Sometimes a small sample is really helpful in showing the differences between two approaches. Ruby on Rails is a slick web framework for building web applications the old way. When I say the old way, I mean building URLs manually and passing parameters through query strings manually, i.e. marshaling session data manually.
Rails automatically maps URLs to controllers and methods in those controllers to setup the appropriate models, and automatically binds the correct view for that method, based on naming conventions of the files. It's a great method and saves much of the hassle of writing a web app while enforcing a nice model view controller paradigm. Here's a sample any Rails programmer will probably recognize, first list.rhtml...
<% @recipes.each do |recipe| %> <tr> <td><%= link_to recipe.title, :action => "edit", :id => recipe.id %></td> <td><%= recipe.category.name %></td> <td><%= recipe.date %></td> </tr> <% end %> <p><%= link_to "Create new recipe", :action => "new" %></p>
and its controller...
class RecipieController < ApplicationController def list @recipies = Recipie.find(:all) end def edit @recipie = Recipie.find(@params[:id]) end end
Nice and clean, but the programmer is still working in a template language, requiring constant context switching between Ruby and HTML, and still manually building anchor tag URLs by calling a method and passing in the recipe's id. Passing around ids requires that the next view, bound to the edit method in the controller, needs to look up the object from the database with that id from reading the request parameters. You can see this in the edit method of the controller, it sets up data in an instance variable in the controller so the view will have access to it.
This is classic web development done very cleanly, and honestly very Smalltalk'ish, however, passing around an object id isn't very object oriented (it's rather relational actually), and context switching between two languages while working in the view isn't very fun. Instead of passing around an objects id why not pass around the object instead?
Enter Seaside, same code, different approach, more object oriented...
renderListOn: html self recipes do: [:recipe | self renderRecipe: recipe on: html ]. html paragraph: [html anchor callback:[self editRecipe: Recipe new]; with: 'Create new Recipe'] renderRecipe: aRecipe on: html html tableRow id: #recipie, aRecipe id; with: [html tableData: [html anchor callback:[self editRecipe: aRecipe]; with: aRecipe title]; tableData: aRecipe category name; tableData: aRecipe date ]
and the controller code...
recipies ^recipes ifNil:[recipes := Recipe findAll] editRecipe: aRecipe self call: (RecipeEditor for: aRecipe)
Seaside puts the view and controller together in one class, the component, and it can do so cleanly because there is no templating language, rendering views are simply method calls in pure Smalltalk. So instead of having a controller, with a bunch of RHTML files and partials, we have components (aka view/controllers), with rendering methods (aka partial views).
It's important to note however, that view code and controller code are still normally kept quite separate and organized using Smalltalk's method categories. View methods are normally categorized as "rendering", or something more specific like "rendering ajax", while controller code is categorized in categories like "actions", "queries", "accessing", or whatever categories you make up to keep your code organized. This is one of those Smalltalk things that no other language really has, and only exists in its environment so it doesn't translate to sample code.
Now, the main thing to note here, is that objects are passed between views as actual objects using a constructor on the view (RecipeEditor for: recipe). One component simply creates and calls another. The components are also rendered in pure Smalltalk, which means they can be factored into smaller more reusable methods (aka partials), using all of Smalltalk's existing tools, i.e. the refactoring browser. This is amazingly productive.
The anchor tag has a closure attached to it via its #callback: method, containing the actual code we want to execute when the user clicks the link. This closure, or block as Smalltalkers call them, gets turned into a URL automatically by Seaside and stored as a continuation on the current session. This means that RecipieEditor view doesn't need to go back to the database and look up the recipe by its id, because it was given the actual recipe object directly (less load on the database). In essence, instead of passing a bunch of state through a URL manually, you simply say when this link is pressed, execute this code. This is a technique discussed by Paul Graham in his essay Beating the Averages that he used in ViaWeb. This one change drastically changes the way one thinks about, and builds, web applications and makes programming much simpler.
Notice how I've factored out the rendering of a single row into its own method. This sets me up to do some nice simple Ajax updates of individual row by being able to pass an Ajax rendering canvas through that same #renderRecipeOn: method. For example, I could re-render just that row, via Ajax, when a hyper link is clicked with just this...
html anchor onClick: (html updater id: #recipe, self randomRecipe id; callback:[:ajax | self renderRecipe: self randomRecipe on: ajax]); with: 'Replace random recipe with another random recipe'
So when I write a page, I break it up into rendering methods based on which parts of the screen I want to update via Ajax. This is similar to what Rails does with partials, except Seaside does it with ordinary objects and methods. Top to bottom, objects and method calls in pure Smalltalk, no web stuff.
The price you pay... sessions and a little memory on the server. Yes it's harder to scale than a session-less approach like Rails, but it will scale, and memory is cheap these days, far cheaper than programmers. Seaside, like Rails, is a very opinionated framework. Seaside's opinion is that programming is the most expensive part of application development, so let's optimize development time instead of CPU memory and cycles and throw out the (stateless/templated html) model of web development in favor of simpler web development in one language, where you have all of your tools available and aren't constantly context switching between several languages.