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Handling Categories in the Events Controller
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We need to let our controller know how to deal with categories. This is relatively easy. That said, it will likely be one of the most complex things you need to do in a typical controller, and to make it happen, we ll need to use a little Ruby-fu. Listing 6-19 shows how it s done. The new code is listed in bold.
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Listing 6-19. Create Action Modified in app/controllers/events_controller.rb
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def create @event = Event.new(params[:event]) unless params[:categories].blank @event.categories << Category.find(params[:categories]) end
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CHAPTER 6 ACTION PACK: WORKING WITH THE VIEW AND THE CONTROLLER
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if @event.save flash[:notice] = 'Event was successfully created.' redirect_to :action => 'index' else render :action => 'new' end end
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First, we check whether a list of category id values was submitted in the params hash:
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unless params[:categories].blank
If there are categories in the params, we take advantage of the fact that ActiveRecord::Base.find accepts an array of primary keys for record to find and returns an array of the objects it finds. We further take advantage of the append operator, <<, and use it to append the categories collection to the existing (empty) collection contained in @event.categories. The result is that we tack any selected categories on to the @event.categories collection, and Active Record takes care of the rest. We can then save our @event object as usual.
APPENDING TO ARRAYS
The append operator, <<, works with Ruby arrays. Here s a quick demonstration from irb (introduced in 4):
> ary = [1,2,3] => [1, 2, 3] > ary << 4 => [1, 2, 3, 4] > ary << 5 => [1, 2, 3, 4, 5]
For more information about Ruby arrays, see Appendix A.
When we receive an update request, we need to handle things a little differently. We can t just append new categories onto the existing collection, because some categories may have been deleted. The easiest way to handle this is to reset all the @event s category id values at once. When you use the has_and_belongs_to_many association, Active Record automatically adds a method called #{collection}_ids to both sides of the relationship, where #{collection} is the singular name of the collection. In the case of an Event that has_and_belongs_to_many categories, the category_ids method is added to every Event
CHAPTER 6 ACTION PACK: WORKING WITH THE VIEW AND THE CONTROLLER
instance. When used, it replaces the existing collection with objects whose primary keys match those supplied. Listing 6-20 shows how this is handled, again with the modified code in bold.
Listing 6-20. Update Action Modified in app/controllers/events_controller.rb
def update @event = Event.find(params[:id]) @event.attributes = params[:event] unless params[:categories].blank @event.category_ids = params[:categories] end if @event.save flash[:notice] = 'Event was successfully updated.' redirect_to :action => 'show', :id => @event else render :action => 'edit' end end
Instead of using the update_attributes method to update the Event object and save it in one fell swoop, we use attributes. The only difference between the two is that attributes doesn t automatically save the record. Since we want to avoid having to save twice (once to update the attributes via params and another time to update the categories), this makes sense. After the attributes have been set and the category_id values have been updated, we can save the record and respond accordingly to either success or failure.
Using Controller Filters
Filters provide a way for you to perform operations either before or after an action is invoked. There s even an around filter that can wrap the executing of an action. Of the three, the before filter is the most commonly used, so that s what we ll focus on here. Here s how it works: all the code you place in a before_filter will be run before the action in question is called. Pretty simple, really. But there s a catch: if the before_ filter returns false, the action will not be executed. We often use this to protect certain actions that require a login. In our users controller, we want the new, create, login, and logout actions to remain open (anyone can access them), but we want to restrict all other actions to logged-in users. Here s how we can do that using filters:
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