Rails - Apr 2008 - Help: odd results from many-to-many self-referential relationship with attribute in join table

I''m having an issue with the data returning from a self-referential
many-to-many relationship with an attribute in the join table that''s
being used to limit the query. I''ll explain what I''m doing
below which
will then bring you to the problem concerning the records I''m getting
back from the relationship.

MIGRATIONS (the two tables involved in the problem)

Note that in contained_gear_items there are three items related to
gic[1] and list_id 1 and two other items related to gic[1] but belong
to list_id 2 so I would think I wouldn''t see them (considering I have
''contained_gear_items.list_id" => 1'' in the conditions
- see below).
When looking at .contained_items the list_id = 1 constraint seems to
have been missed. But if I go directly into the contained_gear_items
join model I see only the three items, as I should. Any help would be
much appreciated.

so, data wise, contained_gear_item goes like this:

id	gear_item_id	contained_gear_item_id	list_id
1	4			9					2
2	4			10					2
5	4			5					1
6	4			6					1
7	4			7					1



#011_create_contained_gear_items.rb (migration)
class CreateContainedGearItems < ActiveRecord::Migration
  def self.up
    create_table :contained_gear_items do |t|
      t.integer "gear_item_id",           :null => false
      t.integer "contained_gear_item_id", :null => false
      t.integer "list_id",                :null => false
      t.integer "position"
      t.timestamps
    end
  end

## 001_create_gear_items.rb (migration)
class CreateGearItems < ActiveRecord::Migration
  def self.up
    create_table :gear_items do |t|
      t.string  "title",              :limit => 100,    :null =>
false
      t.boolean "is_container",       :default => false
      t.timestamps
    end
  end


MODELS

## gear_item.rb (model)
class GearItem < ActiveRecord::Base
  has_many :contained_gear_items
  has_many :contained_items, :through => :contained_gear_items


## contained_gear_item.rb (model)
class ContainedGearItem < ActiveRecord::Base
  belongs_to :gear_item
  belongs_to :contained_item, :class_name => ''GearItem'',
    :foreign_key => ''contained_gear_item_id''


IN THE SCRIPT/CONSOLE
>> gic = GearItem.find(
  :all,
  :include => "contained_gear_items",
  :conditions => {"contained_gear_items.list_id" => 1,
:is_container
=> true},
  :order => "contained_gear_items.position")
>> puts gic[1].contained_items
#<GearItem:0x3efeb80>
#<GearItem:0x3efeb30>
#<GearItem:0x3efeae0>
#<GearItem:0x3efea90>
#<GearItem:0x3efea40>
>> puts gic[1].contained_gear_items
#<ContainedGearItem:0x3f2c56c>
#<ContainedGearItem:0x3f29a4c>
#<ContainedGearItem:0x3f27328>

Thanks for any help you can provide...

Cheers







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On 7 Apr 2008, at 05:35, MaddyTheGoose wrote:
>
> I''m having an issue with the data returning from a
self-referential
> many-to-many relationship with an attribute in the join table
that''s
> being used to limit the query. I''ll explain what I''m
doing below which
> will then bring you to the problem concerning the records I''m
getting
> back from the relationship.
>
Your problem is only with the eager loading: when you load the has  
many through it does not use the already loaded contained_items to get  
the association, and so the conditions you specified at that point do  
not apply. You probably want to specify the conditions on the  
association itself, although I''m not entirely sure what you''re
trying
to do.

Fred
> MIGRATIONS (the two tables involved in the problem)
>
> Note that in contained_gear_items there are three items related to
> gic[1] and list_id 1 and two other items related to gic[1] but belong
> to list_id 2 so I would think I wouldn''t see them (considering I
have
> ''contained_gear_items.list_id" => 1'' in the
conditions - see below).
> When looking at .contained_items the list_id = 1 constraint seems to
> have been missed. But if I go directly into the contained_gear_items
> join model I see only the three items, as I should. Any help would be
> much appreciated.
>
> MODELS
>
> ## gear_item.rb (model)
> class GearItem < ActiveRecord::Base
>  has_many :contained_gear_items
>  has_many :contained_items, :through => :contained_gear_items
>
>
> ## contained_gear_item.rb (model)
> class ContainedGearItem < ActiveRecord::Base
>  belongs_to :gear_item
>  belongs_to :contained_item, :class_name =>
''GearItem'',
>    :foreign_key => ''contained_gear_item_id''
>
>
> IN THE SCRIPT/CONSOLE
>
>>> gic = GearItem.find(
>  :all,
>  :include => "contained_gear_items",
>  :conditions => {"contained_gear_items.list_id" => 1,
:is_container
> => true},
>  :order => "contained_gear_items.position")
>
>>> puts gic[1].contained_items
> #<GearItem:0x3efeb80>
> #<GearItem:0x3efeb30>
> #<GearItem:0x3efeae0>
> #<GearItem:0x3efea90>
> #<GearItem:0x3efea40>
>
>>> puts gic[1].contained_gear_items
> #<ContainedGearItem:0x3f2c56c>
> #<ContainedGearItem:0x3f29a4c>
> #<ContainedGearItem:0x3f27328>
>
> Thanks for any help you can provide...
>
> Cheers
>
>
>
>
>
>
>
> >

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First off, thanks for the help.

