Rails - Mar 2009 - how to retrieve single record through chained associations

Hi

I have a standard associations belongs_to, has_many  :through


class Shop < ActiveRecord::Base
  has_many :show_categories
  has_many :categories, :through => :shop_categories
end

class Category < ActiveRecord::Base
  has_many :shop_categories
  has_many :shops, :through => :shop_categories
end

class ShopCategory < ActiveRecord::Base
  belongs_to :shop
  belongs_to :category
end

There is one root category with hierarchical data for shops.
shop_categories are holding some common fields for shop and category.
mixed one record for one shop and category. So, for 100 categories, in
shop_categories are 200 records, one for each shop.

For this example I have 2 shops.

Shop.first.category.find(10).shop_categories Rails are returning 2
shop_categories records one for each shop. Something is wrong with
associations because it should find in shop_categories all records for
first shop.

What I need is to retrieve only one record from shop_categories for
corresponding association.
I have tried has_one :shop_category but it returns not one but first and
always same never less if I try
Shop.find(1).category.find(10).shop_categories or
Shop.find(2).category.find(10).shop_categories

So, what is really happening with this association?
I realy can not guess, and I have tried all sort of things with no
results.

Logically this kind of chaining
Shop.find(2).category.find(10).shop_categories should collect and join
appropriate associations and return data only for shop 2.

Could any one give some clues? Or clarify this kind of relation. Maybe
there is another way to retrieve this single data?


Thanks,
Tod
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Hi Tod

For finding the category 10 of shop 1, the following should work by using
Activerecord associations

Shop.find(1).categories.find(10)
or 
Shop.find(1).categories.find(:first, :conditions => ''category =
10'')

rainer




Dharmdip Rathod wrote:
> 
> 
> Hi
> 
> I have a standard associations belongs_to, has_many  :through
> 
> 
> class Shop < ActiveRecord::Base
>   has_many :show_categories
>   has_many :categories, :through => :shop_categories
> end
> 
> class Category < ActiveRecord::Base
>   has_many :shop_categories
>   has_many :shops, :through => :shop_categories
> end
> 
> class ShopCategory < ActiveRecord::Base
>   belongs_to :shop
>   belongs_to :category
> end
> 
> There is one root category with hierarchical data for shops.
> shop_categories are holding some common fields for shop and category.
> mixed one record for one shop and category. So, for 100 categories, in
> shop_categories are 200 records, one for each shop.
> 
> For this example I have 2 shops.
> 
> Shop.first.category.find(10).shop_categories Rails are returning 2
> shop_categories records one for each shop. Something is wrong with
> associations because it should find in shop_categories all records for
> first shop.
> 
> What I need is to retrieve only one record from shop_categories for
> corresponding association.
> I have tried has_one :shop_category but it returns not one but first and
> always same never less if I try
> Shop.find(1).category.find(10).shop_categories or
> Shop.find(2).category.find(10).shop_categories
> 
> So, what is really happening with this association?
> I realy can not guess, and I have tried all sort of things with no
> results.
> 
> Logically this kind of chaining
> Shop.find(2).category.find(10).shop_categories should collect and join
> appropriate associations and return data only for shop 2.
> 
> Could any one give some clues? Or clarify this kind of relation. Maybe
> there is another way to retrieve this single data?
> 
> 
> Thanks,
> Tod
> -- 
> Posted via http://www.ruby-forum.com/.
> 
> > 
> 
> 
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On Mar 7, 4:39 pm, Tod Tod
<rails-mailing-l...-ARtvInVfO7ksV2N9l4h3zg@public.gmane.org>
wrote:
>
> Logically this kind of chaining
> Shop.find(2).category.find(10).shop_categories should collect and join
> appropriate associations and return data only for shop 2.
That''''s not really how it works - once you do that find(10)
you get a
perfectly ordinary instance of Category (ie the stop_categories is
just scoped to the category - not the shop.

I''m not sure why you''re doing this at all - why not Shop.find
(2).shop_categories.find_by_category_id(10) (or
find_all_by_category_id if you want all of them)

Fred
>
> Could any one give some clues? Or clarify this kind of relation. Maybe
> there is another way to retrieve this single data?
>
> Thanks,
> Tod
> --
> Posted viahttp://www.ruby-forum.com/.
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Hi rainer54

Actually

Shop.find(1).categories.find(10) and
Shop.find(1).categories.find(:first, :conditions => ''category_id =
10'')

are the different ways to retrieve same category record in association 
with shop 1.

