Design patterns

Rails
1

Hi everyone
I’m Maximiliano G. from Brazil and I am programing on ruby on
rails
only a couple of months.
I read a lot of books and articles about it but I could not clarify some
doubts about design patterns:

  1. Is it really good put some sql command on controller? because all
    articles that I see use sql into controllers, like:

    my controller

    @categories = Category.find :all, :conditions => ["date <= ? ",
    Date.today] :order => “name”

    Or Should I create methods on model?
    #my controller
    @categories = Category.find_all_before_date

    @#my model (date = Date.today)
    find :all, :conditions => ["date <= ? ", date] :order => “name”

  2. In my app I have some reports, like that:
    #report controller
    sql = <<EOF
    select categories.id, categories.name, sum(ledgers.value), sum(
    budgets.value)
    from categories, ledgers, budgets
    where categories.id = ledgers.category_id
    and categories.id = budgets.category_id
    group by categories.id, categories.name
    EOF

    So, Where should I put this sql? model or controller ?
    and How sould I execute it? using Category model?

    Category.find_by_sql(sql)

    or Is there way to use a generic model ?, some like that
    ActiveRecord::Base.find(sql)

cheers,

–
Atenciosamente,

Maximiliano Ferreira Guzenski
Sun Certified Java Programmer 1.4
Sun Certified Web Component Developer, Enterprise Edition 1.4

http://www.guzenski.com.br
[email protected]

2

  1. It’s all about agile development. If you find yourself using exactly
    that
    string, or very close to it, then look into moving it from the
    controller
    into the model. Make sure you have tests in place to verify that you
    didn’t
    break anything through this refactoring.

  2. For specific hard-coded SQL, probably best to put it in the model.
    Also,
    Model.find_by_sql is perfectly fine.

Hope that helps. Welcome to Rails!

Jason

3

Hi Maximiliano,

If you want to be strict about design patterns, then you want to keep
database queries and related find_by methods in the Model layer of
the MVC framework.

Also, that’s what the “Agile Development with Rails” book recommend.
Just a little extra point, you might want to use a more descriptive
name for the “sql” variable. It’s all about readability.

Cheers,
Mauricio

=== I’m brazilian, so here’s the same thing in Portuguese :wink: ====

Se você tá estudando design patterns e quer seguir os padrões, então
mantenha todos os métodos e buscas relacionados ao banco de dados na
camada de Modelo do padrão MVC.

O livro “Agile Development with Rails” também recomenda isso. Além
disso, eu recomendaria que você usasse um nome diferente pra sua
variável de busca, algo mais descritivo do que “sql”, pra facilitar a
releitura desse código.

Abração,
Mauricio

Mauricio L. Sadicoff
[email protected]

“Peace of mind isn’t at all superficial, really,” I expound. “It’s
the whole thing. That which produces it is good maintenance; that
which disturbs it is poor maintenance. What we call workability of
the machine is just an objectification of this peace of mind. The
ultimate test is always your own serenity.” - Zen and the Art of
Motorcycle Maintenance.

4

If your web application data is tied yo your web application, then you
could probably just have all your SQL in your model.

If you want to use the same data from outside of the web application,
then your model should be totally outside of Rails and just have a thin
model to your ‘real’ model.

The controller, in general, shouldn’t really know anything about the
underlying model. It just, in general, controls flow.

Also, MVC isn’t really a pattern, it;s a compound pattern. It’s made up
of other patterns. So, if you’re model is outside of Rails, you could
use an adapter from your thin model to your real model.

I hope this helps but as with everything, there’s more than one way to
do it, and everyone will have their angle on how MVC works. What’s good
for me, might not be good for you.

-Ants

Maximiliano G. [email protected] wrote: Hi everyone
I’m Maximiliano G. from Brazil and I am programing on ruby on
rails only a couple of months.
I read a lot of books and articles about it but I could not clarify some
doubts about design patterns:

  1. Is it really good put some sql command on controller? because all
    articles that I see use sql into controllers, like:

    my controller

    @categories = Category.find :all, :conditions => ["date <= ? ",
    Date.today] :order => “name”

    Or Should I create methods on model?
    #my controller
    @categories = Category.find_all_before_date

    @#my model (date = Date.today)
    find :all, :conditions => ["date <= ? ", date] :order => “name”

  2. In my app I have some reports, like that:
    #report controller
    sql = <<EOF
    select categories.id, categories.name , sum(ledgers.value),
    sum(budgets.value)
    from categories, ledgers, budgets
    where categories.id = ledgers.category_id
    and categories.id = budgets.category_id
    group by categories.id, categories.name
    EOF

    So, Where should I put this sql? model or controller ?
    and How sould I execute it? using Category model?

    Category.find_by_sql(sql)

    or Is there way to use a generic model ?, some like that
    ActiveRecord::Base.find(sql)

cheers,

–
Atenciosamente,

Maximiliano Ferreira Guzenski
Sun Certified Java Programmer 1.4
Sun Certified Web Component Developer, Enterprise Edition 1.4

http://www.guzenski.com.br
[email protected]

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5

just a comment on #1, +1 to everybody’s suggestion of keeping it in
the model. check out “Skinny Controller, Fat Model”:
http://weblog.jamisbuck.org/2006/10/18/skinny-controller-fat-model