I did try adding the condition to the association itself but it didn''t
seem like the right place for it although I could be wrong (I am
pretty new to rails). I had it like this:

class GearItem < ActiveRecord::Base
  has_many :contained_gear_items
  has_many :contained_items, :through
=> :contained_gear_items, :conditions =>
"contained_gear_items.list_id
= 1"

which works as I wanted but shouldn''t the associations only deal with
the relationship but not so much with conditions (leaving the
conditions to the find)? I guess I''m looking for some best-practices
here. I want to be able to dynamically change the list_id. I may be
looking at this wrong and perhaps have to change the way I think if
the above is the right way to do it.

Is there a way to move the condition above into the find?

Essentially what I''m trying to achieve is:
A GearItem can contained 0..n GearItems and the GearItem->GearItem
relationship belongs to a list. So list 1 can have GearItem 1
containing GearItem 2 & 3 but list 2 can have GearItem 2 containing
GearItem 1 & 4, etc...



On Apr 7, 9:02 am, Frederick Cheung
<frederick.che...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:
> On 7 Apr 2008, at 05:35, MaddyTheGoose wrote:
>
>
>
> > I''m having an issue with the data returning from a
self-referential
> > many-to-many relationship with an attribute in the join table
that''s
> > being used to limit the query. I''ll explain what I''m
doing below which
> > will then bring you to the problem concerning the records I''m
getting
> > back from the relationship.
>
> Your problem is only with the eager loading: when you load the has
> many through it does not use the already loaded contained_items to get
> the association, and so the conditions you specified at that point do
> not apply. You probably want to specify the conditions on the
> association itself, although I''m not entirely sure what
you''re trying
> to do.
>
> Fred
>
> > MIGRATIONS (the two tables involved in the problem)
>
> > Note that in contained_gear_items there are three items related to
> > gic[1] and list_id 1 and two other items related to gic[1] but belong
> > to list_id 2 so I would think I wouldn''t see them
(considering I have
> > ''contained_gear_items.list_id" => 1'' in the
conditions - see below).
> > When looking at .contained_items the list_id = 1 constraint seems to
> > have been missed. But if I go directly into the contained_gear_items
> > join model I see only the three items, as I should. Any help would be
> > much appreciated.
>
> > MODELS
>
> > ## gear_item.rb (model)
> > class GearItem < ActiveRecord::Base
> >  has_many :contained_gear_items
> >  has_many :contained_items, :through => :contained_gear_items
>
> > ## contained_gear_item.rb (model)
> > class ContainedGearItem < ActiveRecord::Base
> >  belongs_to :gear_item
> >  belongs_to :contained_item, :class_name =>
''GearItem'',
> >    :foreign_key => ''contained_gear_item_id''
>
> > IN THE SCRIPT/CONSOLE
>
> >>> gic = GearItem.find(
> >  :all,
> >  :include => "contained_gear_items",
> >  :conditions => {"contained_gear_items.list_id" => 1,
:is_container
> > => true},
> >  :order => "contained_gear_items.position")
>
> >>> puts gic[1].contained_items
> > #<GearItem:0x3efeb80>
> > #<GearItem:0x3efeb30>
> > #<GearItem:0x3efeae0>
> > #<GearItem:0x3efea90>
> > #<GearItem:0x3efea40>
>
> >>> puts gic[1].contained_gear_items
> > #<ContainedGearItem:0x3f2c56c>
> > #<ContainedGearItem:0x3f29a4c>
> > #<ContainedGearItem:0x3f27328>
>
> > Thanks for any help you can provide...
>
> > Cheers
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On 7 Apr 2008, at 16:46, MaddyTheGoose wrote:
>
> First off, thanks for the help.
>
> I did try adding the condition to the association itself but it
didn''t
> seem like the right place for it although I could be wrong (I am
> pretty new to rails). I had it like this:
>
> class GearItem < ActiveRecord::Base
>  has_many :contained_gear_items
>  has_many :contained_items, :through
> => :contained_gear_items, :conditions =>
"contained_gear_items.list_id
> = 1"
>
> which works as I wanted but shouldn''t the associations only deal
with
> the relationship but not so much with conditions (leaving the
> conditions to the find)?
Not necessarily, it can definitely be used to good effect (eg customer  
has_many :orders and customer  
has_many :outstanding_orders, :conditions => ''...'')
> I guess I''m looking for some best-practices
> here. I want to be able to dynamically change the list_id. I may be
> looking at this wrong and perhaps have to change the way I think if
> the above is the right way to do it.
>
> Is there a way to move the condition above into the find?
> Essentially what I''m trying to achieve is:
> A GearItem can contained 0..n GearItems and the GearItem->GearItem
> relationship belongs to a list. So list 1 can have GearItem 1
> containing GearItem 2 & 3 but list 2 can have GearItem 2 containing
> GearItem 1 & 4, etc...
>
In this case having all the conditions in the association probably  
isn''t the right thing to do since you''d have to have one
association
per list and you''d have to figure out what to call them

