Question

I have a scenario where the models look like

create_table :users do |t|
  t.string :name
  t.timestamps
end

create_table :blogs do |t|
  t.string :url
  t.string :title
  t.text :description
  t.timestamps
end

create_table :posts do |t|
  t.integer :user_id, :null => false
  t.integer :blog_id, :null => false
  t.text :post_text
end

class Blog < ActiveRecord::Base
  has_many :users, :through =>:posts
  has_many :posts, :dependent=>true
end

class User < ActiveRecord::Base
  has_many :blogs
  has_many :posts, :through=>:blogs
end

class Post < ActiveRecord::Base
  belongs_to :blog
  belongs_to :user
end

The question I have is:
1. When a user is created, I would like to create a blog for him automatically.

@user = User.find_or_create_by_name(user_name)

How do I go about creating a blog?
@blog = Blog.find_or_create_by_user_id(@user)

I am getting the following error:

undefined method `find_or_create_by_user_id' for #<Class:0x1044735b0>

@blogs = @user.blogs

gives me:

 Mysql::Error: Unknown column 'blogs.user_id' in 'where clause': SELECT * FROM `blogs` WHERE (`blogs`.user_id=1234)

I know Blogs table does not have user_id column.
But isn’t the join supposed to take care of it?
What am I doing wrong here?

Thanks for your help

Answer 1

To use the Post model as the association table, the User model needs to be tweaked to properly demonstrate the association. Once done, you could use after_create to create a new blog for a newly created user.

class User < ActiveRecord::Base
  has_many :posts
  has_many :blogs, :through=>:posts
  after_create :add_blog

  private
  def add_blog
    blogs << Blog.new
  end

end

EDIT:

The best I know how to handle it is to explain what I “think” the relationships are attempting to accomplish then you tell me where I’m off and we go from there.

1) A User can “own” many blogs

2) A blog can have many posts

3) A post belongs to a single user and to a single blog

4) a blog can only have one “owner” (user)

5) Blogs can be “owned” by many users thereby giving them permission to post.

If 1-4 are true, and 5 false… that isn’t a “has_many :through” scenario or many-to-many relationship, just one-to-many relationships.

Accordingly, posts should not be used as an association table. There isn’t an association table needed.

add t.integer :user_id, :null => false to the blogs table

class Blog < ActiveRecord::Base
  belongs_to :users, 
  has_many :posts, :dependent=>:destroy # rec'd error in RoR3... replaced true with :destroy
end

class User < ActiveRecord::Base
  has_many :blogs, :dependent=>:destroy
  has_many :posts
  after_create :add_blog

  private
  def add_blog
    blogs << Blog.new
  end
end

class Post < ActiveRecord::Base
  belongs_to :blog
  belongs_to :user
end

If 5 is true, this would be a true many-to-many… but I don’t think that’s what you’re attempting to do.