Rails - Mar 2006 - Adding objects to a :through association

So I''m one of those nasty people building a self-referential
habtm-like Association using the funky new :through stuff. This is
about users having friends, so here''s my user.rb:

class User < ActiveRecord::Base
  has_many :friendships, :foreign_key => ''user_id''
  has_many :friends, :through => :friendships, :source => :friend
end

And here''s my friendship.rb:

class Friendship < ActiveRecord::Base
  belongs_to :user
  belongs_to :friend, :class_name => ''User'', :foreign_key
=> ''friend_id''
end

Now, everything is working great as long as I create instances of
Friendship "manually". Really no problems whatsoever, everything is
working just perfectly.

However, simply moving one user into another user''s list of friends
does *not* seem to work:

  someone.friends << someoneelse   # nothing happens

Considering I''m not seeing any notes about collection.<< not
working
with :through associations, I''m wondering if this is specific to crazy
self-referential stuff like what I''m doing.

Any hints?

Danke!

--
http://www.mans.de

Hendrik Mans wrote:
> So I''m one of those nasty people building a self-referential
> habtm-like Association using the funky new :through stuff. This is
> about users having friends, so here''s my user.rb:
> 
> class User < ActiveRecord::Base
>   has_many :friendships, :foreign_key => ''user_id''
>   has_many :friends, :through => :friendships, :source => :friend
> end
> 
> And here''s my friendship.rb:
> 
> class Friendship < ActiveRecord::Base
>   belongs_to :user
>   belongs_to :friend, :class_name => ''User'',
:foreign_key => ''friend_id''
> end
> 
> Now, everything is working great as long as I create instances of
> Friendship "manually". Really no problems whatsoever, everything
is
> working just perfectly.
> 
> However, simply moving one user into another user''s list of
friends
> does *not* seem to work:
> 
>   someone.friends << someoneelse   # nothing happens
> 
> Considering I''m not seeing any notes about collection.<< not
working
> with :through associations, I''m wondering if this is specific to
crazy
> self-referential stuff like what I''m doing.
> 
> Any hints?
I don''t think you can create a join model record automatically by
adding
to a :through association. You have to create the friendship manually. 
When you think about it, that makes sense, since the main point of using 
a join model is to put other attributes in it. There''s nowhere to 
specify those attributes the way you''re trying to do it.

Try doing someone.friendships.create(:friend => friend_user) and see if 
that works.

--
Josh Susser
http://blog.hasmanythrough.com

-- 
Posted via http://www.ruby-forum.com/.

On 3/31/06, Josh Susser <josh@hasmanythrough.com>
wrote:
> Try doing someone.friendships.create(:friend => friend_user) and see if
> that works.
Yes, that works. I was just confused by the fact that there was no
mention of << not working with :through associations.
> When you think about it, that makes sense, since the main point of using
> a join model is to put other attributes in it. There''s nowhere to
> specify those attributes the way you''re trying to do it.
Yes, I generally agree. However, using :through already has a bunch of
advantages over simple habtm even without "rich" attributes that I
would want to fill manually. In this scenario, the only extra
attribute that I want is created_at, which is set automatically. I was
assuming that AR would create the association model instance
automatically, considering it could easy infer the class name etc.
from the given parameters.

Anyway, user.friendships.create() will work, I was just wondering really.

Thanks,
Hendrik

--
http://www.mans.de

Hi Hendrik,

as far as I know, :through associations are read-only.

It makes sense because the model you are going :through is
completely standalone and as such, it may have more than
just the two belongs_to associations you specify.

I.e. the has_many :through directive doesn''t capture enough information
to reliably create the model you are going :through.

Makes sense?
--
Trevor Squires
http://somethinglearned.com



On 31-Mar-06, at 10:41 AM, Hendrik Mans wrote:
> So I''m one of those nasty people building a self-referential
> habtm-like Association using the funky new :through stuff. This is
> about users having friends, so here''s my user.rb:
>
> class User < ActiveRecord::Base
>   has_many :friendships, :foreign_key => ''user_id''
>   has_many :friends, :through => :friendships, :source => :friend
> end
>
> And here''s my friendship.rb:
>
> class Friendship < ActiveRecord::Base
>   belongs_to :user
>   belongs_to :friend, :class_name => ''User'',
:foreign_key =>
> ''friend_id''
> end
>
> Now, everything is working great as long as I create instances of
> Friendship "manually". Really no problems whatsoever, everything
is
> working just perfectly.
>
> However, simply moving one user into another user''s list of
friends
> does *not* seem to work:
>
>   someone.friends << someoneelse   # nothing happens
>
> Considering I''m not seeing any notes about collection.<< not
working
> with :through associations, I''m wondering if this is specific to
crazy
> self-referential stuff like what I''m doing.
>
> Any hints?
>
> Danke!
>
> --
> http://www.mans.de
> _______________________________________________
> Rails mailing list
> Rails@lists.rubyonrails.org
> http://lists.rubyonrails.org/mailman/listinfo/rails

Lets say your association table has a position field -- and you need  
to order by the position and you also need to be able to update the  
position hows that handled?

