Rails - Aug 2011 - Trivial SQL query - how to do it with ActiveRecord?

Hi,

I''ve been trying to read ActiveRecord tutorials etc. but
haven''t
figured out how to get the information I want. Let''s say I have a
users who own one to many bookshelves and some of these bookshelves
contain books. Now I would like to get a list of books that belong to
user named Timeon:

SELECT books.name FROM books, shelves, users WHERE
books.shelve_id=shelves.id AND shelves.owner_id=users.id AND
users.name=''Timeon'';

The models would be something like this (from the top of my head, may
not be correct):

Class User < ActiveRecord::Base
  has_many :book_shelves
end

Class BookShelve < ActiveRecord::Base
  belongs_to :user
  has_many :books
end

Class Book < ActiveRecord::Base
  belongs_to :book_shelves
end

So, how to get a list of Book objects that belong to user named Timeon
with a single line of code? Most examples I''ve seen first find the
user, then they list the shelves etc. but I would expect something
this trivial to be simple to achieve with a single call.

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A classic HABTM!

Class User < ActiveRecord::Base
 has_many :books, :through => :book_shelves
end

Class BookShelve < ActiveRecord::Base
 belongs_to :user
 has_many :books
end

Class Book < ActiveRecord::Base
 belongs_to :user, :through => :book_shelves
end


You can get the list of books like so:

Book.where( :user => { :name => ? }, params[:username] )

refer these for more:
http://edgeguides.rubyonrails.org/association_basics.html#the-has_many-through-association
http://edgeguides.rubyonrails.org/active_record_querying.html#specifying-conditions-on-the-joined-tables

On Thu, Aug 18, 2011 at 4:30 PM, timeon
<tarmountamo-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
> Hi,
>
> I''ve been trying to read ActiveRecord tutorials etc. but
haven''t
> figured out how to get the information I want. Let''s say I have a
> users who own one to many bookshelves and some of these bookshelves
> contain books. Now I would like to get a list of books that belong to
> user named Timeon:
>
> SELECT books.name FROM books, shelves, users WHERE
> books.shelve_id=shelves.id AND shelves.owner_id=users.id AND
> users.name=''Timeon'';
>
> The models would be something like this (from the top of my head, may
> not be correct):
>
> Class User < ActiveRecord::Base
>  has_many :book_shelves
> end
>
> Class BookShelve < ActiveRecord::Base
>  belongs_to :user
>  has_many :books
> end
>
> Class Book < ActiveRecord::Base
>  belongs_to :book_shelves
> end
>
> So, how to get a list of Book objects that belong to user named Timeon
> with a single line of code? Most examples I''ve seen first find the
> user, then they list the shelves etc. but I would expect something
> this trivial to be simple to achieve with a single call.
>
> --
> You received this message because you are subscribed to the Google Groups
> "Ruby on Rails: Talk" group.
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> To unsubscribe from this group, send email to
>
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>
>
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Hi,

On Aug 18, 7:08 pm, Dheeraj Kumar
<a.dheeraj.ku...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:
> A classic HABTM!
Yes indeed - and Thank You! Solved the problem. I got confused by the
picture on the association basics -section: I thought Appointment was
the high level item "owning" Patients and Physicians, like what one
would draw in an UML diagram.

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