Associate user_id to the comment model?

问题

I use devise for authentication, I want to associate user_id to the comment model. It works when I send user_id as a parameter, But I want to set the current logined user's user_id automatically to the each comment. How can I do that?

#model/post.rb

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

#model/comment.rb

class Comment < ActiveRecord::Base

  belongs_to :post
end

#model/category.rb
   has_many :posts
#controllers/comments_controller

class CommentsController < ApplicationController
    before_action :set_comment, only: [:show, :edit, :update, :destroy]
    before_action :authenticate_user!


# GET /comments
# GET /comments.json
def index
  @comments = Comment.all
end

# GET /comments/1
# GET /comments/1.json
def show
end

# GET /comments/new
def new
  @comment = Comment.new
end

# GET /comments/1/edit
def edit
end

# POST /comments
# POST /comments.json
def create
  @comment = Comment.new(comment_params)

  respond_to do |format|
    if @comment.save
      format.html { redirect_to @comment, notice: 'comment was successfully created.' }
      format.json { render :show, status: :created, location: @comment }
    else
      format.html { render :new }
      format.json { render json: @comment.errors, status: :unprocessable_entity }
    end
  end
end

# PATCH/PUT /comments/1
# PATCH/PUT /comments/1.json
def update
  respond_to do |format|
    if @comment.update(comment_params)
      format.html { redirect_to @comment, notice: 'comment was successfully updated.' }
      format.json { render :show, status: :ok, location: @comment }
    else
      format.html { render :edit }
      format.json { render json: @comment.errors, status: :unprocessable_entity }
    end
  end
end

# DELETE /comments/1
# DELETE /comments/1.json
def destroy
  @comment.destroy
   respond_to do |format|
    format.html { redirect_to comments_url, notice: 'comment was successfully destroyed.' }
     format.json { head :no_content }
  end
end

private
  # Use callbacks to share common setup or constraints between actions.
  def set_comment
    @comment = Comment.find(params[:id])
  end

  # Never trust parameters from the scary internet, only allow the white list through.
  def comment_params
    params.require(:comment).permit(:rating, :comment, :post_id, :user_id)
  end
 end