What does self do in ruby on rails?

Question

I'm on railcasts just practicing some rails and have come across something I'm trying to understand.

I didn't get what the "self" on the authenticate method was doing. So I deleted it and tested the login of my app to see if it would show an error and it did:

error:

**NoMethodError in SessionsController#create
undefined method `authenticate' for #<Class:0x00000102cb9000**>

I would really appreciate if someone could explain exactly what that "Self" is doing. I was trying to figure out exactly what was going on but can't get my head around it.

Method is defined in model and called in sessions_controller.. I've been continuously deleting my app and starting from scratch to get the hang of it and many things make sense to me each time i start again but I'm stuck at "self".

I'm just the type of person who likes to understand why something works.

controller:

 def create
    user = User.authenticate(params[:email], params[:password])
    if user
      session[:user_id] = user.id
      redirect_to root_path, :notice => "Logged In"
    else
      flash.now.alert = "Invalid credentials"
      render "new"
    end
  end

model:

 def self.authenticate(email, password)
      user = find_by_email(email)
    if user && user.password_hash ==  BCrypt::Engine.hash_secret(password, user.password_salt)
      user
    else
      nil
    end
  end

Answer 1

This is a basic ruby question. In this case, self is used to define a class method.

    class MyClass
      def instance_method
        puts "instance method"
      end

      def self.class_method
        puts "class method"
      end
    end

Which are used like this:

    instance = MyClass.new
    instance.instance_method

Or:

    MyClass.class_method

Hope that clears things up a little bit. Also refer to: http://railstips.org/blog/archives/2009/05/11/class-and-instance-methods-in-ruby/