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Frew Schmidt

2007-Jul-17 02:56 UTC

habtm confusion

Hello friends!

I am trying to make a database that will have a group of people set to
committees, and a person can be in multiple committees, and a committee
obviously has multiple people.  The people are senators at my
university.  These are my current models:

senator.rb:
--
class Senator < ActiveRecord::Base
  validates_presence_of :first_name, :last_name, :floor
  has_and_belongs_to_many :committees#, :dependent => :nullify
  #has_many :chairs, :class_name => "Committee"#, :dependent =>
:nullify
end
--

The last has_many is commented out so that I can at least get this
working, and then I''ll add that in later.  Also note that the
:dependent
has been commented out.  Is this deprecated or no longer supported?
What''s the deal?

committee.rb
--
class Committee < ActiveRecord::Base
  validates_presence_of :name
  has_and_belongs_to_many :senators #, :dependent => :nullify
  #has_one :head, :class_name => "Senator" #, :dependent =>
:nullify
end
--

Same as before on the comments.

Also, for my view I am trying the following:
--
<p><label
for="senator_committee">Committee</label><br/>
<%= select(:senator, :committees,
           Committee.find(:all).map {|c| [c.name, c.id]},
{:include_blank => true}, {:multiple => true}) %>
</p>
--

On the view I get the following error:

ActiveRecord::StatementInvalid

and the trace:

/usr/lib/ruby/gems/1.8/gems/activerecord-1.15.3/lib/active_record/connection_adapters/sqlite_adapter.rb:360:in
`table_structure''
/usr/lib/ruby/gems/1.8/gems/activesupport-1.4.2/lib/active_support/core_ext/object/misc.rb:23:in
`returning''
/usr/lib/ruby/gems/1.8/gems/activerecord-1.15.3/lib/active_record/connection_adapters/sqlite_adapter.rb:359:in
`table_structure''
/usr/lib/ruby/gems/1.8/gems/activerecord-1.15.3/lib/active_record/connection_adapters/sqlite_adapter.rb:210:in
`columns''
/usr/lib/ruby/gems/1.8/gems/activerecord-1.15.3/lib/active_record/associations/has_and_belongs_to_many_association.rb:165:in
`finding_with_ambigious_select?''
/usr/lib/ruby/gems/1.8/gems/activerecord-1.15.3/lib/active_record/associations/has_and_belongs_to_many_association.rb:55:in
`find''
/usr/lib/ruby/gems/1.8/gems/activerecord-1.15.3/lib/active_record/associations/association_collection.rb:159:in
`find_target''
/usr/lib/ruby/gems/1.8/gems/activerecord-1.15.3/lib/active_record/associations/association_proxy.rb:131:in
`load_target''
/usr/lib/ruby/gems/1.8/gems/activerecord-1.15.3/lib/active_record/associations/association_proxy.rb:29:in
`respond_to?''
/usr/lib/ruby/gems/1.8/gems/actionpack-1.13.3/lib/action_view/helpers/form_options_helper.rb:116:in
`options_for_select''
/usr/lib/ruby/gems/1.8/gems/activerecord-1.15.3/lib/active_record/base.rb:1358:in
`inject''
/usr/lib/ruby/gems/1.8/gems/actionpack-1.13.3/lib/action_view/helpers/form_options_helper.rb:114:in
`each''
/usr/lib/ruby/gems/1.8/gems/actionpack-1.13.3/lib/action_view/helpers/form_options_helper.rb:114:in
`inject''
/usr/lib/ruby/gems/1.8/gems/actionpack-1.13.3/lib/action_view/helpers/form_options_helper.rb:114:in
`options_for_select''
/usr/lib/ruby/gems/1.8/gems/actionpack-1.13.3/lib/action_view/helpers/form_options_helper.rb:302:in
`to_select_tag''
/usr/lib/ruby/gems/1.8/gems/actionpack-1.13.3/lib/action_view/helpers/form_options_helper.rb:66:in
`select''
#{RAILS_ROOT}/app/views/admin/_form.rhtml:26:in
`_run_rhtml_47app47views47admin47_form46rhtml''
#{RAILS_ROOT}/app/views/admin/edit.rhtml:4:in
`_run_rhtml_47app47views47admin47edit46rhtml''
#{RAILS_ROOT}/app/views/admin/edit.rhtml:3:in
`_run_rhtml_47app47views47admin47edit46rhtml''

Any help at all would be much appreciated.

