我的帖子模型：

before_create :owner
belongs_to :user
def owner
    self.user_id = current_user.id
end

但是这个dosent工作是因为我不能在model中使用current_user的方法.

这是我的控制器：

class PostsController < ApplicationController
before_filter :authenticate_user!

  # GET /posts
  # GET /posts.xml
  def index
    @posts = Post.all

    respond_to do |format|
      format.html # index.html.erb
      format.xml  { render :xml => @posts }
    end
  end

  # GET /posts/1
  # GET /posts/1.xml
  def show
    @post = Post.find(params[:id])

    respond_to do |format|
      format.html # show.html.erb
      format.xml  { render :xml => @post }
    end
  end

  # GET /posts/new
  # GET /posts/new.xml
  def new
    @post = Post.new

    respond_to do |format|
      format.html # new.html.erb
      format.xml  { render :xml => @post }
    end
  end

  # GET /posts/1/edit
  def edit
    @post = Post.find(params[:id])
  end

  # POST /posts
  # POST /posts.xml
  def create
    @post = Post.new(params[:post])

    respond_to do |format|
      if @post.save
        format.html { redirect_to(@post,:notice => 'Post was successfully created.') }
        format.xml  { render :xml => @post,:status => :created,:location => @post }
      else
        format.html { render :action => "new" }
        format.xml  { render :xml => @post.errors,:status => :unprocessable_entity }
      end
    end
  end

  # PUT /posts/1
  # PUT /posts/1.xml
  def update
    @post = Post.find(params[:id])

    respond_to do |format|
      if @post.update_attributes(params[:post])
        format.html { redirect_to(@post,:notice => 'Post was successfully updated.') }
        format.xml  { head :ok }
      else
        format.html { render :action => "edit" }
        format.xml  { render :xml => @post.errors,:status => :unprocessable_entity }
      end
    end
  end

  # DELETE /posts/1
  # DELETE /posts/1.xml
  def destroy
    @post = Post.find(params[:id])
    @post.destroy

    respond_to do |format|
      format.html { redirect_to(posts_url) }
      format.xml  { head :ok }
    end
  end
end

如何建立协会？所以,post user_id coloumn被分配了current_user.id