Rails - Sep 2009 - Strange behaviour with ActiveRecord and collection_ids

Hello, I don''t exactly know if this can be considered a bug, but before
posting it as a bug I''d like to see if there is a workaround

In my application, I have a couple of students and the subjects (matter
subjects) they choose. So far, I have 3 models:

class Student < ActiveRecord::Base
  has_many :options
  has_many :subjects, :through => :options
end

class Option < ActiveRecord::Base
  belongs_to :student
  belongs_to :subject
end

class Subject < ActiveRecord::Base
  has_many :options
  has_many :students, :through => :options
end


But, the problem is, not every student can choose any subject. So, I have a
couple of validations in the Student model (in my program, actually, things
are a bit more complicated), but there is a serious problem with this
approach: when I do, for example:

@student = Student.first
@student.subject_ids = [1, 2]

On the second line, ActiveRecord *saves* the associations on the database
(but doesn''t runs the Student validations), so I end with a invalid
student.
Is there a way to stop ActiveRecord from doing this?

Thanks in advance.

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Ok, I''ve seen on the rails documentation, it says clearly that what
I''m doing woudn''t work. But, in DataMapper, I can set the
value of,
say, @student.subjects and be sure it would just commit the changes to
the database when I save the model. Is this possible in ActiveRecord
too?


On Sep 30, 9:25 am, Maurício Szabo
<mauricio.sz...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:
> Hello, I don''t exactly know if this can be considered a bug, but
before
> posting it as a bug I''d like to see if there is a workaround
>
> In my application, I have a couple of students and the subjects (matter
> subjects) they choose. So far, I have 3 models:
>
> class Student < ActiveRecord::Base
>   has_many :options
>   has_many :subjects, :through => :options
> end
>
> class Option < ActiveRecord::Base
>   belongs_to :student
>   belongs_to :subject
> end
>
> class Subject < ActiveRecord::Base
>   has_many :options
>   has_many :students, :through => :options
> end
>
> But, the problem is, not every student can choose any subject. So, I have a
> couple of validations in the Student model (in my program, actually, things
> are a bit more complicated), but there is a serious problem with this
> approach: when I do, for example:
>
> @student = Student.first
> @student.subject_ids = [1, 2]
>
> On the second line, ActiveRecord *saves* the associations on the database
> (but doesn''t runs the Student validations), so I end with a
invalid student.
> Is there a way to stop ActiveRecord from doing this?
>
> Thanks in advance.