Rails - Jul 2006 - Deleting join association of has_many :through

I''m trying to use has_many :through, since my join model deserves being
more than just an intersection table.

But when I try to break the association, the break only seems 
"temporary":

Let''s say my two tables are Users and Colors, and the join model is 
Favorites.

user = Users.find(1)
user.colors.length
>> 2
c = user.colors.first
>> #<Color:....>
user.colors.delete(c)
user.colors.length
>> 1
Now what do I do here to make this persist?

If I reload my page, user.colors.length == 2 again, and the old color is 
still a part of the collection.

I''ve tried reloading the collection after deleting, hoping that would 
refresh the associations:

user.colors(true)

but I get 2 again, not 1.

Any ideas?

(I know, I know, I''m a moron...)

Thanks
Jeff

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Jeff Cohen wrote on 10.07.2006 22:12:
> I''m trying to use has_many :through, since my join model deserves
being
[...]
> user.colors.length
>>> 2
> c = user.colors.first
>>> #<Color:....>
> 
> user.colors.delete(c)
> user.colors.length
>>> 1
> 
> Now what do I do here to make this persist?
> 
> If I reload my page, user.colors.length == 2 again, and the old color is 
> still a part of the collection.
I think there is a problem in your table relations.

:through: Specifies a Join Model to perform the query through. Options
for :class_name and :foreign_key are ignored, as the association uses
the source reflection. You can only use a :through query through a
belongs_to or has_many association.

Have you noticed the last sentence?

Markus Kolb wrote:
> 
> :through: Specifies a Join Model to perform the query through. Options
> for :class_name and :foreign_key are ignored, as the association uses
> the source reflection. You can only use a :through query through a
> belongs_to or has_many association.
> 
> Have you noticed the last sentence?
I think I''m doing it right.

class User
  has_many :favorites
  has_many :colors, :through => :favorites
end

class Color
  has_many :favorites
  has_many :users, :through => :favorites
end

class Favorite
  belongs_to :user
  belongs_to :color
end

Are you saying I''ve still got the relationships wrong somehow?

def delete_color
  color = Color.find(params[:color_id])
  user.colors.delete(color) # this works in script/console as expected
  # at this point, user.colors.length is correct
  redirect :action => :show # this will show 2 favorite colors again: 
user.colors.length is wrong
end


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> Are you saying I''ve still got the relationships wrong somehow?
>
> def delete_color
>   color = Color.find(params[:color_id])
>   user.colors.delete(color) # this works in script/console as expected
>   # at this point, user.colors.length is correct
>   redirect :action => :show # this will show 2 favorite colors again:
> user.colors.length is wrong
> end
>
You''ll want to delete the Favorite object that joins them.

user.favorites.find_by_color_id(params[:color_id]).destroy

-- 
Rick Olson
http://techno-weenie.net

Rick Olson wrote on 11.07.2006 00:34:
>> Are you saying I''ve still got the relationships wrong somehow?
>>
>> def delete_color
>>   color = Color.find(params[:color_id])
>>   user.colors.delete(color) # this works in script/console as expected
>>   # at this point, user.colors.length is correct
>>   redirect :action => :show # this will show 2 favorite colors
again:
>> user.colors.length is wrong
>> end
>>
> 
> You''ll want to delete the Favorite object that joins them.
> 
> user.favorites.find_by_color_id(params[:color_id]).destroy
> 
But it should be possible over colors collection, too.
Do you need a user.colors.save afterwards?

Markus Kolb wrote:
> Rick Olson wrote on 11.07.2006 00:34:
>> 
>> You''ll want to delete the Favorite object that joins them.
>> 
>> user.favorites.find_by_color_id(params[:color_id]).destroy
>> 
> 
> But it should be possible over colors collection, too.
> Do you need a user.colors.save afterwards?
user.colors.save isn''t possible (method missing), but that was a good 
clue.

user.save! does the trick.

Thanks Markus!

