orphan habtm rows

rubyonrails-talk
1

HI,

i use models User and Groups connected with many to many association, so i have users table, groups and groups_users.

lets say i create one user and one group. next i add a group to user. so now my table groups_users has one entry i.e.

group_id | user_id _________|________      1 | 1

ok, when i delete both my group and user, above entry is not deleted, thus leaving alone without any reason.. its just an orphan record, which is useless.

is there any parameter in rails that removes such records ? i dont want to have too many useless records at all.

btw. its not :dependant => :destroy parameter, this applies only to has_many association...

regards.

2

Carsten Gehling pisze:

Piotr Nowak wrote:

group_id | user_id _________|________      1 | 1

...

btw. its not :dependant => :destroy parameter, this applies only to has_many association...

I know, that it is not directly an answer to your current problem. But perhaps you should change your HABTM to a "has_many :through" relationship

Like this:

1) Change above table from "users_groups" to "memberships" and add an auto-incremented id field (of course as primary key)

2) Create a new model Membership with these declarations:

belongs_to :user belongs_to :group

3) in your Group model, replace the HABTM declaration with this:

has_many :memberships, :dependent => :destroy has_many :users, :through => :membership

4) ditto in the User model:

has_many :memberships, :dependent => :destroy has_many :groups, :through => :membership

You ought to be able to do this on your existing database and application without changing any other program lines. The access to the associated data are the same. And the :dependant declaration will take care of future orphans.

Hope this helps.

- Carsten

quite interesting, ill see if that works for me. btw. i wonder why something simple isnt done with regular habtm relationship..

anyway, thanks a lot Carsten :slight_smile: have a nice day (evening)

3

Carsten Gehling pisze:

Piotr Nowak wrote:

btw. i wonder why something simple isnt done with regular habtm relationship..

I can't remember when the :dependent keyword was added to ActiveRecord, but I know, that ever since Rails 1.2, "has_many :trough" has been favored by the Rails core team over HABTM.

BTW: "has_many :through" has another advantage over HABTM: In your "memberships" table, you are allowed to add attributes e.g. like this

memberships --------------- id (int) user_id (int) group_id (int) valid_from (datetime) valid_to (datetime)

and access these from your model code.

anyway, thanks a lot Carsten :slight_smile: have a nice day (evening)

You are very welcome, I am (unfortunately) not often on the Ruby-forum, but it gives me pleasure when I'm able to help others in need. :slight_smile:

You have a nice evening too.

- Carsten

ok ive done this, but when i do usr = User.find(:first) usr.groups

i get error:

ActiveRecord::HasManyThroughAssociationNotFoundError: Could not find the associa tion :membership in model User

my models and tables are as follows

class User < ActiveRecord::Base    has_many :memberships, :dependent => :destroy    has_many :groups, :through => :membership end

class Membership < ActiveRecord::Base    belongs_to :user    belongs_to :group end

class Group < ActiveRecord::Base    has_many :memberships, :dependent => :destroy    has_many :users, :through => :membership end

excerpt form my schema.rb:

   create_table "memberships", :force => true do |t|      t.column "group_id", :integer      t.column "user_id", :integer    end

any ideas ?

4

ok, figured it out :slight_smile:

class User < ActiveRecord::Base     has_many :memberships, :dependent => :destroy     has_many :groups, :through => :membership end

class Group < ActiveRecord::Base     has_many :memberships, :dependent => :destroy     has_many :users, :through => :membership end

should be:

class User < ActiveRecord::Base     has_many :memberships, :dependent => :destroy     has_many :groups, :through => :memberships end

class Group < ActiveRecord::Base     has_many :memberships, :dependent => :destroy     has_many :users, :through => :memberships end

In overall the through attribute value should be pluralized :slight_smile:

big thank you

5

Piotr Nowak pisze:

ok, figured it out :slight_smile:

class User < ActiveRecord::Base     has_many :memberships, :dependent => :destroy     has_many :groups, :through => :membership end

class Group < ActiveRecord::Base     has_many :memberships, :dependent => :destroy     has_many :users, :through => :membership end

should be:

class User < ActiveRecord::Base     has_many :memberships, :dependent => :destroy     has_many :groups, :through => :memberships end

class Group < ActiveRecord::Base     has_many :memberships, :dependent => :destroy     has_many :users, :through => :memberships end

In overall the through attribute value should be pluralized :slight_smile:

big thank you

>

well, although it works, it doesnt resolve my problem when i delete user or group, the membership item (containng both those user and group) is not deleted...

wonder why..

6

Piotr Nowak pisze:

Piotr Nowak pisze:

ok, figured it out :slight_smile:

class User < ActiveRecord::Base     has_many :memberships, :dependent => :destroy     has_many :groups, :through => :membership end

class Group < ActiveRecord::Base     has_many :memberships, :dependent => :destroy     has_many :users, :through => :membership end

should be:

class User < ActiveRecord::Base     has_many :memberships, :dependent => :destroy     has_many :groups, :through => :memberships end

class Group < ActiveRecord::Base     has_many :memberships, :dependent => :destroy     has_many :users, :through => :memberships end

In overall the through attribute value should be pluralized :slight_smile:

big thank you

well, although it works, it doesnt resolve my problem when i delete user or group, the membership item (containng both those user and group) is not deleted...

wonder why..

>

just noticed that it works only when i do destroy method on my user or group instead of delete...

7

Always use destroy() if possible.

- Carsten

i will, rails rocks !

i ve just switched from java/.net to rails and im so excited so far :slight_smile:

greets.

8

Carsten Gehling pisze:

Piotr Nowak wrote:

i will, rails rocks !

i ve just switched from java/.net to rails and im so excited so far :slight_smile:

Have you seen these?

http://www.railsenvy.com/tags/Commercials

Start with the ones in the bottom - they are fun and - IMHO quite accurate :slight_smile:

Been at a few of the langauges/frameworks myself earlier. Now I only do PHP and Rails - and PHP only because I have so many existing customers/solutions that I would hate to rewrite.

But you've made a good choice - you won't regret it!

- Carsten

yes, ive seen them all, pretty funny, especially rails vs .net #2 :slight_smile: starting 2 projects now in rails, im quite excited :slight_smile:

greets.