Rails - Nov 2005 - HABTM loses 'additional fields' when using :include in find

Hi folks-

I''ve come across a snag that may be a bug, but I''m not sure...

When I do the following (example)--
   @members = @project.members.find(:all)

I get my @members array and it also has additional fields from the table 
"parts_members".  Great.

However, when I do:
   @members = @project.members.find(:all,
                                    :include => [ :state ])

where ''state'' is a field in the ''members''
table, for some reason those
additional fields get clobbered.  Am I doing something wrong?

   Jake

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

I don''t normally like to bump my own messages, but I''m still
having this
problem.  Has anyone else discovered it?

   Jake


Jake Janovetz wrote:
> Hi folks-
> 
> I''ve come across a snag that may be a bug, but I''m not
sure...
> 
> When I do the following (example)--
>    @members = @project.members.find(:all)
> 
> I get my @members array and it also has additional fields from the table 
> "parts_members".  Great.
> 
> However, when I do:
>    @members = @project.members.find(:all,
>                                     :include => [ :state ])
> 
> where ''state'' is a field in the
''members'' table, for some reason those
> additional fields get clobbered.  Am I doing something wrong?
> 
>    Jake

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

I think it''s a little unclear what you''re trying to do.
find(:include
=> ...) specifies table joins. For that to work, you would have to  
have an association already defined... example would be:

class Member < ActiveRecord::Base
   belongs_to :state
end

class State < ActiveRecord::Base
   has_many :members
end

If that is the case, by default you would have a `state_id'' field in  
Member (not a `state'' field) as a FK to the states table.  
Then, :include => [ :state ] should include that association.

If you''re doing what it looks like you''re trying to do (assign
an
enumerated value, State, to each member), you might want to look at  
the ActiveRecord Enumerations plugin (http://wiki.rubyonrails.com/ 
rails/pages/Plugins).
--
Brad Ediger
866-EDIGERS


On Nov 24, 2005, at 6:46 PM,
jakejanovetz-/E1597aS9LQAvxtiuMwx3w@public.gmane.org wrote:
> I don''t normally like to bump my own messages, but I''m
still having
> this
> problem.  Has anyone else discovered it?
>
>    Jake
>
>
> Jake Janovetz wrote:
>> Hi folks-
>>
>> I''ve come across a snag that may be a bug, but I''m
not sure...
>>
>> When I do the following (example)--
>>    @members = @project.members.find(:all)
>>
>> I get my @members array and it also has additional fields from the  
>> table
>> "parts_members".  Great.
>>
>> However, when I do:
>>    @members = @project.members.find(:all,
>>                                     :include => [ :state ])
>>
>> where ''state'' is a field in the
''members'' table, for some reason
>> those
>> additional fields get clobbered.  Am I doing something wrong?
>>
>>    Jake
>
>
> -- 
> Posted via http://www.ruby-forum.com/.
> _______________________________________________
> Rails mailing list
> Rails-1W37MKcQCpIf0INCOvqR/iCwEArCW2h5@public.gmane.org
> http://lists.rubyonrails.org/mailman/listinfo/rails

Hi Brad-

Sorry if this was confusing -- I''m still trying to figure out the best 
way to explain some of these database setups.

I have an association between tables ''projects'' and
''members''.  This
association is in a table called ''projects_members''.  The DB
would look
like:  (this is a simplified, made up database)

projects
--------
id
name

members
-------
id
name
state_id    --> Points to another table called ''states''

projects_members
----------------
project_id
member_id
some_other_column


According to the documentation, when the HABTM relationship is setup 
between ''projects'' and ''members'', the
''some_other_column'' is supposed to
magically appear as an attribute that I can read out.  The HABTM doc 
calls these "additional fields added to the join table".

This works just fine except when I use the '':include'' option
to
eager-load ''states''.  When I use :include, the
"additional fields" get
clobbered.

A workaround is to define a model for the join table, but this seems to 
be something that should work anyhow.  I''m also curious -- how often do
folks use HABTM rather than just define a model for the join table. 
Seems there''s always something in the join that makes it just a little 
outside the realm of HABTM.

   Jake


brad wrote:
> I think it''s a little unclear what you''re trying to do.
find(:include
> => ...) specifies table joins. For that to work, you would have to
> have an association already defined... example would be:
> 
> class Member < ActiveRecord::Base
>    belongs_to :state
> end
> 
> class State < ActiveRecord::Base
>    has_many :members
> end
> 
> If that is the case, by default you would have a `state_id'' field
in
> Member (not a `state'' field) as a FK to the states table.
> Then, :include => [ :state ] should include that association.
> 
> If you''re doing what it looks like you''re trying to do
(assign an
> enumerated value, State, to each member), you might want to look at
> the ActiveRecord Enumerations plugin (http://wiki.rubyonrails.com/
> rails/pages/Plugins).
> --
> Brad Ediger
> 866-EDIGERS

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

I haven''t really used HABTM much precisely for this reason...  
whenever the join-table information grows larger than just left_id  
and right_id, I''ve usually refactored it into a separate model. There  
is a sidebar from DHH in AWDWR about this, and it seems most people  
generally use separate models for this situation. (I actually can''t  
recall any situation in my Rails experience where a HABTM  
relationship has survived into production code without being replaced  
by a separate model.)

As to why the eager loading clobbers the additional fields, I''m not  
sure. I would suggest taking a look at the SQL queries being  
generated for the find()... maybe it''s joining the tables differently  
than you would expect.

Good luck--
be


On Nov 25, 2005, at 5:38 PM, Jake Janovetz
<jakejanovetz-/E1597aS9LQAvxtiuMwx3w@public.gmane.org>
wrote:
> Hi Brad-
>
> Sorry if this was confusing -- I''m still trying to figure out the
best
> way to explain some of these database setups.
>
> I have an association between tables ''projects'' and
''members''.  This
> association is in a table called ''projects_members''.  The
DB would
> look
> like:  (this is a simplified, made up database)
>
> projects
> --------
> id
> name
>
> members
> -------
> id
> name
> state_id    --> Points to another table called
''states''
>
> projects_members
> ----------------
> project_id
> member_id
> some_other_column
>
>
> According to the documentation, when the HABTM relationship is setup
> between ''projects'' and ''members'', the
''some_other_column'' is
> supposed to
> magically appear as an attribute that I can read out.  The HABTM doc
> calls these "additional fields added to the join table".
>
> This works just fine except when I use the '':include''
option to
> eager-load ''states''.  When I use :include, the
"additional fields" get
> clobbered.
>
> A workaround is to define a model for the join table, but this  
> seems to
> be something that should work anyhow.  I''m also curious -- how  
> often do
> folks use HABTM rather than just define a model for the join table.
> Seems there''s always something in the join that makes it just a
little
> outside the realm of HABTM.
>
>    Jake
>
>
> brad wrote:
>> I think it''s a little unclear what you''re trying to
do. find(:include
>> => ...) specifies table joins. For that to work, you would have to
>> have an association already defined... example would be:
>>
>> class Member < ActiveRecord::Base
>>    belongs_to :state
>> end
>>
>> class State < ActiveRecord::Base
>>    has_many :members
>> end
>>
>> If that is the case, by default you would have a `state_id''
field in
>> Member (not a `state'' field) as a FK to the states table.
>> Then, :include => [ :state ] should include that association.
>>
>> If you''re doing what it looks like you''re trying to
do (assign an
>> enumerated value, State, to each member), you might want to look at
>> the ActiveRecord Enumerations plugin (http://wiki.rubyonrails.com/
>> rails/pages/Plugins).
>> --
>> Brad Ediger
>> 866-EDIGERS
>
>