Jeff
softiesonrails.com




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Jeff Cohen wrote on 11.07.2006 03:33:
> Markus Kolb wrote:
>> Rick Olson wrote on 11.07.2006 00:34:
>>> You''ll want to delete the Favorite object that joins them.
>>>
>>> user.favorites.find_by_color_id(params[:color_id]).destroy
>>>
>> But it should be possible over colors collection, too.
>> Do you need a user.colors.save afterwards?
> 
> user.colors.save isn''t possible (method missing), but that was a
good
> clue.
> 
> user.save! does the trick.
Can you have a look in the log?
I''m interested in what SQL commands are executed on this save if only
colors association changed and no other user data.
Does it only update the association to colors or everything from user model?

Thanks
Markus

Hi,
i have a situation similar to this:

class User
  has_many :favorites
  has_many :colors, :through => :favorites
end

class Color
  has_many :favorites
  has_many :users, :through => :favorites
end

class Favorite
  belongs_to :user
  belongs_to :color
end


When i need to destroy a favorite association, i find it like this:
fav = user.favorites.find_by_color_id(color_id])

but i cannot destroy it:
calling "fav.destroy" raises a SQL error, because there is no ID field
in table Favorite.

How should that fav be deleted ?

Thanks,
Marcus

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On 7/21/06, Marcus Ob <mrqzzz@yahoo.it> wrote:
> Hi,
> i have a situation similar to this:
>
> class User
>   has_many :favorites
>   has_many :colors, :through => :favorites
> end
>
> class Color
>   has_many :favorites
>   has_many :users, :through => :favorites
> end
>
> class Favorite
>   belongs_to :user
>   belongs_to :color
> end
>
>
> When i need to destroy a favorite association, i find it like this:
> fav = user.favorites.find_by_color_id(color_id])
>
> but i cannot destroy it:
> calling "fav.destroy" raises a SQL error, because there is no ID
field
> in table Favorite.
>
> How should that fav be deleted ?
>
> Thanks,
> Marcus
>
> --
> Posted via http://www.ruby-forum.com/.
> _______________________________________________
> Rails mailing list
> Rails@lists.rubyonrails.org
> http://lists.rubyonrails.org/mailman/listinfo/rails
>
user.favorites.destroy_all(["color_id=?", color_id])

Marcus Ob wrote:
> Hi,
> i have a situation similar to this:
> 
> class User
>   has_many :favorites
>   has_many :colors, :through => :favorites
> end
> 
> class Color
>   has_many :favorites
>   has_many :users, :through => :favorites
> end
> 
> class Favorite
>   belongs_to :user
>   belongs_to :color
> end
> 
> 
> When i need to destroy a favorite association, i find it like this:
> fav = user.favorites.find_by_color_id(color_id])
> 
> but i cannot destroy it:
> calling "fav.destroy" raises a SQL error, because there is no ID
field
> in table Favorite.
> 
> How should that fav be deleted ?
If you have no :id field, then your join model is broken. You need an 
:id in favorites for has_many :through to work right.

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

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Pat Maddox wrote:
> On 7/21/06, Marcus Ob <mrqzzz@yahoo.it> wrote:
>>   has_many :users, :through => :favorites
>>
>> Posted via http://www.ruby-forum.com/.
>> _______________________________________________
>> Rails mailing list
>> Rails@lists.rubyonrails.org
>> http://lists.rubyonrails.org/mailman/listinfo/rails
>>
> 
> user.favorites.destroy_all(["color_id=?", color_id])

Thank you, but it''s not working:

I tried
user.favorites.destroy_all(["color_id=?", color_id])
But it raises an error:
"wrong number of arguments (1 for 0)".

Without arguments, it wont complain
user.favorites.destroy_all
But i get an error because there is no ID column:
Mysql::Error: #42S22Unknown column ''id'' in ''where
clause'': DELETE FROM
favorites WHERE id = NULL

The only thing working is
user.colors.clear
which deletes all favorite colors of user, but i don''t want to clear 
*all* records, only a specific one.

