenticated exception on failure, which your code doesn't rescue. This leads to an unhandled server error instead of a proper 401 response.

Step-by-Step Fixes #

1. Update the Homework App's API Request #

Fix parameter naming, send proper JSON, and correct DOM selectors (your original code targeted parent classes instead of the input fields):

var login = document.querySelector(".login")
login.addEventListener("click", function(){
  // Use the correct input selectors from your form
  var email = document.querySelector(".mail-input")
  var password = document.querySelector(".pw-input")
  
  // Match the main app's expected parameter key (use `user` instead of `api_user`)
  let loginData = { user: { email: email.value.trim(), password: password.value.trim() } }
  
  $.ajax({
    url: "http://localhost:4000/api/login.json",
    method: "POST",
    contentType: "application/json", // Explicitly set JSON content type
    data: JSON.stringify(loginData), // Convert object to valid JSON string
    success: function(response){
      console.log("Login successful:", response)
      window.location.replace("http://localhost:3000/")
    },
    error: function(xhr){
      console.error("Login failed:", xhr.responseJSON)
    }
  })
})

2. Fix the Main App's Sessions Controller #

Update the controller to handle exceptions, define resource_name, and clean up control flow:

class Api::SessionsController < ApplicationController
  include Devise::Controllers::Helpers # Import Devise helper methods
  skip_before_action :verify_authenticity_token # Skip CSRF checks for API requests

  def create
    unless request.format == :json
      sign_out
      render status: 406, json: { message: "JSON requests only." }
      return
    end

    begin
      # Authenticate with Warden, catching failures to avoid 500 errors
      resource = warden.authenticate!(auth_options)
    rescue Warden::NotAuthenticated
      render status: 401, json: { response: "Access denied." }
      return
    end

    # Use explicitly defined resource_name to prevent nil errors
    sign_in(resource_name, resource)
    respond_with resource, location: after_sign_in_path_for(resource) do |format|
      format.json { render json: { success: true, jwt: current_token, response: "Authentication successful" } }
    end
  end

  private

  # Define your resource name (match your main app's user model, e.g., :user)
  def resource_name
    :user
  end

  # Configure Warden authentication scope
  def auth_options
    { scope: resource_name }
  end
end

3. Verify Routes & CORS Configuration #

• Routes: Ensure your main app's config/routes.rb has the correct API login route:

  namespace :api do
    post 'login', to: 'sessions#create'
  end
  

• CORS: Since your apps run on different ports, enable cross-origin requests in the main app:
  1. Add the rack-cors gem to your Gemfile and run bundle install.
  2. Create/update config/initializers/cors.rb:

     Rails.application.config.middleware.insert_before 0, Rack::Cors do
       allow do
         origins 'http://localhost:3000' # Your homework app's URL
         resource '*',
           headers: :any,
           methods: [:get, :post, :put, :patch, :delete, :options, :head]
       end
     end
     

After applying these changes, test the login flow again—you should no longer see the 500 error, and authentication should work as expected.

内容的提问来源于stack exchange，提问作者diego