You could do this via an association proxy, eg

has_many :contained_items, :through => :contained_gear_items do
   def from_list(n)
     find :all, :conditions => ["contained_gear_items.list_id = ?",
n]
   end
end

Then you can do stuff like foo.contained_items.from_list(23)

Fred
>
>
> On Apr 7, 9:02 am, Frederick Cheung
<frederick.che...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
> wrote:
>> On 7 Apr 2008, at 05:35, MaddyTheGoose wrote:
>>
>>
>>
>>> I''m having an issue with the data returning from a
self-referential
>>> many-to-many relationship with an attribute in the join table
that''s
>>> being used to limit the query. I''ll explain what
I''m doing below
>>> which
>>> will then bring you to the problem concerning the records
I''m
>>> getting
>>> back from the relationship.
>>
>> Your problem is only with the eager loading: when you load the has
>> many through it does not use the already loaded contained_items to  
>> get
>> the association, and so the conditions you specified at that point do
>> not apply. You probably want to specify the conditions on the
>> association itself, although I''m not entirely sure what
you''re trying
>> to do.
>>
>> Fred
>>
>>> MIGRATIONS (the two tables involved in the problem)
>>
>>> Note that in contained_gear_items there are three items related to
>>> gic[1] and list_id 1 and two other items related to gic[1] but  
>>> belong
>>> to list_id 2 so I would think I wouldn''t see them
(considering I
>>> have
>>> ''contained_gear_items.list_id" => 1'' in
the conditions - see below).
>>> When looking at .contained_items the list_id = 1 constraint seems
to
>>> have been missed. But if I go directly into the
contained_gear_items
>>> join model I see only the three items, as I should. Any help would
>>> be
>>> much appreciated.
>>
>>> MODELS
>>
>>> ## gear_item.rb (model)
>>> class GearItem < ActiveRecord::Base
>>> has_many :contained_gear_items
>>> has_many :contained_items, :through => :contained_gear_items
>>
>>> ## contained_gear_item.rb (model)
>>> class ContainedGearItem < ActiveRecord::Base
>>> belongs_to :gear_item
>>> belongs_to :contained_item, :class_name =>
''GearItem'',
>>>   :foreign_key => ''contained_gear_item_id''
>>
>>> IN THE SCRIPT/CONSOLE
>>
>>>>> gic = GearItem.find(
>>> :all,
>>> :include => "contained_gear_items",
>>> :conditions => {"contained_gear_items.list_id" =>
1, :is_container
>>> => true},
>>> :order => "contained_gear_items.position")
>>
>>>>> puts gic[1].contained_items
>>> #<GearItem:0x3efeb80>
>>> #<GearItem:0x3efeb30>
>>> #<GearItem:0x3efeae0>
>>> #<GearItem:0x3efea90>
>>> #<GearItem:0x3efea40>
>>
>>>>> puts gic[1].contained_gear_items
>>> #<ContainedGearItem:0x3f2c56c>
>>> #<ContainedGearItem:0x3f29a4c>
>>> #<ContainedGearItem:0x3f27328>
>>
>>> Thanks for any help you can provide...
>>
>>> Cheers
> >

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Love it. Just implemented it and it looks good so far...

Thanks again for the help, much appreciated.

