Rails - Jul 2006 - HABTM join table has an "ID" column - is this an issue?

All,

I''m building model objects for existing tables that I cannot modify.

In AWDWR, Dave says "Note that our join table has no id column...The 
second reason for not including an id column in the join table is that 
AR automatically includes all columns from the join tables when 
accessing rows using it.  If the join table included a column called id, 
its id would overwrite the id of the rows in the joined tables."

Unfortunately, my join table does have a column called id.  Is there a 
directive that can help me with this or some way to get around it per 
Dave Thomas''s quote above?

Thanks,
Wes

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Wes Gamble wrote:
> All,
> 
> I''m building model objects for existing tables that I cannot
modify.
> 
> In AWDWR, Dave says "Note that our join table has no id column...The 
> second reason for not including an id column in the join table is that 
> AR automatically includes all columns from the join tables when 
> accessing rows using it.  If the join table included a column called id, 
> its id would overwrite the id of the rows in the joined tables."
> 
> Unfortunately, my join table does have a column called id.  Is there a 
> directive that can help me with this or some way to get around it per 
> Dave Thomas''s quote above?
> 
> Thanks,
> Wes
Should I provide a value for the :select option, which will keep a 
SELECT * from happening on my join table?


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You could upgrade the join table to a full model and use has_many
:through in place of habtm.

On 7/5/06, Wes Gamble <weyus@att.net> wrote:
> Wes Gamble wrote:
> > All,
> >
> > I''m building model objects for existing tables that I cannot
modify.
> >
> > In AWDWR, Dave says "Note that our join table has no id
column...The
> > second reason for not including an id column in the join table is that
> > AR automatically includes all columns from the join tables when
> > accessing rows using it.  If the join table included a column called
id,
> > its id would overwrite the id of the rows in the joined tables."
> >
> > Unfortunately, my join table does have a column called id.  Is there a
> > directive that can help me with this or some way to get around it per
> > Dave Thomas''s quote above?
> >
> > Thanks,
> > Wes
>
> Should I provide a value for the :select option, which will keep a
> SELECT * from happening on my join table?
>
>
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> Rails mailing list
> Rails@lists.rubyonrails.org
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Tom Ward wrote:
> You could upgrade the join table to a full model and use has_many
> :through in place of habtm.
I just realized, however, that although my join table has an "id" 
column, neither of the join_ed_ tables on either side of the association 
have "id" columns.

So, I''m thinking that there shouldn''t be any collision between
columns
here.

Where can I find out more about has_many :through? - I''m unfamiliar
with
this option.

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On 7/5/06, Wes Gamble <weyus@att.net> wrote:
> Where can I find out more about has_many :through? - I''m
unfamiliar with
> this option.
http://api.rubyonrails.com/classes/ActiveRecord/Associations/ClassMethods.html#M000530

http://wiki.rubyonrails.org/rails/pages/ThroughAssociations

Tom

Wes Gamble wrote:
> Tom Ward wrote:
>> You could upgrade the join table to a full model and use has_many
>> :through in place of habtm.
> 
> I just realized, however, that although my join table has an "id"
> column, neither of the join_ed_ tables on either side of the association 
> have "id" columns.
> 
> So, I''m thinking that there shouldn''t be any collision
between columns
> here.
> 
> Where can I find out more about has_many :through? - I''m
unfamiliar with
> this option.
You shouldn''t have an "id" column in a join table - that will
just get
you in trouble. If you have anything in your join table besides the 
foreign_keys of the two tables being joined, you''ll have problems. In 
that case, you''ll want to use a join model (has_many :through) instead.

http://blog.hasmanythrough.com/articles/2006/04/20/many-to-many-dance-off

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

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Josh Susser wrote:
> Wes Gamble wrote:
>> Tom Ward wrote:
>>> You could upgrade the join table to a full model and use has_many
>>> :through in place of habtm.
>> 
>> I just realized, however, that although my join table has an
"id"
>> column, neither of the join_ed_ tables on either side of the
association
>> have "id" columns.
>> 
>> So, I''m thinking that there shouldn''t be any
collision between columns
>> here.
>> 
>> Where can I find out more about has_many :through? - I''m
unfamiliar with
>> this option.
> 
> You shouldn''t have an "id" column in a join table - that
will just get
> you in trouble. If you have anything in your join table besides the 
> foreign_keys of the two tables being joined, you''ll have problems.
In
> that case, you''ll want to use a join model (has_many :through)
instead.
> 
> http://blog.hasmanythrough.com/articles/2006/04/20/many-to-many-dance-off
> 
> --
> Josh Susser
> http://blog.hasmanythrough.com

Will I have problems if _neither_ of the two tables in the HABTM 
relationship has an "id" column?

WG

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Wes Gamble wrote:
> Will I have problems if _neither_ of the two tables in the HABTM 
> relationship has an "id" column?
ActiveRecord requires a primary key to manage object identity and to do 
joins between tables. If you have a primary key but have renamed the 
column from "id" to something else, you''ll be fine. If not,
you''ll need
to change something, or habtm won''t have anything to work with to do
the
joins.

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

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