Question

I’m starting with ruby on rails. I have a simple scaffold.

Here is my model:

class Pet < ActiveRecord::Base
  belongs_to :user
  belongs_to :petRace
  attr_accessible :birth, :exactAge, :nick
  def initialize
    birth = DateTime.now.in_time_zone.midnight
  end
end

the html code

<%= form_for @pet, :html => { :class => 'form-horizontal' } do |f| %>
  <div class="control-group">
    <%= f.label :nick, :class => 'control-label' %>
    <div class="controls">
      <%= f.text_field :nick, :class => 'text_field' %>
    </div>
  </div>
  <div class="control-group">
    <%= f.label :birth, :class => 'control-label' %>
    <div class="controls">
    <div class="input-append date datepicker" data-date="<%=@pet.birth.strftime("%d/%m/%Y") %>" data-date-format="dd/mm/yyyy">
        <%= f.text_field :birth, :class => 'input-append', :value => @pet.birth.strftime("%d/%m/%Y") %>
    <span class="add-on"><i class="icon-th"></i></span>
    </div>
  </div>

  <div class="form-actions">
    <%= f.submit nil, :class => 'btn btn-primary' %>
    <%= link_to t('.cancel', :default => t("helpers.links.cancel")),
                pets_path, :class => 'btn' %>
  </div>
<% end %>

the controller:

 def new
    @pet = Pet.new   
    respond_to do |format|
      format.html # new.html.erb
      format.json { render json: @pet }
    end
  end

I just replace the original code for the :birth attribute, as you can see here:

<%= f.text_field :birth, :class => 'input-append', :value => @pet.birth.strftime("%d/%m/%Y") %>

when i select the option new the birth property seems to be no value and i get this execption

undefined method `[]' for nil:NilClass


Extracted source (around line #11):

8:      
9:  </script>
10: <%end%>
11: <%= form_for @pet, :html => { :class => 'form-horizontal' } do |f| %>
12:   <div class="control-group">
13:     <%= f.label :nick, :class => 'control-label' %>
14:     <div class="controls">

 app/views/pets/_form.html.erb:11:in `_app_views_pets__form_html_erb__3291519358612565784_70159905628180'
app/views/pets/new.html.erb:4:in `_app_views_pets_new_html_erb__1494749415896629355_70159907398120'
app/controllers/pets_controller.rb:28:in `new'

It’s my understanding that the birth value is set with the actual date and time(in the initialize method). Am i wrong or missing something? When i edit a record i have no problem.

Thanks in advance.

Answer 1

There are a variety of ways to set a default value as @Rob mentioned in his comment.

A callback as @Dave mentioned in his comment is an OK idea, too.

I suspect the main reason the after_initialize approach isn’t working for you is that you need to explicitly use self as in self.birth = rather than birth =. Ruby thinks you are defining a local variable named birth rather than assigning a value to ActiveRecord’s attribute birth that is implemented via method_missing internally. This is why @pet.birth is nil even though it might appear that you assigned a value to it.

Also note that the after_initialize callback will be called even for persisted objects when you instantiate them by loading them from the database. It is also called after the attributes are assigned via initialize for new records. Thus to prevent the user-specified value from being trampled on by your default (for both persisted and new records), be sure to do something like this:

self.birth = value if birth.nil?

Emphasis on the if birth.nil?