Rails - Mar 2010 - how I do different has_and_belongs_to_many for the same model?

Hi,

I have a team which has and belongs to many players.

class Team < ActiveRecord::Base
  has_and_belongs_to_many :players
end

class Player < ActiveRecord::Base
  has_and_belongs_to_many :teams
end

What I''d like to do is add bench players to my team.  The bench will
have many players and many players can be on the bench.

I tried to do it like this:

class Team < ActiveRecord::Base
  has_and_belongs_to_many :players
  has_and_belongs_to_many :bench_players, :class =>
''Player''
end

I made the association table like this:

class TeamsBenchPlayers < ActiveRecord::Migration
  def self.up
    create_table :teams_bench_players, :id => false do |t|
      t.column :team_id, :integer, :null => false
      t.column :player_id, :integer, :null => false
    end
    add_index :teams_bench_players, [:team_id]
    add_index :teams_bench_players, [:player_id]
  end
  def self.down
    drop_table :teams_bench_players
  end
end

However when I do this:

team.bench_players << player

It saves it in the wrong table, i.e. the team_players table.  What am
I doing wrong?

Thanks,
Frank

-- 
You received this message because you are subscribed to the Google Groups
"Ruby on Rails: Talk" group.
To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org
To unsubscribe from this group, send email to
rubyonrails-talk+unsubscribe-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org
For more options, visit this group at
http://groups.google.com/group/rubyonrails-talk?hl=en.

On Mar 2, 5:47 am, Frank Kim
<railso...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
> However when I do this:
>
> team.bench_players << player
>
> It saves it in the wrong table, i.e. the team_players table.  What am
> I doing wrong?
You need to tell activerecord to use a different join table (with
the :join_table) option

Fred
>
> Thanks,
> Frank
-- 
You received this message because you are subscribed to the Google Groups
"Ruby on Rails: Talk" group.
To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org
To unsubscribe from this group, send email to
rubyonrails-talk+unsubscribe@googlegroups.com.
For more options, visit this group at
http://groups.google.com/group/rubyonrails-talk?hl=en.

Some might argue that being on the bench or not is simply an attribute 
of a player... benched or playing, the player is still on the team.
-- 
Posted via http://www.ruby-forum.com/.

-- 
You received this message because you are subscribed to the Google Groups
"Ruby on Rails: Talk" group.
To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org
To unsubscribe from this group, send email to
rubyonrails-talk+unsubscribe-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org
For more options, visit this group at
http://groups.google.com/group/rubyonrails-talk?hl=en.

Thanks Frederick, I forgot about that option.

On Tue, Mar 2, 2010 at 3:00 AM, Frederick Cheung
<frederick.cheung-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:
>
>
> On Mar 2, 5:47 am, Frank Kim
<railso...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
>
>> However when I do this:
>>
>> team.bench_players << player
>>
>> It saves it in the wrong table, i.e. the team_players table.  What am
>> I doing wrong?
>
> You need to tell activerecord to use a different join table (with
> the :join_table) option
>
> Fred
>>
>> Thanks,
>> Frank
>
> --
> You received this message because you are subscribed to the Google Groups
"Ruby on Rails: Talk" group.
> To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org
> To unsubscribe from this group, send email to
rubyonrails-talk+unsubscribe@googlegroups.com.
> For more options, visit this group at
http://groups.google.com/group/rubyonrails-talk?hl=en.
>
>


-- 
Frank Kim
http://betweengo.com/

-- 
You received this message because you are subscribed to the Google Groups
"Ruby on Rails: Talk" group.
To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org
To unsubscribe from this group, send email to
rubyonrails-talk+unsubscribe@googlegroups.com.
For more options, visit this group at
http://groups.google.com/group/rubyonrails-talk?hl=en.

Hi Ar,
The attribute idea makes a lot of sense.  If I did it that way then I
could use the same join table.  However I would have to use specify
custom SQL for how to select from it, right?  Or is there a better
way?
-Frank

On Tue, Mar 2, 2010 at 5:58 AM, Ar Chron
<lists-fsXkhYbjdPsEEoCn2XhGlw@public.gmane.org>
wrote:
> Some might argue that being on the bench or not is simply an attribute
> of a player... benched or playing, the player is still on the team.
> --
> Posted via http://www.ruby-forum.com/.
>
> --
> You received this message because you are subscribed to the Google Groups
"Ruby on Rails: Talk" group.
> To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org
> To unsubscribe from this group, send email to
rubyonrails-talk+unsubscribe-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org
> For more options, visit this group at
http://groups.google.com/group/rubyonrails-talk?hl=en.
>
>


-- 
Frank Kim
http://betweengo.com/

-- 
You received this message because you are subscribed to the Google Groups
"Ruby on Rails: Talk" group.
To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org
To unsubscribe from this group, send email to
rubyonrails-talk+unsubscribe-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org
For more options, visit this group at
http://groups.google.com/group/rubyonrails-talk?hl=en.

