Rails - Nov 2010 - Rails 3 ActiveRecord queries - I'm missing something very BIG

Hi,

I know I am missing something very big regarding the changes with
respect to activerecord in Rails 3.

I can''t find the explanation. And I''m sure someone will kick
my ass for
not
finding the right piece of info in the docs and guides. Please do.

I have a working piece of code but I don''t like it.

So. Very basic association:

class Project < ActiveRecord::Base
  has_many :tasks
end

class Task < ActiveRecord::Base
  belongs_to :project
end


The task table has the foreign key:
t.integer  "project_id"


I can create a task this way, and the resulting task has the correct
project id stored

@project = Project.find(1)
@task = @project.tasks.build(params[:task])
@task.save


Now I get the project record using the Rails 2 way:

@project = Project.find(1) triggers:
Project Load (0.2ms)  SELECT `projects`.* FROM `projects` WHERE
(`projects`.`id` = 1) LIMIT 1

@project.inspect outputs:
#<Project id: 1, name: "test", created_at: "2010-11-18
15:15:23",
updated_at: "2010-11-18 15:15:23">

@project.tasks.inspect shows:
[#<Task id: 1, title: "test", project_id: 1, created_at:
"2010-11-18
15:20:06", updated_at: "2010-11-18 15:20:06">]

But now I want to use the Rails 3 way:

@proj = Project.where(:id => params[:id]) trigger:
Project Load (0.3ms)  SELECT `projects`.* FROM `projects` WHERE
(`projects`.`id` = 1)

@proj.inspect shows:
[#<Project id: 1, name: "test", created_at: "2010-11-18
15:15:23",
updated_at: "2010-11-18 15:15:23">]

And @proj.tasks.inspect gives:
NoMethodError (undefined method `tasks'' for
#<ActiveRecord::Relation:0x00000103922f30>):


Now, if I use:
@proj[0].tasks.inspect then I get the tasks for the project.

Is this the right way? I have the feeling it is not.

Cheers.

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On Nov 18, 2010, at 1:13 PM, comopasta Gr wrote:
> Hi,
> 
> I know I am missing something very big regarding the changes with
> respect to activerecord in Rails 3.
> 
> I can''t find the explanation. And I''m sure someone will
kick my ass for
> not
> finding the right piece of info in the docs and guides. Please do.
> 
> I have a working piece of code but I don''t like it.
> 
> So. Very basic association:
> 
> class Project < ActiveRecord::Base
>  has_many :tasks
> end
> 
> class Task < ActiveRecord::Base
>  belongs_to :project
> end
> 
> 
> The task table has the foreign key:
> t.integer  "project_id"
> 
> 
> I can create a task this way, and the resulting task has the correct
> project id stored
> 
> @project = Project.find(1)
> @task = @project.tasks.build(params[:task])
> @task.save
> 
> 
> Now I get the project record using the Rails 2 way:
> 
> @project = Project.find(1) triggers:
> Project Load (0.2ms)  SELECT `projects`.* FROM `projects` WHERE
> (`projects`.`id` = 1) LIMIT 1
> 
> @project.inspect outputs:
> #<Project id: 1, name: "test", created_at: "2010-11-18
15:15:23",
> updated_at: "2010-11-18 15:15:23">
> 
> @project.tasks.inspect shows:
> [#<Task id: 1, title: "test", project_id: 1, created_at:
"2010-11-18
> 15:20:06", updated_at: "2010-11-18 15:20:06">]
> 
> But now I want to use the Rails 3 way:
> 
> @proj = Project.where(:id => params[:id]) trigger:
> Project Load (0.3ms)  SELECT `projects`.* FROM `projects` WHERE
> (`projects`.`id` = 1)
> 
> @proj.inspect shows:
> [#<Project id: 1, name: "test", created_at: "2010-11-18
15:15:23",
> updated_at: "2010-11-18 15:15:23">]
where() is returning an array of objects.  That''s not technically
accurate, but once you ask for the result of where() using all or inspect or
anything else, it gets turned into an array.

There''s nothing wrong with writing Project.find(params[:id]) for
finding a specific instance...

> 
> And @proj.tasks.inspect gives:
> NoMethodError (undefined method `tasks'' for
> #<ActiveRecord::Relation:0x00000103922f30>):
> 
> 
> Now, if I use:
> @proj[0].tasks.inspect then I get the tasks for the project.
> 
> Is this the right way? I have the feeling it is not.
> 
> Cheers.
> 
> -- 
> Posted via http://www.ruby-forum.com/.
> 
> -- 
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Thanks Philip!

