How to delete data in in project table and task table with just a relational id?

[Exequiel]

Hi I have 2 tables in database, and i want to know how i can delete the data in tasks table after i delete the data in projects table, the task table is connected by a project_id in projects table's id,

heres the tables. . .

[B] Table for projects"[/B]
   Column   |            Type             |                       Modifiers                       
------------+-----------------------------+-------------------------------------------------------
[B]id[/B]         | integer                     | not null default nextval('projects_id_seq'::regclass)
title      | character varying(255)      | 
description | character varying(255)      | 
user_id    | integer                     | 
created_at | timestamp without time zone | not null
updated_at | timestamp without time zone | not null
addbyemail | character varying(255)      |  

                                      [B] Table for tasks"[/B]
     Column      |            Type             |                     Modifiers                      
------------------+-----------------------------+----------------------------------------------------
id               | integer                     | not null default nextval('tasks_id_seq'::regclass)
todo             | character varying(255)      | 
[B]project_id[/B]       | integer                     | 
assigned_user_id | integer                     | 
created_at       | timestamp without time zone | not null
updated_at       | timestamp without time zone | not null

i want to delete the data using rails.

heres my code in db/migrate for projects table

class CreateProjects < ActiveRecord::Migration
  def change
    create_table :projects do |t|
      t.string :title
      t.string :decription
      t.integer :user_id

      t.timestamps
    end
  end
end

migration for tasks table

class CreateTasks < ActiveRecord::Migration
  def change
    create_table :tasks do |t|
      t.string :todo
      t.integer :project_id
      t.integer :assigned_user_id

      t.timestamps
    end
  end
end

heres my code in my app/controllers/projects_contro ller.erb

def destroy
    @project = Project.find(params[:id])
    @project.destroy

    respond_to do |format|
      format.html { render action: 'show' }
      format.json { render :json => { :status => 'Ok', :message => 'Project was successfully Deleted'} }
    end
  end

Please help me. any body please? tank you so much...