#controller
class TopicsController < ApplicationController
  before_action :set_topic, only: [:show, :edit, :update, :destroy]

  # GET /topics
  # GET /topics.json
  def index
    @topics = Topic.all
  end

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

  # GET /topics/new
  def new
    @topic = Topic.new
  end

  # GET /topics/1/edit
  def edit
  end

  # POST /topics
  # POST /topics.json
  def create
    @topic = Topic.new(params[:topic])
    if @topic.save
      @topic = Topic.new(:name => params[:topic][:name], :last_poster_id => 1, :last_post_at => Time.now, :forum_id => params[:topic][:forum_id])

      if @topic.posts.first.save
        flash[:notice] = "Successfully created topic."
        redirect_to "/forums/#{@topic.forum_id}"
      else
        redirect :action => 'new'
      end
    else
      render :action => 'new'
    end
  end

  # PATCH/PUT /topics/1
  # PATCH/PUT /topics/1.json
  def update
    respond_to do |format|
      if @topic.update(topic_params)
        format.html { redirect_to @topic, notice: 'Topic was successfully updated.' }
        format.json { head :no_content }
      else
        format.html { render action: 'edit' }
        format.json { render json: @topic.errors, status: :unprocessable_entity }
      end
    end
  end

  # DELETE /topics/1
  # DELETE /topics/1.json
  def destroy
    @topic.destroy
    respond_to do |format|
      format.html { redirect_to topics_url }
      format.json { head :no_content }
    end
  end

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

    # Never trust parameters from the scary internet, only allow the white list through.
    def topic_params
      params.require(:topic).permit(:name, :last_poster_id, :last_post_at)
    end
end

#_form

<% form_for @topic do |f| %>

    <% @topic.errors.full_messages.each do |msg| %>
        <p><%= msg %></p>
    <% end %>

    <% if params[:forum] %><input type="hidden" id="topic_forum_id" name="topic[forum_id]" value="<%= params[:forum] %>" /><% end %>
    <p>
        <%= f.label :name %><br />
        <%= f.text_field :name %>
    </p>
    <p>
        <%= f.text_area(:post, :content, size: "20x30") %>
    </p>
    <p><%= f.submit "Create" %></p>
<% end %>

#error

Showing D:/Programacion/pfg/app/views/topics/_form.html.erb where line #13 raised:

wrong number of arguments (3 for 1..2)
Extracted source (around line #13):
10
11
12
13
14
15
16

           <%= f.text_field :name %>
       </p>
       <p>
           <%= f.text_area(:post, :content, size: "20x30") %>
       </p>
       <p><%= f.submit "Create" %></p>
   <% end %>