Rails%203%20In%20Action

Tracking changes
Put this new callback on a line directly above the after_create because it makes
sense to have all your callbacks grouped together and in the order that they’re
called in:
before_create :set_previous_state
Call the set_previous_state method for this callback, which you define at the bottom
of the Comment model just before the set_ticket_state method, like this:
def set_previous_state
self.previous_state = ticket.state
end
The previous_state= method you call here isn’t yet defined. You can define this
method by declaring that your Comment objects belongs_to a previous_state, which
is a State object. Let’s put this line with the belongs_to in your Comment model:
belongs_to :previous_state, :class_name => "State"
Here you use a new option for belongs_to: class_name. The field in your comments
table is called previous_state_id and so you call your association previous_state.
To tell Rails what class this associated record is, you must use the class_name option,
otherwise Rails will go looking for the PreviousState class.
With this belongs_to defined, you get the previous_state= method for free and
so your callback should work alright. There’s one way to make sure of this, and that’s
to attempt to display these transitions between the states in your view so that your feature
will potentially pass. You’ll now work on displaying these transitions.
10.3.3 Displaying changes
When you display a comment that changes a ticket’s state, you want to display this
state transition along with the comment.
To get this text to show up, add the following lines to app/views/comments/
_comment.html.erb underneath the h4 tag:
→
This is almost correct, but there’s a slight problem. Your callback
will set the previous_state regardless of what the current state is,
and in this case you can end up with something like figure 10.12.
To stop this from happening, you can wrap this code in an if
statement, like this:
→
Now this text will only show up when the previous state isn’t the same as the current
state.
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Figure 10.12
State transition
from itself to itself