What I'm doing wrong, has_and_belong_to_many

rubyonrails-talk
1

Hello, I'm trying to insert into my migrate but when I try on rails console this error shows:

1.9.3-p0 :001 > group = Group.new => #<Group id: nil, name: nil, description: nil, created_at: nil, updated_at: nil> 1.9.3-p0 :002 > group.name = "Group Name" => "Group Name" 1.9.3-p0 :003 > group.description = "Description" => "Description" 1.9.3-p0 :004 > group.save    (0.2ms) BEGIN   SQL (0.4ms) INSERT INTO `groups` (`created_at`, `description`, `name`, `updated_at`) VALUES ('2012-02-14 01:39:22', 'Description', 'Group Name', '2012-02-14 01:39:22')    (124.5ms) COMMIT => true 1.9.3-p0 :005 > email = Email.new => #<Email id: nil, name: nil, email: nil, sex: "M", created_at: nil, updated_at: nil> 1.9.3-p0 :006 > email.name = "Gremio10" => "Gremio10" 1.9.3-p0 :007 > email.email = "gremio@10.com" => "gremio@10.com" 1.9.3-p0 :008 > email.save    (0.2ms) BEGIN   SQL (0.5ms) INSERT INTO `emails` (`created_at`, `email`, `name`, `sex`, `updated_at`) VALUES ('2012-02-14 01:39:56', 'gremio@10.com', 'Gremio10', 'M', '2012-02-14 01:39:56')    (65.6ms) COMMIT => true 1.9.3-p0 :009 > group << email NoMethodError: undefined method `<<' for #<Group:0xa7efb80>   from /home/felipe/.rvm/gems/ruby-1.9.3-p0/gems/activemodel-3.2.1/lib/active_model/attribute_methods.rb:407:in `method_missing'   from /home/felipe/.rvm/gems/ruby-1.9.3-p0/gems/activerecord-3.2.1/lib/active_record/attribute_methods.rb:126:in `method_missing'   from (irb):9   from /home/felipe/.rvm/gems/ruby-1.9.3-p0/gems/railties-3.2.1/lib/rails/commands/console.rb:47:in `start'   from /home/felipe/.rvm/gems/ruby-1.9.3-p0/gems/railties-3.2.1/lib/rails/commands/console.rb:8:in `start'   from /home/felipe/.rvm/gems/ruby-1.9.3-p0/gems/railties-3.2.1/lib/rails/commands.rb:41:in `<top (required)>'   from script/rails:6:in `require'   from script/rails:6:in `<main>' 1.9.3-p0 :010 >

My EmailModel

class Email < ActiveRecord::Base   has_and_belongs_to_many :groups   validate :email end

My GroupModel

class Group < ActiveRecord::Base   has_and_belongs_to_many :emails   validate :name end

My GroupsMigrate

class CreateGroups < ActiveRecord::Migration   def change     create_table :groups do |t|       t.string "name"       t.string "description"       t.timestamps     end   end

  def down     drop_table :groups   end end

My EmailsMigrate

class CreateEmails < ActiveRecord::Migration   def change     create_table :emails do |t|       t.string "name"       t.string "email"       t.string "sex", :default => "M", :limit => 1       t.timestamps     end   end

  def down     drop_table :emails   end end

My EmailsGroupsMigrate

class CreateEmailsGroupsJoin < ActiveRecord::Migration   def up     create_table :emails_groups, :id => false do |t|       t.references :email       t.references :group     end

    add_index :emails_groups, [ "email_id", "group_id" ]   end

  def down     drop_table :emails_groups   end end

Thank you.

2

Hello, I'm trying to insert into my migrate but when I try on rails console this error shows:

...

1.9.3-p0 :009 > group << email NoMethodError: undefined method `<<' for #<Group:0xa7efb80>

This is the chunk you need to worry about. It's telling you that you haven't defined any << method for your Group model. AR doesn't provide one, as such a thing just wouldn't make sense for most models.

class Email < ActiveRecord::Base has_and_belongs_to_many :groups validate :email end

...

class Group < ActiveRecord::Base has_and_belongs_to_many :emails validate :name end

You may also want to consider using "has_many :through" rather than has_and_belongs_to_many. I've heard horror stories of people having trouble getting HABTM to work right (though I never had problems with it myself), and if you ever decide you want to "decorate" that relationship with any additional data, it can be very difficult to retrofit a HABTM relationship to become HMT.

-Dave

3

If I don't have the method '<<', how can I install on my rails ?

4

If you have a has_many relationship or if you have any collection, you will be able to use the append method << .

att

5

My error:

I was doing this -> group << email

But the correct is doing this -> group.emails << email

Thank you