Frank Kim wrote:
> Hi Ar,
> The attribute idea makes a lot of sense.  If I did it that way then I
> could use the same join table.  However I would have to use specify
> custom SQL for how to select from it, right?  Or is there a better
> way?
You could just have "benched" be a boolean field in the database. If 
it''s true, the player''s on the bench. If it''s false,
he''s on the field.
Then you can do this:

player = Player.find_by_last_name "Ronaldo"
player.benched = true # Be a team player, Ronaldo!
-- 
Posted via http://www.ruby-forum.com/.

-- 
You received this message because you are subscribed to the Google Groups
"Ruby on Rails: Talk" group.
To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org
To unsubscribe from this group, send email to
rubyonrails-talk+unsubscribe-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org
For more options, visit this group at
http://groups.google.com/group/rubyonrails-talk?hl=en.

Not sure if has_and_belongs_to_many is exactly right (can a player be
on more than one team?) but one option is to add :conditions to the
declarations:

has_and_belongs_to_many :benched_players, :join_table =>
''teams_players'', :association_foreign_key =>
''player_id'', :class_name
=> ''Player'', :conditions => { :benched => true }

(not sure if this is 100% of what you need, but you get the idea)

On the other hand, if a player really can only be on one team, you''ll
have a much better time if you switch back to a plain has_many. On the
other hand, if you''ve got a situation where players *can* be on
multiple teams, it''s possible that they could be "benched"
only on
some of them; in that case, you''ll want a "decorated join
model", with
has_many :through.

--Matt Jones


On Mar 2, 9:04 am, Frank Kim
<railso...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:
> Hi Ar,
> The attribute idea makes a lot of sense.  If I did it that way then I
> could use the same join table.  However I would have to use specify
> custom SQL for how to select from it, right?  Or is there a better
> way?
> -Frank
-- 
You received this message because you are subscribed to the Google Groups
"Ruby on Rails: Talk" group.
To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org
To unsubscribe from this group, send email to
rubyonrails-talk+unsubscribe@googlegroups.com.
For more options, visit this group at
http://groups.google.com/group/rubyonrails-talk?hl=en.

The attribute (Matt Jones calls it a "condition") of being on the
bench or
not on the bench is a property of the player not the team.

A team does not belong to the players. Players make up the team.

Consider the deletion anomaly. If a Player is removed, does the team cease
to exist?

However, If a team is removed, then none of the players can theoretically
belong to that team.



On 2 March 2010 13:51, Matt Jones
<al2o3cr-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
> Not sure if has_and_belongs_to_many is exactly right (can a player be
> on more than one team?) but one option is to add :conditions to the
> declarations:
>
> has_and_belongs_to_many :benched_players, :join_table =>
> ''teams_players'', :association_foreign_key =>
''player_id'', :class_name
> => ''Player'', :conditions => { :benched => true }
>
> (not sure if this is 100% of what you need, but you get the idea)
>
> On the other hand, if a player really can only be on one team,
you''ll
> have a much better time if you switch back to a plain has_many. On the
> other hand, if you''ve got a situation where players *can* be on
> multiple teams, it''s possible that they could be
"benched" only on
> some of them; in that case, you''ll want a "decorated join
model", with
> has_many :through.
>
> --Matt Jones
>
>
> On Mar 2, 9:04 am, Frank Kim
<railso...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
> > Hi Ar,
> > The attribute idea makes a lot of sense.  If I did it that way then I
> > could use the same join table.  However I would have to use specify
> > custom SQL for how to select from it, right?  Or is there a better
> > way?
> > -Frank
>
> --
> You received this message because you are subscribed to the Google Groups
> "Ruby on Rails: Talk" group.
> To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org
> To unsubscribe from this group, send email to
>
rubyonrails-talk+unsubscribe-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org<rubyonrails-talk%2Bunsubscribe-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org>
> .
> For more options, visit this group at
> http://groups.google.com/group/rubyonrails-talk?hl=en.
>
>

-- 
Charles A. Lopez
charlesalopez-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org

What''s your vision for your organization?
What''s your biggest challenge?

Let''s talk.
(IBM Partner)

-- 
You received this message because you are subscribed to the Google Groups
"Ruby on Rails: Talk" group.
To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org
To unsubscribe from this group, send email to
rubyonrails-talk+unsubscribe-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org
For more options, visit this group at
http://groups.google.com/group/rubyonrails-talk?hl=en.

That makes a lot of sense Ar.  Thanks!