Any other ideas?
Thanks,
Marcus.

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Josh Susser wrote:
> Marcus Ob wrote:
>> Hi,
>> i have a situation similar to this:
>> 
>> class User
>>   has_many :favorites
>>   has_many :colors, :through => :favorites
>> end
>> 
>> class Color
>>   has_many :favorites
>>   has_many :users, :through => :favorites
>> end
>> 
>> class Favorite
>>   belongs_to :user
>>   belongs_to :color
>> end
>> 
>> 
>> When i need to destroy a favorite association, i find it like this:
>> fav = user.favorites.find_by_color_id(color_id])
>> 
>> but i cannot destroy it:
>> calling "fav.destroy" raises a SQL error, because there is no
ID field
>> in table Favorite.
>> 
>> How should that fav be deleted ?
> 
> If you have no :id field, then your join model is broken. You need an 
> :id in favorites for has_many :through to work right.
> 
> --
> Josh Susser
> http://blog.hasmanythrough.com

I have id fields in both master tables (users and colors) and the join 
table (favorites) has a pk composed by the two fields user_id+color_id

Is that wrong?
Thanks,
Marcus.

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On 7/21/06, Marcus Ob <mrqzzz@yahoo.it> wrote:
> Pat Maddox wrote:
> > On 7/21/06, Marcus Ob <mrqzzz@yahoo.it> wrote:
> > user.favorites.destroy_all(["color_id=?", color_id])
>
>
> Thank you, but it''s not working
Sorry, it should be delete_all

As far as using composite primary keys...don''t.  Sounds like
you''re
creating a rails app from scratch, so there''s no reason at all you
should be using them.

Pat

Pat Maddox wrote:
> On 7/21/06, Marcus Ob <mrqzzz@yahoo.it> wrote:
>> Pat Maddox wrote:
>> > On 7/21/06, Marcus Ob <mrqzzz@yahoo.it> wrote:
>> > user.favorites.destroy_all(["color_id=?", color_id])
>>
>>
>> Thank you, but it''s not working
> 
> Sorry, it should be delete_all
> 
> As far as using composite primary keys...don''t.  Sounds like
you''re
> creating a rails app from scratch, so there''s no reason at all you
> should be using them.
> 
> Pat
So using has_many_through, should i use set the pk to an id field for 
table "favorites", and leave color_id and user_id as fk ?

I was using a composite pk color_id+user_id in favorites table because 
it was explained to do so for HABTM.

Thanks,
Marcus.

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On 7/21/06, Marcus Ob <mrqzzz@yahoo.it> wrote:
> Pat Maddox wrote:
> > On 7/21/06, Marcus Ob <mrqzzz@yahoo.it> wrote:
> >> Pat Maddox wrote:
> >> > On 7/21/06, Marcus Ob <mrqzzz@yahoo.it> wrote:
> >> > user.favorites.destroy_all(["color_id=?",
color_id])
> >>
> >>
> >> Thank you, but it''s not working
> >
> > Sorry, it should be delete_all
> >
> > As far as using composite primary keys...don''t.  Sounds like
you''re
> > creating a rails app from scratch, so there''s no reason at
all you
> > should be using them.
> >
> > Pat
>
> So using has_many_through, should i use set the pk to an id field for
> table "favorites", and leave color_id and user_id as fk ?
Yes.

You will also probably want to make a multicolumn index on color_id
and user_id for performance reasons.  This is really a secondary
concern though and you shouldn''t do that until you see how
you''re
actually using the table.