Yeah I wanted to include the tasks while getting the project.

I think this does it Rails 3 way:
@proj = Project.includes(:tasks).find_by_id(params[:id])

@proj.tasks returns the array of tasks and looks much better.

Cheers.

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On 18 November 2010 22:24, comopasta Gr
<lists-fsXkhYbjdPsEEoCn2XhGlw@public.gmane.org>
wrote:
> Thanks Philip!
>
> Yeah I wanted to include the tasks while getting the project.
>
> I think this does it Rails 3 way:
> @proj = Project.includes(:tasks).find_by_id(params[:id])
>
> @proj.tasks returns the array of tasks and looks much better.
Just a note to point out that the .includes(:tasks) is not required.
@proj.tasks will still work without it (unless this has changed in
rails 3).  Using includes will reduce the number of hits on the db
however.

Colin

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On Nov 19, 8:57 am, Colin Law
<clan...-gM/Ye1E23mwN+BqQ9rBEUg@public.gmane.org>
wrote:
> On 18 November 2010 22:24, comopasta Gr
<li...-fsXkhYbjdPsEEoCn2XhGlw@public.gmane.org> wrote:
>
> > Thanks Philip!
>
> > Yeah I wanted to include the tasks while getting the project.
>
> > I think this does it Rails 3 way:
> > @proj = Project.includes(:tasks).find_by_id(params[:id])
>
> > @proj.tasks returns the array of tasks and looks much better.
>
> Just a note to point out that the .includes(:tasks) is not required.
> @proj.tasks will still work without it (unless this has changed in
> rails 3).  Using includes will reduce the number of hits on the db
> however.
Except that when loading a single record it''s pretty pointless: a
second query is used to load the tasks, so there isn''t much point of
doing it ahead of time (of course if you were loading 20 projects it
would be a different matter)

Fred

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Frederick Cheung wrote in post #962548:
> On Nov 19, 8:57am, Colin Law
<clan...-gM/Ye1E23mwN+BqQ9rBEUg@public.gmane.org> wrote:
>>
>> Just a note to point out that the .includes(:tasks) is not required.
>> @proj.tasks will still work without it (unless this has changed in
>> rails 3). Using includes will reduce the number of hits on the db
>> however.
>
> Except that when loading a single record it''s pretty pointless: a
> second query is used to load the tasks, so there isn''t much point
of
> doing it ahead of time (of course if you were loading 20 projects it
> would be a different matter)
In other words, it sounds like (as in Rails 2) it''s generally better to
use joins than includes.

Not to hijack the thread, but: what''s the point of includes?  Why make
a
separate query when the DB could do it in one query with a join?  I''ve 
never understood this.  What, if anything, am I missing?
>
> Fred
Best,
-- 
Marnen Laibow-Koser
http://www.marnen.org
marnen-sbuyVjPbboAdnm+yROfE0A@public.gmane.org

Sent from my iPhone

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Hi,

Thanks for the comments. Yeah :include would make only when handling 
some amount of data to include. No much point if it is only a single 
task.

I checked with Mr. Bates and got a lesson about all this. For Rails 2 
but anyway the principle should be the same in Rails 3.

http://asciicasts.com/episodes/181-include-vs-joins

So as some of you pointed out joins is a better option in most of the 
cases, since you can pretty much achieve the same and gain more control.

Regards.

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On 19 November 2010 14:45, comopasta Gr
<lists-fsXkhYbjdPsEEoCn2XhGlw@public.gmane.org>
wrote:
> Hi,
>
> Thanks for the comments. Yeah :include would make only when handling
> some amount of data to include. No much point if it is only a single
> task.
>
> I checked with Mr. Bates and got a lesson about all this. For Rails 2
> but anyway the principle should be the same in Rails 3.
>
> http://asciicasts.com/episodes/181-include-vs-joins
>
> So as some of you pointed out joins is a better option in most of the
> cases, since you can pretty much achieve the same and gain more control.
However I think that in your example
@proj = Project.find_by_id(params[:id])
@tasks = @proj.tasks

neither is necessary.  Joins will do nothing for you, includes will
provide a small efficiency improvement over not including.

Colin

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