Question

When I click on sign in link it should check for valid username and password and display the message on sign in partial page, which I am calling in colorbox as a popup, but I am not able to display error messages.

This is my loginController:

def login
  if request.post?
    @user = User.new(params[:user])
    user=User.authenticate(params[:username], params[:password])
    if user.nil?
    flash[:error] = 'Login unsuccessful'
        redirect_to :back
    else
        flash[:notice] = 'Login successful'
        session[:user] = user.id
        redirect_to :controller=>'users', :action => 'show',:username=>user.username
    end
  end    
end

User.rb:

def self.authenticate(username, pass)
  user = find(:first, :conditions=>["username = ?", username])
  return nil if user.nil?
  return user if User.hash_password(pass) == user.password && username == user.username
  nil
end

In my view page_sign_in.html.erb page

<%= form_for @user, :url=>{:controller=>"logins",:action=>"login"},:remote=>true,:html=>{ :onSubmit => "return checkSignupValidation()",:id=>"signin_form", :multipart=>true}  do |f| %> 

@user is giving error: undefined methodmodel_name’ for Nilclass`

Answer 1

Your problem is that there is no model for the login – there is none needed. You do not want to use form_for, use instead form_tag:

<%= form_tag controller: "logins", action: "login", etc.. do %>
  <%= text_field_tag :username %>
  <%= password_field_tag :password %>
<% end %>

Then I would recommend some improvments to your controller:

def login
  if request.post?
    user = User.authenticate(params[:username], params[:password])
    if user.nil?
        flash[:error] = 'Login unsuccessful'
        redirect_to :back #I try to avoid :back, it feels better to use a fixed path
    else
        flash[:notice] = 'Login successful'
        session[:user] = user.id
        redirect_to :controller=>'users', :action => 'show', :username=>user.username
    end
  end    
end

You do not need the @user variable, so just avoid a unneccessary database query. I do not know if it is so good to use :back, I always try to use a fixed path.