Rails - Dec 2010 - Called id for nil, which would mistakenly be 4 -- if you really wanted the id of nil, use object_id

Hey all,

I know that this:

Called id for nil, which would mistakenly be 4 -- if you really wanted
the id of nil, use object_id

means that I have an instance variable that has not been initialized.
However, I''m a little confused as to what to do in a signup form for
form_for:

<% content_for :login do %>
   <% form_for @user, :url => { :action => "login" } do |f| 
%>
    <%= error_messages_for ''user'' %><br/>
    <%= f.label(:user_login, "Username")%>
     <%= f.text_field(:login) %><br/>
     <%= f.label(:user_password, "User Password")%>
    <%= f.password_field(:password) %><br/>
    <%= f.submit("Sign Up") %>

    <%= link_to ''Register'', :action =>
''signup'' %> |
      <%= link_to ''Forgot my password'', :action =>
''forgot_password'' %>
  <% end %>
 <% end %>

Because I didn''t declare @user in login method:

  def login
    if request.post?
      if session[:user] = User.authenticate(params[:user][:login],
params[:user][:password])
        flash[:message]  = "Login successful"
        redirect_to_root
      else
        flash[:warning] = "Login unsuccessful"
      end
    end

  end

There is no @user and so interpreter throws the exception. However, what
can I do in order to allow someone the opportunity to signin when using
a form? Do I create a temporary blank user: @user = User.new?

Thanks for response.

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You could do something like....

<%= form_for :user, :url=>{ blablabla } do |f| %>
  (...)
<% end %>

:-)

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John Merlino wrote in post #969678:
> Hey all,
>
> I know that this:
>
> Called id for nil, which would mistakenly be 4 -- if you really wanted
> the id of nil, use object_id
>
> means that I have an instance variable that has not been initialized.
Well, it means that something tried to call nil.id .
> However, I''m a little confused as to what to do in a signup form
for
> form_for:
>
[...]
> There is no @user and so interpreter throws the exception. However, what
> can I do in order to allow someone the opportunity to signin when using
> a form? Do I create a temporary blank user: @user = User.new?
That''s one common way of doing it.  Almost every Rails tutorial does 
that at some point.
>
> Thanks for response.
Best,
-- 
Marnen Laibow-Koser
http://www.marnen.org
marnen-sbuyVjPbboAdnm+yROfE0A@public.gmane.org

Sent from my iPhone

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AFAIK, form_for need the @user object to determine the url.
if its a new then it would generate /users and POST method
if its already exist it generate /users with PUT method

i think that you can specify the URL like daze said,
if you create new @user, it wil redirect to create method (if you have REST
route)
unless you specify the route otherwise


On Tue, Dec 21, 2010 at 7:41 AM, John Merlino
<lists-fsXkhYbjdPsEEoCn2XhGlw@public.gmane.org> wrote:
> Hey all,
>
> I know that this:
>
> Called id for nil, which would mistakenly be 4 -- if you really wanted
> the id of nil, use object_id
>
> means that I have an instance variable that has not been initialized.
> However, I''m a little confused as to what to do in a signup form
for
> form_for:
>
> <% content_for :login do %>
>   <% form_for @user, :url => { :action => "login" } do
|f|  %>
>    <%= error_messages_for ''user'' %><br/>
>    <%= f.label(:user_login, "Username")%>
>     <%= f.text_field(:login) %><br/>
>     <%= f.label(:user_password, "User Password")%>
>    <%= f.password_field(:password) %><br/>
>    <%= f.submit("Sign Up") %>
>
>    <%= link_to ''Register'', :action =>
''signup'' %> |
>      <%= link_to ''Forgot my password'', :action =>
''forgot_password'' %>
>  <% end %>
>  <% end %>
>
> Because I didn''t declare @user in login method:
>
>  def login
>    if request.post?
>      if session[:user] = User.authenticate(params[:user][:login],
> params[:user][:password])
>        flash[:message]  = "Login successful"
>        redirect_to_root
>      else
>        flash[:warning] = "Login unsuccessful"
>      end
>    end
>
>  end
>
> There is no @user and so interpreter throws the exception. However, what
> can I do in order to allow someone the opportunity to signin when using
> a form? Do I create a temporary blank user: @user = User.new?
>
> Thanks for response.
>
> --
> Posted via http://www.ruby-forum.com/.
>
> --
> You received this message because you are subscribed to the Google Groups
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>
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> That''s one common way of doing it.
Yet, it worked. Basically, visitor makes a request URL, which Rails 
translates into a controller/action sequence. In order to determine fate 
of URL request, we create a rule that matches the URL path of the 
request and determine where to direct that request. It maps requests to 
action methods inside the controllers. The mapper method parses the 
query string as a hash. So when login is part of query string action 
based on user clicking link, a URL request is made, the mapper method in 
turn is called, and points the request to the login method of the users 
class:

  map.login "login", :controller => "users", :action
=> "login"

