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Listing 5-14. belongs_to Declarations in app/models/registration.rb
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class Registration < ActiveRecord::Base belongs_to :user belongs_to :event end
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Listing 5-15. belongs_to, has_many, and has_and_belongs_to_many Declarations in app/models/event.rb
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class Event < ActiveRecord::Base belongs_to :user
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CHAPTER 5 ADVANCED ACTIVE RECORD: ENHANCING YOUR MODELS
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has_many :registrations has_many :attendees, :through => :registrations, :source => :user has_and_belongs_to_many :categories end
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Listing 5-16. has_many Declarations in app/models/user.rb
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class User has_many has_many has_many end < ActiveRecord::Base :events :registrations :activities, :through => :registrations, :source => :event
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You ll notice that we reworked how we are naming associations. One aspect of the Rails philosophy is that we should always be questioning and refactoring our code to work with best practices. So, in this incarnation, events that we are attending as a user are called activities, and events are events that we are hosting. So, as an added benefit, has_many :through allows us to easily have nice names on our associations. The :source option lets us define the source name of the association. In this case, the activity in question is an event, so we set the :source option accordingly. The through associations let us pretend that the middle table (registrations) doesn t exist. Let s play with this on the console to see how it works. We ll start by finding any event and creating a brand-new user that can register for the event:
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>> => >> => => event = Event.find(:first) #<Event:0x3258d2c> user = User.create(:login => 'simon', :email => 'simon@example.com', :password 'secret') #<User:0x3251b1c>
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Because this user is brand new, it won t have any registrations or activities at this point, nor will the event have any attendees. We can confirm this fact by asking:
>> => >> => >> => user.registrations.any false user.activities.any false event.attendees.any false
To register this user for an event, we simply create a new registration object like we would any association, and pass in the event we want to register for. We do this using registrations.create.
CHAPTER 5 ADVANCED ACTIVE RECORD: ENHANCING YOUR MODELS
>> user.registrations.create(:event => event) => #<Registration:0x323ffe8>
Let s reload the user object and interrogate it again. This time around, you ll see that we have a registration.
>> => >> => user.reload #<User:0x3251b1c> user.registrations.any true
Activities are what we re calling events that a user has registered for. Again, if we ask whether the user object has any activities, it will respond with true.
>> user.activities.any => true
The activities method returns an array of events (remember that when we declared the activities association, we specified that the :source was :event):
>> user.activities => [#<Event:0x3231ee8]
The event will now have an attendee. Let s reload the event object and take a look:
>> => >> => >> => event.reload #<Event:0x3258d2c> event.attendees.any true event.attendees.include (user) true
Building Conditions for Advanced Finding
In 4, we covered using the find class method in Active Record, along with most of its options. Now we are going to expand on different ways to build conditions for your find operations. Building conditions is one of the most important things you do with your models.
Using a Conditions Hash
The most basic condition style is the hash syntax. Active Record takes the Hash passed into the conditions option, and turns the keys into column names and the values into
CHAPTER 5 ADVANCED ACTIVE RECORD: ENHANCING YOUR MODELS
parameters to match. The hash syntax is useful only if you are trying to find an exact match. Run the following commands to try out the hash syntax.
>> Event.find( :all, :conditions => {:location => '174 Spadina', :occurs_on => '2007-01-01'} ) => [] # no results
The hash syntax works well for straightforward find operations where you use only
ANDs to join together the conditions (that is, all conditions must match). However, some-
times you need more flexibility than exact matches.
Using a SQL Fragment
To specify conditions, you can pass in a SQL fragment as a string that is sent directly to the query. You need to have a pretty decent knowledge of SQL to use this kind of syntax, but it does provide a lot of flexibility, and you can create arbitrarily complex SQL fragments if you re a SQL-ninja. Let s try the same find operation as in the previous section, but using a pure SQL condition fragment.
>> Event.find(:all, :conditions => "occurs_on = '2007-09-02'") => [#<Event:0xb73f63b4 @attributes={..."occurs_on"=>"2007-09-02"...}>]
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