On Tue, Mar 2, 2010 at 6:22 AM, Aldric Giacomoni
<lists-fsXkhYbjdPsEEoCn2XhGlw@public.gmane.org>
wrote:
> Frank Kim wrote:
>> Hi Ar,
>> The attribute idea makes a lot of sense.  If I did it that way then I
>> could use the same join table.  However I would have to use specify
>> custom SQL for how to select from it, right?  Or is there a better
>> way?
>
> You could just have "benched" be a boolean field in the database.
If
> it''s true, the player''s on the bench. If it''s
false, he''s on the field.
> Then you can do this:
>
> player = Player.find_by_last_name "Ronaldo"
> player.benched = true # Be a team player, Ronaldo!
> --
> Posted via http://www.ruby-forum.com/.
>
> --
> You received this message because you are subscribed to the Google Groups
"Ruby on Rails: Talk" group.
> To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org
> To unsubscribe from this group, send email to
rubyonrails-talk+unsubscribe@googlegroups.com.
> For more options, visit this group at
http://groups.google.com/group/rubyonrails-talk?hl=en.
>
>


-- 
Frank Kim
http://betweengo.com/

-- 
You received this message because you are subscribed to the Google Groups
"Ruby on Rails: Talk" group.
To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org
To unsubscribe from this group, send email to
rubyonrails-talk+unsubscribe@googlegroups.com.
For more options, visit this group at
http://groups.google.com/group/rubyonrails-talk?hl=en.

Hi Ar,
Actually I realized this won''t work because players can be on multiple
teams and can be benched on one team but not the other.  Therefore it
can''t be an attribute of the player, it has to be an attribute of the
team.
Looks like I''ll have to go back to my old idea.
-Frank

On Tue, Mar 2, 2010 at 6:22 AM, Aldric Giacomoni
<lists-fsXkhYbjdPsEEoCn2XhGlw@public.gmane.org>
wrote:
> Frank Kim wrote:
>> Hi Ar,
>> The attribute idea makes a lot of sense.  If I did it that way then I
>> could use the same join table.  However I would have to use specify
>> custom SQL for how to select from it, right?  Or is there a better
>> way?
>
> You could just have "benched" be a boolean field in the database.
If
> it''s true, the player''s on the bench. If it''s
false, he''s on the field.
> Then you can do this:
>
> player = Player.find_by_last_name "Ronaldo"
> player.benched = true # Be a team player, Ronaldo!
> --
> Posted via http://www.ruby-forum.com/.
>
> --
> You received this message because you are subscribed to the Google Groups
"Ruby on Rails: Talk" group.
> To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org
> To unsubscribe from this group, send email to
rubyonrails-talk+unsubscribe@googlegroups.com.
> For more options, visit this group at
http://groups.google.com/group/rubyonrails-talk?hl=en.
>
>


-- 
Frank Kim
http://betweengo.com/

-- 
You received this message because you are subscribed to the Google Groups
"Ruby on Rails: Talk" group.
To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org
To unsubscribe from this group, send email to
rubyonrails-talk+unsubscribe@googlegroups.com.
For more options, visit this group at
http://groups.google.com/group/rubyonrails-talk?hl=en.

Frederick,
That was the solution.
Thanks!
-Frank

On Tue, Mar 2, 2010 at 6:01 AM, Frank Kim
<railsonly-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:
> Thanks Frederick, I forgot about that option.
>
> On Tue, Mar 2, 2010 at 3:00 AM, Frederick Cheung
> <frederick.cheung-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
>>
>>
>> On Mar 2, 5:47 am, Frank Kim
<railso...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
>>
>>> However when I do this:
>>>
>>> team.bench_players << player
>>>
>>> It saves it in the wrong table, i.e. the team_players table.  What
am
>>> I doing wrong?
>>
>> You need to tell activerecord to use a different join table (with
>> the :join_table) option
>>
>> Fred
>>>
>>> Thanks,
>>> Frank
>>
>> --
>> You received this message because you are subscribed to the Google
Groups "Ruby on Rails: Talk" group.
>> To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org
>> To unsubscribe from this group, send email to
rubyonrails-talk+unsubscribe-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org
>> For more options, visit this group at
http://groups.google.com/group/rubyonrails-talk?hl=en.
>>
>>
>
>
>
> --
> Frank Kim
> http://betweengo.com/
>


-- 
Frank Kim
http://betweengo.com/

-- 
You received this message because you are subscribed to the Google Groups
"Ruby on Rails: Talk" group.
To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org
To unsubscribe from this group, send email to
rubyonrails-talk+unsubscribe@googlegroups.com.
For more options, visit this group at
http://groups.google.com/group/rubyonrails-talk?hl=en.