Rails%203%20In%20Action

Developing your first application
should note here that this doesn’t call the new action/method again 14 but only renders
the template.
You can make the creation of the @purchase object fail by adding a validation.
Let’s do that now.
1.2.7 Validations
You can add validations to your model to ensure that the data conforms to certain
rules or that data for a certain field must be present or that a number you enter must
be above a certain other number. You’re going to write your first code for this application
and implement both of these things now.
Open up your Purchase model and change the whole file to what’s shown in the
following listing.
Listing 1.7 app/models/purchase.rb
class Purchase < ActiveRecord::Base
validates_presence_of :name
validates_numericality_of :cost, :greater_than => 0
end
You use the validates_presence_of method to define a validation that does what it
says on the box: validates that the field has a value. The other validation method,
validates_numericality_of, does more than what it initially claims: it validates that
the cost attribute is a number and that it is greater than 0.
Let’s test out these validations by going back to http://localhost:3000/purchases,
clicking New Purchase, and clicking Create Purchase. You should see the errors shown
in figure 1.5.
Figure 1.5
Errors on purchase
14 To do that, you call redirect_to new_purchase_path, but that wouldn’t persist the state of the
@purchase object to this new request without some seriously bad hackery. By rerendering the template, you
can display information about the object if the object is invalid.
13