On Apr 7, 11:59 am, Frederick Cheung
<frederick.che...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:
> On 7 Apr 2008, at 16:46, MaddyTheGoose wrote:
>
>
>
>
>
> > First off, thanks for the help.
>
> > I did try adding the condition to the association itself but it
didn''t
> > seem like the right place for it although I could be wrong (I am
> > pretty new to rails). I had it like this:
>
> > class GearItem < ActiveRecord::Base
> >  has_many :contained_gear_items
> >  has_many :contained_items, :through
> > => :contained_gear_items, :conditions =>
"contained_gear_items.list_id
> > = 1"
>
> > which works as I wanted but shouldn''t the associations only
deal with
> > the relationship but not so much with conditions (leaving the
> > conditions to the find)?
>
> Not necessarily, it can definitely be used to good effect (eg customer
> has_many :orders and customer
> has_many :outstanding_orders, :conditions => ''...'')
>
> > I guess I''m looking for some best-practices
> > here. I want to be able to dynamically change the list_id. I may be
> > looking at this wrong and perhaps have to change the way I think if
> > the above is the right way to do it.
>
> > Is there a way to move the condition above into the find?
> > Essentially what I''m trying to achieve is:
> > A GearItem can contained 0..n GearItems and the GearItem->GearItem
> > relationship belongs to a list. So list 1 can have GearItem 1
> > containing GearItem 2 & 3 but list 2 can have GearItem 2
containing
> > GearItem 1 & 4, etc...
>
> In this case having all the conditions in the association probably
> isn''t the right thing to do since you''d have to have one
association
> per list and you''d have to figure out what to call them
>
> You could do this via an association proxy, eg
>
> has_many :contained_items, :through => :contained_gear_items do
>    def from_list(n)
>      find :all, :conditions => ["contained_gear_items.list_id =
?", n]
>    end
> end
>
> Then you can do stuff like foo.contained_items.from_list(23)
>
> Fred
>
>
>
> > On Apr 7, 9:02 am, Frederick Cheung
<frederick.che...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
> > wrote:
> >> On 7 Apr 2008, at 05:35, MaddyTheGoose wrote:
>
> >>> I''m having an issue with the data returning from a
self-referential
> >>> many-to-many relationship with an attribute in the join table
that''s
> >>> being used to limit the query. I''ll explain what
I''m doing below
> >>> which
> >>> will then bring you to the problem concerning the records
I''m
> >>> getting
> >>> back from the relationship.
>
> >> Your problem is only with the eager loading: when you load the has
> >> many through it does not use the already loaded contained_items to
> >> get
> >> the association, and so the conditions you specified at that point
do
> >> not apply. You probably want to specify the conditions on the
> >> association itself, although I''m not entirely sure what
you''re trying
> >> to do.
>
> >> Fred
>
> >>> MIGRATIONS (the two tables involved in the problem)
>
> >>> Note that in contained_gear_items there are three items
related to
> >>> gic[1] and list_id 1 and two other items related to gic[1] but
> >>> belong
> >>> to list_id 2 so I would think I wouldn''t see them
(considering I
> >>> have
> >>> ''contained_gear_items.list_id" => 1''
in the conditions - see below).
> >>> When looking at .contained_items the list_id = 1 constraint
seems to
> >>> have been missed. But if I go directly into the
contained_gear_items
> >>> join model I see only the three items, as I should. Any help
would
> >>> be
> >>> much appreciated.
>
> >>> MODELS
>
> >>> ## gear_item.rb (model)
> >>> class GearItem < ActiveRecord::Base
> >>> has_many :contained_gear_items
> >>> has_many :contained_items, :through =>
:contained_gear_items
>
> >>> ## contained_gear_item.rb (model)
> >>> class ContainedGearItem < ActiveRecord::Base
> >>> belongs_to :gear_item
> >>> belongs_to :contained_item, :class_name =>
''GearItem'',
> >>>   :foreign_key =>
''contained_gear_item_id''
>
> >>> IN THE SCRIPT/CONSOLE
>
> >>>>> gic = GearItem.find(
> >>> :all,
> >>> :include => "contained_gear_items",
> >>> :conditions => {"contained_gear_items.list_id"
=> 1, :is_container
> >>> => true},
> >>> :order => "contained_gear_items.position")
>
> >>>>> puts gic[1].contained_items
> >>> #<GearItem:0x3efeb80>
> >>> #<GearItem:0x3efeb30>
> >>> #<GearItem:0x3efeae0>
> >>> #<GearItem:0x3efea90>
> >>> #<GearItem:0x3efea40>
>
> >>>>> puts gic[1].contained_gear_items
> >>> #<ContainedGearItem:0x3f2c56c>
> >>> #<ContainedGearItem:0x3f29a4c>
> >>> #<ContainedGearItem:0x3f27328>
>
> >>> Thanks for any help you can provide...
>
> >>> Cheers
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