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Andy Koch

2007-Jul-17 16:10 UTC

head link

Re: habtm confusion

Frew Schmidt schrieb:> Hello friends!
> 
> I am trying to make a database that will have a group of people set to
> committees, and a person can be in multiple committees, and a committee
> obviously has multiple people.  The people are senators at my
> university.  These are my current models:
> 
> senator.rb:
> --
> class Senator < ActiveRecord::Base
>   validates_presence_of :first_name, :last_name, :floor
>   has_and_belongs_to_many :committees#, :dependent => :nullify
>   #has_many :chairs, :class_name => "Committee"#, :dependent
=> :nullify
> end
> --
> 
> The last has_many is commented out so that I can at least get this
> working, and then I''ll add that in later.  Also note that the
:dependent
> has been commented out.  Is this deprecated or no longer supported?
> What''s the deal?
> 
> committee.rb
> --
> class Committee < ActiveRecord::Base
>   validates_presence_of :name
>   has_and_belongs_to_many :senators #, :dependent => :nullify
>   #has_one :head, :class_name => "Senator" #, :dependent =>
:nullify
> end
> --
> 
> Same as before on the comments.
> 
> Also, for my view I am trying the following:
> --
> <p><label
for="senator_committee">Committee</label><br/>
> <%= select(:senator, :committees,
>            Committee.find(:all).map {|c| [c.name, c.id]},
> {:include_blank => true}, {:multiple => true}) %>
> </p>
> --
> 
> On the view I get the following error:
> 
> ActiveRecord::StatementInvalid
> 
> and the trace:
> 
>
/usr/lib/ruby/gems/1.8/gems/activerecord-1.15.3/lib/active_record/connection_adapters/sqlite_adapter.rb:360:in
> `table_structure''
>
/usr/lib/ruby/gems/1.8/gems/activesupport-1.4.2/lib/active_support/core_ext/object/misc.rb:23:in
> `returning''
>
/usr/lib/ruby/gems/1.8/gems/activerecord-1.15.3/lib/active_record/connection_adapters/sqlite_adapter.rb:359:in
> `table_structure''
>
/usr/lib/ruby/gems/1.8/gems/activerecord-1.15.3/lib/active_record/connection_adapters/sqlite_adapter.rb:210:in
> `columns''
>
/usr/lib/ruby/gems/1.8/gems/activerecord-1.15.3/lib/active_record/associations/has_and_belongs_to_many_association.rb:165:in
> `finding_with_ambigious_select?''
>
/usr/lib/ruby/gems/1.8/gems/activerecord-1.15.3/lib/active_record/associations/has_and_belongs_to_many_association.rb:55:in
> `find''
>
/usr/lib/ruby/gems/1.8/gems/activerecord-1.15.3/lib/active_record/associations/association_collection.rb:159:in
> `find_target''
>
/usr/lib/ruby/gems/1.8/gems/activerecord-1.15.3/lib/active_record/associations/association_proxy.rb:131:in
> `load_target''
>
/usr/lib/ruby/gems/1.8/gems/activerecord-1.15.3/lib/active_record/associations/association_proxy.rb:29:in
> `respond_to?''
>
/usr/lib/ruby/gems/1.8/gems/actionpack-1.13.3/lib/action_view/helpers/form_options_helper.rb:116:in
> `options_for_select''
>
/usr/lib/ruby/gems/1.8/gems/activerecord-1.15.3/lib/active_record/base.rb:1358:in
> `inject''
>
/usr/lib/ruby/gems/1.8/gems/actionpack-1.13.3/lib/action_view/helpers/form_options_helper.rb:114:in
> `each''
>
/usr/lib/ruby/gems/1.8/gems/actionpack-1.13.3/lib/action_view/helpers/form_options_helper.rb:114:in
> `inject''
>
/usr/lib/ruby/gems/1.8/gems/actionpack-1.13.3/lib/action_view/helpers/form_options_helper.rb:114:in
> `options_for_select''
>
/usr/lib/ruby/gems/1.8/gems/actionpack-1.13.3/lib/action_view/helpers/form_options_helper.rb:302:in
> `to_select_tag''
>
/usr/lib/ruby/gems/1.8/gems/actionpack-1.13.3/lib/action_view/helpers/form_options_helper.rb:66:in
> `select''
> #{RAILS_ROOT}/app/views/admin/_form.rhtml:26:in
> `_run_rhtml_47app47views47admin47_form46rhtml''
> #{RAILS_ROOT}/app/views/admin/edit.rhtml:4:in
> `_run_rhtml_47app47views47admin47edit46rhtml''
> #{RAILS_ROOT}/app/views/admin/edit.rhtml:3:in
> `_run_rhtml_47app47views47admin47edit46rhtml''
> 
> Any help at all would be much appreciated.
> 
first, you have a "committees_senators" table to manage your many-many
join

second, your rhtml looks odd to me, I haven''t used that in a while but
I
think the bit...

:senator, :committees,

... looks wrong

I''m guessing you want a list of committees.  You should have something 
more like...