But going further with association I need to retrieve records from 
shop_categories, so doing this

Shop.find(1).category.find(10).shop_categories

returns two records associated to two shops and category #10 from 
shop_categories. And no matter if I try Shop.find(1).... or
Shop.find(2)..... it gives me same results from shop_categories.

I need to use Rails 2.1 but I don''t think so that is some problem from 
within Rails.


Tod


rainer54 wrote:
> Hi Tod
> 
> For finding the category 10 of shop 1, the following should work by 
> using
> Activerecord associations
> 
> Shop.find(1).categories.find(10)
> or
> Shop.find(1).categories.find(:first, :conditions => ''category =
10'')
> 
> rainer
> 
> 
> 
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Hi Frederick

Thanks for answer.

I''m just trying to investigate why it is not chained whole over all 
associations. I think that each association shuold act as maybe proxy 
and pass from begining Shop.find(1) till the end of this chainings and 
pass Shop record.

It sounds to me naturally way of living this kind of chainging. But I is 
it is not.

I''m just guessing but I think this kind of behaviour is in DataMapper, 
am I right?


Tod




Frederick Cheung wrote:
> On Mar 7, 4:39�pm, Tod Tod
<rails-mailing-l...-ARtvInVfO7ksV2N9l4h3zg@public.gmane.org> wrote:
>>
>> Logically this kind of chaining
>> Shop.find(2).category.find(10).shop_categories should collect and join
>> appropriate associations and return data only for shop 2.
> 
> That''''s not really how it works - once you do that
find(10) you get a
> perfectly ordinary instance of Category (ie the stop_categories is
> just scoped to the category - not the shop.
> 
> I''m not sure why you''re doing this at all - why not
Shop.find
> (2).shop_categories.find_by_category_id(10) (or
> find_all_by_category_id if you want all of them)
> 
> Fred
-- 
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ok - misunderstood this

The solution is already given by Fred



On 7 Mrz., 19:01, Tod Tod
<rails-mailing-l...-ARtvInVfO7ksV2N9l4h3zg@public.gmane.org>
wrote:
> Hi rainer54
>
> Actually
>
> Shop.find(1).categories.find(10) and
> Shop.find(1).categories.find(:first, :conditions =>
''category_id = 10'')
>
> are the different ways to retrieve same category record in association
> with shop 1.
>
> But going further with association I need to retrieve records from
> shop_categories, so doing this
>
> Shop.find(1).category.find(10).shop_categories
>
> returns two records associated to two shops and category #10 from
> shop_categories. And no matter if I try Shop.find(1).... or
> Shop.find(2)..... it gives me same results from shop_categories.
>
> I need to use Rails 2.1 but I don''t think so that is some problem
from
> within Rails.
>
> Tod
>
> rainer54 wrote:
> > Hi Tod
>
> > For finding the category 10 of shop 1, the following should work by
> > using
> > Activerecord associations
>
> > Shop.find(1).categories.find(10)
> > or
> > Shop.find(1).categories.find(:first, :conditions =>
''category = 10'')
>
> > rainer
>
> --
> Posted viahttp://www.ruby-forum.com/.
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can u tell me online tutorial..???

On Mar 7, 10:55 pm, Frederick Cheung
<frederick.che...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:
> On Mar 7, 4:39 pm, Tod Tod
<rails-mailing-l...-ARtvInVfO7ksV2N9l4h3zg@public.gmane.org> wrote:
>
>
>
> > Logically this kind of chaining
> > Shop.find(2).category.find(10).shop_categories should collect and join
> > appropriate associations and return data only for shop 2.
>
> That''''s not really how it works - once you do that
find(10) you get a
> perfectly ordinary instance of Category (ie the stop_categories is
> just scoped to the category - not the shop.
>
> I''m not sure why you''re doing this at all - why not
Shop.find
> (2).shop_categories.find_by_category_id(10) (or
> find_all_by_category_id if you want all of them)
>
> Fred
>
>
>
>
>
> > Could any one give some clues? Or clarify this kind of relation. Maybe
> > there is another way to retrieve this single data?
>
> > Thanks,
> > Tod
> > --
> > Posted viahttp://www.ruby-forum.com/.- Hide quoted text -
>
> - Show quoted text -
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On Mar 7, 6:08 pm, Tod Tod
<rails-mailing-l...-ARtvInVfO7ksV2N9l4h3zg@public.gmane.org>
wrote:
>
> I''m just trying to investigate why it is not chained whole over
all
> associations. I think that each association shuold act as maybe proxy
> and pass from begining Shop.find(1) till the end of this chainings and
> pass Shop record.
>
> It sounds to me naturally way of living this kind of chainging. But I is
> it is not.
>
> I''m just guessing but I think this kind of behaviour is in
DataMapper,
> am I right?
>
don''t know about DataMapper. In activerecord as soon as you call find
you''ll get a normal record/array of records. if you just want
something that adds some extra conditions then you may be interested
in named_scope. The other thing is that (in active record) scopes
scope a particular table, so when you do Shop.find(1).categories then
the categories proxy there is scoping finds on Category to those with
the appropriate shop_id - it''s not magic thing across everything with
a shop_id column.

