在rails中的has_many中的关联

Question

I am stuck at a small problem,but it has been so long for me trying to figure out what am i doing wrong. My scenario is i have a existing model user and now i create another model called `user_comment'. I have created below mentioned details:

User model:

class User < ActiveRecord::Base
has_many :user_comments
end

User_comment Model:

 class UserComment < ActiveRecord::Base
    belongs_to :user
    end

Migration File:

class CreateUserComments < ActiveRecord::Migration
  def change
    create_table :user_comments do |t|
      t.integer :user_id
      t.string  :comments
      t.timestamps
    end
  end
end

After running rake db:migrate i went to rails console and then to setup the relation between two tables i did the following and nothing is working

obj1= User.first

I added first new row in user_comments table and then did ..

obj2= UserComment.first

Doing obj1.obj2= obj2 is giving me

NoMethodError: undefined method `obj2=' for #<User:0x00000005f8e850>
    from /home/insane/.rvm/gems/ruby-2.1.0/gems/activemodel-3.2.11/lib/active_model/attribute_methods.rb:407:in `method_missing'
    from /home/insane/.rvm/gems/ruby-2.1.0/gems/activerecord-3.2.11/lib/active_record/attribute_methods.rb:149:in `method_missing'
    from (irb):3
    from /home/insane/.rvm/gems/ruby-2.1.0/gems/railties-3.2.11/lib/rails/commands/console.rb:47:in `start'
    from /home/insane/.rvm/gems/ruby-2.1.0/gems/railties-3.2.11/lib/rails/commands/console.rb:8:in `start'
    from /home/insane/.rvm/gems/ruby-2.1.0/gems/railties-3.2.11/lib/rails/commands.rb:41:in `<top (required)>'
    from script/rails:6:in `require'
    from script/rails:6:in `<main>'

Please help me how to form an association ..

Answer 1

obj1.obj2= obj2 is wrong, you need a space between obj1.obj2 and = .

But ob1.obj2 make no sense too(there is no obj2 method in User ).

Add an object to an association you could do:

user = User.first
comment = UserComment.first

# if both object are not nil, then you could do below
user.user_commentes << comment

Answer 2

Where does SmileComment suddenly come from?

Anyway, there are several things going wrong. First off, I would change the name of your model from UserComment to Comment. The fact that a comment belongs to an user is already made clear through your association. Calling User.first.user_comments seems a bit akward.

Let us start with a really basic example:

class User < ActiveRecord::Base
  has_many :comments
end

class Comment < ActiveRecord::Base
  belongs_to :user
end

As you did in your migration, the comments needs a user_id to reference the user it belongs to. After running the migration, calling the association is dead simple:

User.first.comments # Gives all comments belonging to that user

Or:

Comment.first.user # Gives the user that belongs to that comment

Answer 3

obj1.obj2= obj2 => self-referential loop?

---

You'll be best reading the Rails ActiveRecord associations guide - you'll find what you're dealing with is actually relatively simple to remedy

As described by @rails4guides.com , you'll be best renaming your UserComment model to just Comment (as this will allow you to associate any data you need with it -- if you wanted to extend later):

#app/models/user.rb
Class User < ActiveRecord::Base
    has_many :comments
end

#app/models/comment.rb
Class Comment < ActiveRecord::Base
    belongs_to :user
end

This is actually down to relational database naming conventions , whereby each table's data can be associated with another's. They do this with foreign_keys - which is how Rails uses the associations defined in your models to create the likes of @user.comments :

class Comments < ActiveRecord::Migration
  def change
    create_table :comments do |t|
      t.integer :user_id => this is the foreign_key, which means Rails can append these objects to your `user` object
      t.string  :comments
      t.timestamps
    end
  end
end

So if you want to give the user a set of comments, you'll just need to call the User object from your model, and since Rails' ActiveRecord associations automatically call any relational data through your schemas, you'll get comments appended to the @user object with @user.comments