Rails Public Activity Gem - after create action controller

I am trying to make an app with Rails 4.

I have installed the public_activity gem.

I followed the Ryan Bates Railscast and took the controller based approach, and also the lighter Common option (as opposed to tracking the Model).

In my activities_controller I have:

class ActivitiesController < ApplicationController
  def index
      @activities = PublicActivity::Activity.order("created_at desc")
  end
end

In my project.rb, I have:

include PublicActivity::Common

In my projects controller, create action, I have:

def create
    logger.debug "xxx create project"
    #authorise @project
    @project = Project.new(project_params)
    @project.creator_id = current_user.id
    @project.users << current_user
    @project.create_activity :create, owner: current_user

    respond_to do |format|
      if @project.save

        format.html { redirect_to @project }
        format.json { render action: 'show', status: :created, location: @project }
      else
        format.html { render action: 'new' }
        format.json { render json: @project.errors, status: :unprocessable_entity }
      end
    end
  end

In my activity view - index, I have:

<% @activities.each do |activity| %>
        <div class="col-md-4">
          <div class="indexdisplay">

            <span class="indexheading"> 
              <%= link_to activity.owner.name, activity.owner if activity.owner %>
            </span>
            <span class="indexsubtext">                 
              <%= render_activity activity %>
            </span>

In my public activity (view folder)/project/_create.html.erb, I have:

<% if activity.trackable %>
  <%= link_to activity.trackable.name, activity.trackable %>
<% else %>
  which has since been removed
<% end %>

When I try this, it gives me a blank page (no new activities have been created). When I try to create a new project, I get stuck on submitting the form because I get this error:

ActiveRecord::RecordNotSaved at /projects
You cannot call create unless the parent is saved

The problem is this line in the create action of my projects controller.

@project.create_activity :create, owner: current_user

Is there somewhere else I can put this in the controller to make it run after the project is saved? I have read about call backs but they need to be in the model and I'd like to keep this process running from the controller.

As the error state, you are trying to create an activity to an unsaved Project. Move the creation of the activity after saving the @project:

def create
    logger.debug "xxx create project"
    #authorise @project
    @project = Project.new(project_params)
    @project.creator_id = current_user.id

    respond_to do |format|
      if @project.save

        @project.users << current_user
        @project.create_activity :create, owner: current_user

        format.html { redirect_to @project }
        format.json { render action: 'show', status: :created, location: @project }
      else
        format.html { render action: 'new' }
        format.json { render json: @project.errors, status: :unprocessable_entity }
      end
    end
  end