Pat

Pat Maddox wrote:
> On 7/21/06, Marcus Ob <mrqzzz@yahoo.it> wrote:
>> >
>> > As far as using composite primary keys...don''t.  Sounds
like you''re
>> > creating a rails app from scratch, so there''s no reason
at all you
>> > should be using them.
>> >
>> > Pat
>>
>> So using has_many_through, should i use set the pk to an id field for
>> table "favorites", and leave color_id and user_id as fk ?
> 
> Yes.
> 
> You will also probably want to make a multicolumn index on color_id
> and user_id for performance reasons.  This is really a secondary
> concern though and you shouldn''t do that until you see how
you''re
> actually using the table.
> 
> Pat
Pat (and Josh), thank you very much, that solved my
user.favorites.find_by_color_id(color_id).destroy

I am still stuck in the
user.favorites << Color.find_by_id(some_id)
user.save
which does not save any record.

Any suggestions?
Thanks for the great help.
Marcus.

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On 7/21/06, Marcus Ob <mrqzzz@yahoo.it> wrote:
> Pat Maddox wrote:
> > On 7/21/06, Marcus Ob <mrqzzz@yahoo.it> wrote:
> >> >
> >> > As far as using composite primary keys...don''t. 
Sounds like you''re
> >> > creating a rails app from scratch, so there''s no
reason at all you
> >> > should be using them.
> >> >
> >> > Pat
> >>
> >> So using has_many_through, should i use set the pk to an id field
for
> >> table "favorites", and leave color_id and user_id as fk
?
> >
> > Yes.
> >
> > You will also probably want to make a multicolumn index on color_id
> > and user_id for performance reasons.  This is really a secondary
> > concern though and you shouldn''t do that until you see how
you''re
> > actually using the table.
> >
> > Pat
>
> Pat (and Josh), thank you very much, that solved my
> user.favorites.find_by_color_id(color_id).destroy
>
> I am still stuck in the
> user.favorites << Color.find_by_id(some_id)
> user.save
> which does not save any record.
>
> Any suggestions?
> Thanks for the great help.
> Marcus.
>
> --
> Posted via http://www.ruby-forum.com/.
> _______________________________________________
> Rails mailing list
> Rails@lists.rubyonrails.org
> http://lists.rubyonrails.org/mailman/listinfo/rails
>
disclaimer: I still haven''t used has_many :through yet.  Maybe the
code you showed is supposed to work, I''m not sure.

Anyway, it ought to be
user.favorites << Favorite.new(:color => Color.find(some_id))

If you''re just creating the favorite at that point in time and
won''t
be using the favorites method, you should just do
Favorite.create(:user => user, :color => Color.find(some_id))

You might be able to do
user.colors << Color.find(some_id)

but again, since that would rely on has_many :through, I''m not sure.

Pat

Marcus Ob wrote:
> Pat (and Josh), thank you very much, that solved my
> user.favorites.find_by_color_id(color_id).destroy
All tables in Rails except for habtm need a single column pk. You can 
create indexes as you will, but the pk must be a single column, and if 
you can go with the default of an auto-inc int named :id things will be 
much easier for you.
> I am still stuck in the
> user.favorites << Color.find_by_id(some_id)
> user.save
> which does not save any record.
That''s just the way has_many :through is.  Read this:
http://blog.hasmanythrough.com/articles/2006/04/17/join-models-not-proxy-collections

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

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Josh Susser wrote:
> Marcus Ob wrote:
>> Pat (and Josh), thank you very much, that solved my
>> user.favorites.find_by_color_id(color_id).destroy
> 
> All tables in Rails except for habtm need a single column pk. You can 
> create indexes as you will, but the pk must be a single column, and if 
> you can go with the default of an auto-inc int named :id things will be 
> much easier for you.
> 
>> I am still stuck in the
>> user.favorites << Color.find_by_id(some_id)
>> user.save
>> which does not save any record.
> 
> That''s just the way has_many :through is.  Read this:
>
http://blog.hasmanythrough.com/articles/2006/04/17/join-models-not-proxy-collections
> 
> --
> Josh Susser
> http://blog.hasmanythrough.com
I see, thank you Josh.
And thank you Pat.
I guess perhaps this is the code to add a new favorite:

fav=Favorite.new(:user_id=>user.id, :color_id=>some_color.id)
fav.save

Best regards,
Marcus.

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