<p><label
for="senator_committee">Committee</label><br/>
 > <%= select(''committee'',
''committee_id'',
 >            Committee.find(:all).map {|c| [c.name, c.id]},
 > {:include_blank => true}, {:multiple => true}) %>
 > </p>

... if you want the committees a senator is associated with you''ll need
to add some extra code, something like ":selected => [Arr of Committee 
Id''s]" should work

finally, I think :dependent is for has_many, not habtm.  You should 
check the documentation to be certain.  http://api.rubyonrails.org

good luck,

andy koch


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Frew Schmidt

2007-Jul-17 16:39 UTC

head link

Re: habtm confusion

Thanks for the reply Andy!
> first, you have a "committees_senators" table to manage your
many-many
> join
I know that, but that''s abstracted away right?  I don''t need
to deal
with it, do I?
> <p><label
for="senator_committee">Committee</label><br/>
>  > <%= select(''committee'',
''committee_id'',
>  >            Committee.find(:all).map {|c| [c.name, c.id]},
>  > {:include_blank => true}, {:multiple => true}) %>
>  > </p>
as for the rhtml, the docs said the following:

  select(object, method, choices, options = {}, html_options = {})

so I presumed that I wanted :senator, :committees, but now that I think 
about that, that really doesn''t make a whole lot of sense.
> 
> ... if you want the committees a senator is associated with you''ll
need
> to add some extra code, something like ":selected => [Arr of
Committee
> Id''s]" should work
Nah, I''ll do that later, once I have the basics figured out.
> finally, I think :dependent is for has_many, not habtm.  You should
> check the documentation to be certain.  http://api.rubyonrails.org
Yeah, I realized last night that :dependent really doesn''t make any 
sense at all for habtm, because there is the intermediary table.  I''m 
sure I don''t need to explain it to you guys.

Thanks a bunch for the tips.  When I get time I will make modifications 
based on this and see how things go.

-fREW

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Andy Koch

2007-Jul-17 16:55 UTC

head link

Re: habtm confusion

Frew Schmidt schrieb:> Thanks for the reply Andy!
> 
>> first, you have a "committees_senators" table to manage your
many-many
>> join
> 
> I know that, but that''s abstracted away right?  I don''t
need to deal
> with it, do I?
> 
> 
> -fREW
> 
correct, but you must first create the table in your DB with appropriate 
structure


/ak


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Frew Schmidt

2007-Jul-17 17:05 UTC

head link

Re: habtm confusion

Andy Koch wrote:> Frew Schmidt schrieb:
>> Thanks for the reply Andy!
>> 
>>> first, you have a "committees_senators" table to manage
your many-many
>>> join
>> 
>> I know that, but that''s abstracted away right?  I
don''t need to deal
>> with it, do I?
>> 
> 
>> 
>> -fREW
>> 
> 
> correct, but you must first create the table in your DB with appropriate
> structure
> 
Oooh!

I never made that connection.  Here is the migration that I have made to 
define the table.  Tell me if anything looks totally wrong with it:

005_create_committees_senators.rb
--
class CreateCommitteesSenators < ActiveRecord::Migration
  def self.up
    create_table :committees_senators do |t|
      t.column :committee_id, :integer
      t.column :senator_id, :integer
    end
  end

  def self.down
    drop_table :committees
  end
end
--

(It seems to have worked so far.)

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Andy Koch

2007-Jul-18 15:45 UTC

head link

Re: habtm confusion

Frew Schmidt schrieb:> Andy Koch wrote:
>> Frew Schmidt schrieb:
>>> Thanks for the reply Andy!
>>>
>>>> first, you have a "committees_senators" table to
manage your many-many
>>>> join
>>> I know that, but that''s abstracted away right?  I
don''t need to deal
>>> with it, do I?
>>>
>>> -fREW
>>>
>> correct, but you must first create the table in your DB with
appropriate
>> structure
>>
> 
> Oooh!
> 
> I never made that connection.  Here is the migration that I have made to 
> define the table.  Tell me if anything looks totally wrong with it:
> 
> 005_create_committees_senators.rb
> --
> class CreateCommitteesSenators < ActiveRecord::Migration
>   def self.up
>     create_table :committees_senators do |t|
>       t.column :committee_id, :integer
>       t.column :senator_id, :integer
>     end
>   end
> 
>   def self.down
>     drop_table :committees
>   end
> end
> --
> 
> (It seems to have worked so far.)
> 

close, but you''re missing a few bits.  See this rewrite...

def self.up
create_table :committees_senators, :id => false do |t|
       t.column :committee_id, :integer, :null => false
       t.column :senator_id, :integer, :null => false
end

say "Add unique index on ''committees_senators''",
true
add_index(:committees_senators, [:committee_id, :senator_id], :unique => 
true)
end

...
The difference is:
1. this removes the ''id'' column from your join table with the
":id =>
false", it is not needed since the joined pairs are the key
2. enforces in DB that neither ID in a pair may ever be null (:null => 
false)
3. creates a unique index on the table, while this isn''t a true primary
key index it does ensure you won''t have any duplicity in the table.

And that should do it.

andy


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