Rails%203%20In%20Action

548 APPENDIX B Tidbits
You should get back the number 1 from this. If you didn’t have the id prefix in your
routes and instead had something like make-it-shiny, you would need to save this
string to a field in the table called something obvious like permalink by using a
before_create method; then rather than using find in places where you are searching
for an object, you would instead use find_by_permalink.
B.2 Attribute change tracking
When working with Active Record, you have the ability to check if a field has changed
since the last time you made reference to this record. Let’s try this now with a Project
object in the ticketee project by first launching rails console.
Within this console, let’s create a new Project object:
>> project = Project.new
On any ActiveRecord::Base descendant, you can call the changed? method to determine
if it has changed since it was created or found. Let’s call it:
>> project.changed?
=> false
In this case, the project hasn’t changed from when it was created and so the changed?
method returns false. If you set any attribute on this object, the changed? method
will return true:
>> project.name = "Ticketee"
=> "Ticketee"
>> project.changed?
=> true
Now if you want to know what fields have caused this change, you can just drop off the
question mark at the end of changed?, like this:
>> project.changed
=> ["name"]
As you can see here, this method returns an array containing the attributes which
have changed on this object. If you changed another attribute on this project, such as
created_at, it would also appear in this list:
>> project.created_at = Time.now
=> [current time]
>> project.changed
=> ["name", "created_at"]
If you wanted to know only if a single attribute has changed, there’s the *_changed?
methods for all attributes on the model. For instance, if you wanted to know if the
name attribute has changed, then you would call name_changed?:
>> project.name_changed?
=> true