使用Rails 4的简单学习应用-课程/注册/用户无法使用

Question

I am trying to build a simple learning app with rails 4.

here are my models:

class User < ActiveRecord::Base
  has_many :enrollments
  has_many :lectures, through: :enrollments
  accepts_nested_attributes_for :enrollments
end


class Enrollment < ActiveRecord::Base
    belongs_to :user 
    belongs_to :lecture
end

class Lecture < ActiveRecord::Base
    has_many :enrollments 
    has_many :users, through: :enrollments
end

And here are my controllers

class EnrollmentsController < ApplicationController
    before_action :authenticate_user!


    def create 
        @enrollments = current_user.enrollments.build(enrollment_params)
        if @enrollments.save 
            flash[:success] = "You have successfully enrolled."
            redirect_to profile_path(current_user)
        else 
            flash[:danger] = "Please try again."
            redirect_to root_path
        end
    end

    private

        def enrollment_params 
            params.require(:enrollment).permit(:user_id, :lecture_id)
        end


end

Here are my views:

lectures/index.html.erb

 <% @lectures.each do |lecture| %>
            <%= image_tag lecture.picture.url(:medium) %>
            <p><%= truncate(lecture.description, length: 80) %> </p>
            <%= link_to "Enroll Now", {:action=>"create", :controller=>"enrollments"},  :method => :post %>
      <% end %>

The problem is that when you click on Enroll Now I have the following error:

ActionController::ParameterMissing in EnrollmentsController#create param is missing or the value is empty: enrollment

def enrollment_params 
            params.require(:enrollment).permit(:user_id, :lecture_id)
        end

How can i make it work? Need help please

Answer 1

In your lectures/index.html.erb file, you are not passing any data to the controller's action method.

<%= link_to "Enroll Now", {:action=>"create", :controller=>"enrollments"},  :method => :post %>

Might be better served with something a la

<%= link_to "Enroll Now", {:action=>"create", :controller=>"enrollments", :user_id => current_user.id**, :lecture_id => lecture.id},  :method => :post %>
# ** not sure how you snag the current user's id in your app but you'd need it. 

Also, take a look at Routing in Rails . There are some super handy helper methods you can use that will allow you to do something like this (this was done quickly and may not be totally accurate but is offered to show you how you can use a route's path helper to clean up the code and make it even more readable):

<%= link_to 'Enroll Now', enrollments_path({enrollment: { user_id: current_user.id, lecture_id: lecture.id }}), :method => :post %>