如何在Ruby on Rails联接表中加载数据？

Question

I have the following join table that works:

class CreateRolesUsers < ActiveRecord::Migration
  def self.up
    create_table :roles_users,:id => false do |t|
      t.integer :role_id, :null => false
      t.integer :user_id, :null => false
    end    
  end

  def self.down
    drop_table :roles_users
  end
end

But I don't know how to load by default some data (syntax), I try that:

roleUser = RoleUser.create(:role_id => 2,:user_id => 1)
roleUser.save!

It does not work, is it RoleUser... or something else to use? RolesUser...etc.

Answer 1

That's provided that you have a model named RolesUser.

If you have a habtm association, the model is probably not there.

One way of loading roles could be;

user = User.create :name => 'John'
role = Role.create :name => 'admin'

user.roles << role

Answer 2

From what I understand, your user can have many roles , right? If so..

class User < ActiveRecord::Base
  has_and_belongs_to_many :roles
end

class Role < ActiveRecord::Base
  has_and_belongs_to_many :users
end

Then you can do

user = User.create :name => 'John'
role = Role.create :name => 'admin'
roles_users = RolesUser.create :user => user, :role => role

The has_and_belongs_to_many assoiation creates a join table with both FK. If you need extra data in the join table, you will need to use has_may :through instead of has_and_belongs_to_many .
I strongly recommend reading the guide on ActiveRecord associations . Good luck!

Answer 3

First when you have association has_and_belongs_to_many you actualy don't have model, you only have database table with plural name combined from models that are participating in association, for example

class User < ActiveRecord::Base
   has_and_belongs_to_many :roles
end

class Role < ActiveRecord::Base
   has_and_belongs_to_many :users
end

You don't get model named UserRoles, or UsersRoles, or UsersRole or any kind of model, this only makes some methods that you can use on User instance or Role instance to find for 1 user all of his roles, or to find all users with some role ant etc.

This works, that rails will look for database table with name roles_users (it looks for table that is combined with both model names in plural, ordering by alphabetical order, thats why its roles_users and not users_roles).

For particular user you can add roles or predefine existing ones, example:

# find one user
user = User.first
# get collection of roles
roles_c = Role.where("some conditional statement to find roles")
# set user roles to found collection
user.roles = roles_c
# save changes
user.save

This way you will get records in roles_users table with user_id of user and for every role in roles_c collection there will be record, for example:

# if user.id is 1
# and in roles_c you have 3 roles with id_s 2,5 and 34
# in roles_users table there will be created 3 records with

user_id => 1, role_id => 2
user_id => 1, role_id => 5
user_id => 1, role_id => 34

Other way is to add some roles,

user = User.first
roles_c = Role.where('conditional statement')
user.roles << roles_c
user.save

Answer 4

You're almost there. The table name is a plural form of the model name. The table is named RolesUsers , so the model is named RolesUser .

Also, I think you would prefer to use the new method if you're going to call save! after the fact. Calling create automatically saves the record.

rolesUser = RolesUser.new(role_id => 2,:user_id => 1)
rolesUser.save!

Recommended reading: http://api.rubyonrails.org/classes/ActiveRecord/Base.html