Since we are using named routing, Rails builds a helper method:


  <%= link_to "login", login_path %>

login method is called of UsersController class:

def login
    @user = User.new
    if request.post?
      if session[:user] = User.authenticate(params[:user][:login], 
params[:user][:password])
        flash[:message]  = "Login successful"
        redirect_to :root
      else
        flash[:warning] = "Username or password does not exist"
      end
    end

  end

We instantiate User class and assign the new instance to  instance 
variable @user. Hence, we have a @user object and since during 
instantiation, our new instance inherits from ActiveRecord, the
"blank"
instance in reality inherits getter setter methods translated from users 
table in database. Hence, we accept parameters in the query string that 
will translate to the data we need (e.g. login and password). Since the 
instance variable inherits from ActiveRecord, it has access to some of 
the built in rails helper methods like label, text_field, 
password_field, submit:

<% content_for :login do %>
   <% form_for @user, :url => { :action => "login" } do |f| 
%>
    <%= error_messages_for ''user'' %><br/>
    <%= f.label(:user_login, "Username")%>
     <%= f.text_field(:login) %><br/>
     <%= f.label(:user_password, "User Password")%>
    <%= f.password_field(:password) %><br/>
    <%= f.submit("Login") %>

    <%= link_to ''Register'', :action =>
''signup'' %> |
      <%= link_to ''Forgot my password'', :action =>
''forgot_password'' %>
  <% end %>
 <% end %>

The helper methods render html output. User inserts value and gets 
converted to a hash with key/value pairs corresponding to field in table 
to its value. Hence, we do the following in controller:

    if request.post?
      if session[:user] = User.authenticate(params[:user][:login], 
params[:user][:password])

When the form is submitted a POST HTTP request is made, and we call the 
class method authenticate on the User class object. We pass in the 
relevant query string information using the params hash.

The authenticate method in turn is called:

  def self.authenticate(login, pass)
       u=find(:first, :conditions=>["login = ?", login])
       return nil if u.nil?
       return u if User.encrypt(pass, u.salt)==u.hashed_password
       nil
     end

We use special syntax self to indicate this is a class method and not an 
instance method and therefore can only be called on the class itself. We 
pass our query string arguments into the authenticate argument 
definition as parameters (local variables) login and pass. We perform a 
sql query to our mysql database, searching first record of login field 
that matches value passed. We assign result to local variabnle u. If u 
is nil, we return nil, and the if statement''s argument will be
converted
to BOOLEAN false (which I believe is object not a primitive in ruby?):

if session[:user] = User.authenticate(params[:user][:login], 
params[:user][:password])

Hence, else statement is invoked:

        flash[:warning] = "Username or password does not exist"

Otherwise, we return u (the data set of current user):

       return u if User.encrypt(pass, u.salt)==u.hashed_password

We do this if the encrupt method returns a value equal to what the 
hashed_password method''s value is.

So returning u will convert the if booleon to true and if statement 
returns immediate block:

        flash[:message]  = "Login successful"
        redirect_to :root

The user is logged in successful.

One thing I forgot to mention is we assign the local variable u to the 
session :user:

      if session[:user] = User.authenticate(params[:user][:login], 
params[:user][:password])

Hence, the session has this user stored.

THis is a little unclear to me though:
 session[:user]

We are storing a symbol called :user in sesion associative array. So 
:user is initiaized with vaue of u (whcih is dataset we returned). 
What''s the purpose of using symbol here? Why can''t we use
something else
like a variable?

THanks for response.

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On Dec 21, 7:16 pm, John Merlino
<li...-fsXkhYbjdPsEEoCn2XhGlw@public.gmane.org> wrote:
> One thing I forgot to mention is we assign the local variable u to the
> session :user:
>
>       if session[:user] = User.authenticate(params[:user][:login],
> params[:user][:password])
>
> Hence, the session has this user stored.
>
> THis is a little unclear to me though:
>  session[:user]
>
> We are storing a symbol called :user in sesion associative array. So
> :user is initiaized with vaue of u (whcih is dataset we returned).
> What''s the purpose of using symbol here? Why can''t we use
something else
> like a variable?
Why would you want to? If you''re going to store something in the
session you might as well use a constant as the key. You don''t have
to, but you''d just be making life more complicated

Fred
>
> THanks for response.
>
> --
> Posted viahttp://www.ruby-forum.com/.
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