Ruby on Rails-嵌套关联-创建新记录

Question

I'm learning Rails (4.2 installed) and working on a social network simulation application. I have setup an one to many relation between Users and Posts and now I'm trying to add also Comments to posts. After multiple tries and following the documentation on rubyonrails.org I ended up with the following setup:

User Model

  has_many :posts, dependent: :destroy
  has_many :comments, through: :posts

Post Model

  belongs_to :user
  has_many :comments

Comment Model

  belongs_to :user

The comment is initiated from the Post show page, so the Post Controller has:

def show
    @comment = Comment.new
  end

Now the question is: in Comments Controller , what is the correct way to create a new record. I tried the below and many others, but without success.

def create

    @comment = current_user.posts.comment.new(comment_params)
    @comment.save

    redirect_to users_path

  end

(current_user is from Devise)

Also, afterwards, how can I select the post corresponding to a comment?

Thank you

Answer 1

You'll want to create a relation on Post , letting each Comment know "which Post it relates to." In your case, you'll likely want to create a foreign key on Comment for post_id , then each Comment will belong_to a specific Post . So, you'd add belongs_to :post on your Comment model.

So, your models become:

class User < ActiveRecord::Base
  has_many :posts, dependent: :destroy
  has_many :comments, through: :posts
end

class Post < ActiveRecord::Base
  belongs_to :user
  has_many :comments
end

class Comments < ActiveRecord::Base
  belongs_to :user
  belongs_to :post
end

Then, to create a Comment , you would want to do one of two things in your controller:

1. Load the Post corresponding to the Comment you are creating via the URI as a parameter.

2. Pass the Post ID along in the form in which calls the create method on Comment .

I personally prefer loading the Post from a parameter in the URI, as you'll have less checking to do as far as authorization for can the Comment in question be added to the Post - eg think of someone hacking the form and changing the ID for the Post that the form originally sets.

Then, your create method in the CommentsController would look like this:

def create
  @post = Post.find(post_id_param)

  # You'll want authorization logic here for
  # "can the current_user create a Comment
  # for this Post", and perhaps "is there a current_user?"

  @comment = @post.comments.build(comment_params)

  if @comment.save
    redirect_to posts_path(@post)
  else
    # Display errors and return to the comment
    @errors = @comment.errors
    render :new
  end
end


private

def post_id_param
  params.require(:post_id)
end

def comment_params
  params.require(:comment).permit(...) # permit acceptable Comment params here
end

Answer 2

Change your Comment model into:

class Comment < ActiveRecord::Base
  belongs_to :post
  belongs_to :user, through: :post
end

Pass the post_id from view template:

<%= hidden_field_tag 'post_id', @post.id %>

Then change your create action:

def create
  @post = Post.find(params[:post_id])
  @comment = @post.comments.build(comment_params)
  @comment.user = current_user
  redirect_to post_path(@post)
end