filter

define the actions to do before(after) some actions

two define syntaxes:

1. use method to define filter

2. use class to define filter

before_filter:

define the actions to do before some actions

ex:

before_filter :check

do check before any action. 

If check return false,  the action is not done

after_filter:

define the actions to do after some actions

filter & inheritance :

B extends A, then A's filter is done first, then B's filter is done

filter's scope:

only for some actions:

ex:

before_filter :check,  :only=>:index

before_filter :check,  :only=>[:index,  :new]

not for some actions:

before_filter :check,  :except=>:index

around_filter:

the combination of before_filter & after_filter

ex:

class TestFilter

    def  before(controller)

         @name="peter"

    end

    def  after(controller)

         @name ="andy"

    end

end

around filter  TestFilter.new