#75 Complex Forms Part 3

In this third and final episode on complex forms I will show you how to edit a project and multiple tasks all in one form. This includes removing and adding tasks dynamically as well. See the show notes for updated code.

<!-- projects/edit.rhtml -->
<% form_for :project, :url => project_path(@project), :html => { :method => 'put' } do |f| %>
  <%= render :partial => 'fields', :locals => { :f => f } %>
  <p><%= submit_tag "Update Project" %></p>
<% end %>

<!-- projects/new.rhtml -->
<% form_for :project, :url => projects_path do |f| %>
  <%= render :partial => 'fields', :locals => { :f => f } %>
  <p><%= submit_tag "Create Project" %></p>
<% end %>

<!-- projects/_fields.rhtml -->
<p>
  Name: <%= f.text_field :name %>
</p>
<div id="tasks">
  <%= render :partial => 'task', :collection => @project.tasks %>
</div>
<p><%= add_task_link "Add a task" %></p>


<!-- projects/_task.rhtml -->
<div class="task">
  <% fields_for_task(task) do |task_form| %>
  <p>
    Task: <%= task_form.text_field :name %>
    <%= link_to_function "remove", "$(this).up('.task').remove()" %>
  </p>
  <% end %>
</div>

# models/project.rb
class Project < ActiveRecord::Base
  has_many :tasks, :dependent => :destroy

  validates_presence_of :name
  validates_associated :tasks

  after_update :save_tasks

  def new_task_attributes=(task_attributes)
    task_attributes.each do |attributes|
      tasks.build(attributes)
    end
  end

  def existing_task_attributes=(task_attributes)
    tasks.reject(&:new_record?).each do |task|
      attributes = task_attributes[task.id.to_s]
      if attributes
        task.attributes = attributes
      else
        tasks.delete(task)
      end
    end
  end

  def save_tasks
    tasks.each do |task|
      task.save(false)
    end
  end
end


# models/task.rb
class Task < ActiveRecord::Base
  belongs_to :project
  validates_presence_of :name
end


# projects_controller.rb
def new
  @project = Project.new
  @project.tasks.build
end

def create
  @project = Project.new(params[:project])
  if @project.save
    flash[:notice] = "Successfully created project and tasks."
    redirect_to projects_path
  else
    render :action => 'new'
  end
end

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

def update
  params[:project][:existing_task_attributes] ||= {}

  @project = Project.find(params[:id])
  if @project.update_attributes(params[:project])
    flash[:notice] = "Successfully updated project and tasks."
    redirect_to project_path(@project)
  else
    render :action => 'edit'
  end
end


# projects_helper.rb
def fields_for_task(task, &block)
  prefix = task.new_record? ? 'new' : 'existing'
  fields_for("project[#{prefix}_task_attributes][]", task, &block)
end

def add_task_link(name) 
  link_to_function name do |page| 
    page.insert_html :bottom, :tasks, :partial => 'task', :object => Task.new 
  end 
end 

Validation
Displaying the validation errors can be tricky depending on your needs. It may be as simple as displaying the project validations:

<!-- projects/_fields.rhtml -->
<%= error_messages_for :project %>

This will mention if there are task validation errors, however it will not state exactly what the errors are because these are stored in each task model.

If you need to display the task error messages. One way is to do this:

<!-- projects/_task.rhtml -->
<% @task = task %>
<%= error_messages_for :task %>

The error_messages_for method requires an instance variable with the same name, so that is why it needs to be set right there. This is an ugly work around.