Hello !
I have bought book Agile web development with Ruby on Rails and i have
come to the section: sessions.

I am having some problems figuring out what does each line of code do.
So i would be gratefull if somoeone would explain it to me.

First I have this:

session[:cart] ||=

Ok i understand the second part which creates new if there isnt an
existing one. but the firt part is what i dont understand.


:cart is because of the name of the model cart.rb ?
Can i add more models ? Something like session[:cart, :person] ?

One more thing i dont understand is this line


in add_to_cart function.
I understand in general that it finds the id but where can i find more
documentation about params and how it is used ?

I have a link but it seems to me like it
isnt full ? I check for params cant find it, check for session
something small and unusuable…

Please help me ! I want to learn but im stuck :frowning:


Hi Eric,

Product.find(params[:id]) selects the record whose primary key value
matches the id passed in the parameters.

So, if your url looks like http://railsapp/product/show/1,
params[:id] would be 1, and the corresponding record gets selected.

The symbol, :cart isn’t used because it matches the name of the
model. You can use any name for the session variables and can also
save multiple values in a session.



Thank you very much fr your fast reply.
Could you tell me the correct syntax for saving multiple values to a
session ?


Do you know where can i check this ?
I havent find any good documentation on session :frowning:


Though, I’ve used sessions till now, I’m confident that you could do
something like this…

session[:user] = User.find(‘eric’)
session[:cart] = Cart.find_and_add(‘item1’)

  • Chaitanya


It is not a good practice to save objects into the session for several
reasons. One is that you are unnecessarily impacting the performance,
also will run into problems when you have changed your model but the
sessions consists of the older version models, which is very difficult

So instead of storing the object you can store the id of the object in

describes the available session methods.


Eric wrote:

Do you know where can i check this ?
I havent find any good documentation on session :frowning:

While some of the documentation says it is only similar, in general use
you can think of the session as a simple Hash object. With any hash
object, you can add stuff to it for a new key by simply doing something

my_hash = hash.New
my_hash[:foo] = “bar”
my_hash[:everything] = 42

same is true for the “session hash”
session = hash.New
session[:foo] = “bar”
session[:everything] = 42
session[:my_blog_entry] =

You can make these keys up at will and add them as above. The
usefulness of the session hash is that stuff you put in there is
“remembered” from one action to another and also from one controller to
another. Wherever your user goes in the app, his session data goes with
him. Because of the way http works, this is not true for a simple
global variable. So, whenever you need to “remember” something outside
the boundaries of a single action in a single controller, you need to
save it (or a reference to it, such as an “id” that can be found later)
in the session “hash” as shown above.



Jeff P. wrote:

same is true for the “session hash”
session = hash.New
session[:foo] = “bar”

oops, stupid mistake. You don’t create a new session hash with, you just use the session object created by rails. I copied
that and pasted it below and forgot to remove that line.