Fred


Fred


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Hi and thanks,

yes this works Shop.find(2).shop_categories.find_by_category_id(10)

In shop_categories table I have field ''active'' to mark that a
category
is visible/active for the shop.

So what is the best way to retrieve this value for shop''s category?

In Category model I have defined ''active'' so I can fetch with 
@category.active or
@categories.each do |category|
<%= category.name %>
<%= category.active %>
end


  def active
    self.merchant_categories.find_by_category_id(id).active
  end

I know that this is not so good solution, but I could not figured out 
over way to get this value. It is realy over kill for server. And It 
would get harder  if there are more values that I need to keep in 
merchant_categories.

Is there a better way to do it?


Tod





Frederick Cheung wrote:
> On Mar 7, 6:08�pm, Tod Tod
<rails-mailing-l...-ARtvInVfO7ksV2N9l4h3zg@public.gmane.org> wrote:
>> am I right?
>>
> don''t know about DataMapper. In activerecord as soon as you call
find
> you''ll get a normal record/array of records. if you just want
> something that adds some extra conditions then you may be interested
> in named_scope. The other thing is that (in active record) scopes
> scope a particular table, so when you do Shop.find(1).categories then
> the categories proxy there is scoping finds on Category to those with
> the appropriate shop_id - it''s not magic thing across everything
with
> a shop_id column.
> 
> Fred
> 
> 
> Fred
-- 
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> I know that this is not so good solution, but I could not figured out 
> over way to get this value. It is realy over kill for server. And It 
> would get harder  if there are more values that I need to keep in 
> merchant_categories.
oops, should be shop_categories

Tod

ps. hmm, here posts don''t have ''edit'' option
-- 
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Hi,

I see that nobody knows how to do better way.

So maybe someone could suggest different model design that I can do
@category.active

And just to avoid calling this 
self.merchant_categories.find_by_category_id(id).active

def active
  self.merchant_categories.find_by_category_id(id).active
end

instead to call
self.merchant_category.active


Thanks,
Tod




Tod Tod wrote:
> Hi and thanks,
> 
> yes this works Shop.find(2).shop_categories.find_by_category_id(10)
> 
> In shop_categories table I have field ''active'' to mark
that a category
> is visible/active for the shop.
> 
> So what is the best way to retrieve this value for shop''s
category?
> 
> In Category model I have defined ''active'' so I can fetch
with
> @category.active or
> @categories.each do |category|
> <%= category.name %>
> <%= category.active %>
> end
> 
> 
>   def active
>     self.merchant_categories.find_by_category_id(id).active
>   end
> 
> I know that this is not so good solution, but I could not figured out 
> over way to get this value. It is realy over kill for server. And It 
> would get harder  if there are more values that I need to keep in 
> merchant_categories.
> 
> Is there a better way to do it?
> 
> 
> Tod
> 
> 
> 
> 
> 
> Frederick Cheung wrote:
>> On Mar 7, 6:08�pm, Tod Tod
<rails-mailing-l...-ARtvInVfO7ksV2N9l4h3zg@public.gmane.org> wrote:
>>> am I right?
>>>
>> don''t know about DataMapper. In activerecord as soon as you
call find
>> you''ll get a normal record/array of records. if you just want
>> something that adds some extra conditions then you may be interested
>> in named_scope. The other thing is that (in active record) scopes
>> scope a particular table, so when you do Shop.find(1).categories then
>> the categories proxy there is scoping finds on Category to those with
>> the appropriate shop_id - it''s not magic thing across
everything with
>> a shop_id column.
>> 
>> Fred
>> 
>> 
>> Fred
-- 
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