Chris


On Mar 31, 2006, at 12:38 PM, Trevor Squires wrote:
> Hi Hendrik,
>
> as far as I know, :through associations are read-only.
>
> It makes sense because the model you are going :through is
> completely standalone and as such, it may have more than
> just the two belongs_to associations you specify.
>
> I.e. the has_many :through directive doesn''t capture enough  
> information
> to reliably create the model you are going :through.
>
> Makes sense?
> --
> Trevor Squires
> http://somethinglearned.com
>
>
>
> On 31-Mar-06, at 10:41 AM, Hendrik Mans wrote:
>
>> So I''m one of those nasty people building a self-referential
>> habtm-like Association using the funky new :through stuff. This is
>> about users having friends, so here''s my user.rb:
>>
>> class User < ActiveRecord::Base
>>   has_many :friendships, :foreign_key => ''user_id''
>>   has_many :friends, :through => :friendships, :source => :friend
>> end
>>
>> And here''s my friendship.rb:
>>
>> class Friendship < ActiveRecord::Base
>>   belongs_to :user
>>   belongs_to :friend, :class_name => ''User'',
:foreign_key =>
>> ''friend_id''
>> end
>>
>> Now, everything is working great as long as I create instances of
>> Friendship "manually". Really no problems whatsoever,
everything is
>> working just perfectly.
>>
>> However, simply moving one user into another user''s list of
friends
>> does *not* seem to work:
>>
>>   someone.friends << someoneelse   # nothing happens
>>
>> Considering I''m not seeing any notes about collection.<<
not working
>> with :through associations, I''m wondering if this is specific
to
>> crazy
>> self-referential stuff like what I''m doing.
>>
>> Any hints?
>>
>> Danke!
>>
>> --
>> http://www.mans.de
>> _______________________________________________
>> Rails mailing list
>> Rails@lists.rubyonrails.org
>> http://lists.rubyonrails.org/mailman/listinfo/rails
>
> _______________________________________________
> Rails mailing list
> Rails@lists.rubyonrails.org
> http://lists.rubyonrails.org/mailman/listinfo/rails

Hendrik,
Out of curiosity, what does your schema look like for Friendships?

Hendrik Mans <hendrik@mans.de> wrote: So I''m one of those nasty
people building a self-referential
habtm-like Association using the funky new :through stuff. This is
about users having friends, so here''s my user.rb:

class User < ActiveRecord::Base
  has_many :friendships, :foreign_key => ''user_id''
  has_many :friends, :through => :friendships, :source => :friend
end

And here''s my friendship.rb:

class Friendship < ActiveRecord::Base
  belongs_to :user
  belongs_to :friend, :class_name => ''User'', :foreign_key
=> ''friend_id''
end

Now, everything is working great as long as I create instances of
Friendship "manually". Really no problems whatsoever, everything is
working just perfectly.

However, simply moving one user into another user''s list of friends
does *not* seem to work:

  someone.friends << someoneelse   # nothing happens

Considering I''m not seeing any notes about collection.<< not
working
with :through associations, I''m wondering if this is specific to crazy
self-referential stuff like what I''m doing.

Any hints?

Danke!

--
http://www.mans.de
_______________________________________________
Rails mailing list
Rails@lists.rubyonrails.org
http://lists.rubyonrails.org/mailman/listinfo/rails


		
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It''s not specific to what you''re doing... I had the same
problem. I
may have this wrong, but I think :through associations are strictly  
read-only. What I''d do:

   someone.friendships.create(:friend => someone_else)

This is a little more pedantic, but closer to what''s happening in the  
database and perhaps your Friendship model: when you add someone to  
your list of friends, you''re creating a field in the friendships  
table. HABTM associations might allow you to use the line I''ve quoted?


-- Michael Daines


On Apr 5, 2006, at 7:17 PM, Wolfgang Borgon wrote:
> However, simply moving one user into another user''s list of
friends
> does *not* seem to work:
>
>   someone.friends << someoneelse   # nothing happens
>
> Considering I''m not seeing any notes about collection.<< not
working
> with :through associations, I''m wondering if this is specific to
crazy
> self-referential stuff like what I''m doing.