How can I update another Model using a Callback? - ruby-on-rails

Question

I'm working with a Model called Recover. Prior to creating the model I would like to save the boolean attribute, Combo.occupied = true using the Recover.combo_id attribute as a reference.
It appears my SQL is executing the query properly, but it is not saving this attribute. How can I save Combo.occupied = true?
recover.rb:
before_create :checkin
protected
def checkin
x = Combo.find_by_id(combo_id).occupied =
true
end
Rails Console:
Started POST "/recovers" for 127.0.0.1
at 2011-01-06 17:07:24 -0800
Processing by
RecoversController#create as HTML
Parameters: {"utf8"=>"✓",
"authenticity_token"=>"o1Iu3Y9/rVBOZPoDUgVP/tRfQ8GxbdWC40DbPq9YxUE=",
"recover"=>{"combo_id"=>"4",
"email"=>"jz#marin.edu"},
"commit"=>"Create Recover"} Recover
Load (0.2ms) SELECT "recovers"."id"
FROM "recovers" WHERE
("recovers"."email" =
'justin.zollars#marin.edu') LIMIT 1
Recover Load (0.1ms) SELECT
"recovers"."id" FROM "recovers" WHERE
("recovers"."combo_id" = 4) LIMIT 1
Combo Load (0.5ms) SELECT "combos".*
FROM "combos" WHERE ("combos"."id" =
4) LIMIT 1 AREL (0.5ms) INSERT INTO
"recovers" ("locker_number", "email",
"requests", "created_at",
"updated_at", "combo_id") VALUES
(NULL, 'justin.zollars#marin.edu',
NULL, '2011-01-07 01:07:24.287072',
'2011-01-07 01:07:24.287072', 4)
Redirected to
http://localhost:3000/recovers/14
Completed 302 Found in 119ms
RecoversController#create
def create
#recover = Recover.new(params[:recover])
respond_to do |format|
if #recover.save
format.html { redirect_to(#recover, :notice =>
'Recover was successfully created.') }
format.xml { render :xml => #recover, :status => :created,
:location => #recover }
else
format.html { render :action => "new" }
format.xml { render :xml => #recover.errors, :status =>
:unprocessable_entity }
end
end
end

Answer 1

You need to call save for the new value to be written to the database:
def checkin
combo = Combo.find_by_id(combo_id)
combo.occupied = true
combo.save!
end
This is easier if you use update_attribute. Also, if you have a belongs_to relationship, you can dispense with the find:
belongs_to :combo
def checkin
if combo # true unless combo_id is nil
combo.update_attribute(:occupied,true)
end
end
Note that update_attribute bypasses validation. If you need to validate, use update_attributes(:occupied=>true) instead.