Question

Let’s say that I’m building an engine that has many blogs and many users. Users can have many blogs and blogs can have many users (users hasAndBelongsToMany blogs). I would create a pivot table called users_blogs which would look like this:

id user_id blog_id role

1  1       1       admin
2  1       2       poster
3  2       2       admin

So, user 1 belongs to blogs 1 and 2, and user 2 belongs to blog 2. User 1 is an admin in blog 1, and a poster in blog 2, and user 2 is an admin in blog 2.

There will also be posts. users_blogs will have many posts, and posts can have many users_blogs. They would be joined with a pivot table that would look like this:

id users_blog_id post_id
1  2             1
2  3             1

So, referring to users_blogs, user 1 on blog 2 collaborated with user 2 on blog 2 to create post 1.

I’m relatively new to MVC, so I’m wondering if A) the “role” data in the first table is where it’s supposed to be?, and B) Is there a more correct way to do this structure? Frameworks will do the magic for me, I just want to make sure that this makes sense, and I’ve got the correct naming conventions. I’m using Cakephp, but I also think that this question could be answered by a Rails programmer.

Thank you!

Answer 1

It looks like you’re on the right track. If I understand you, this is how it should be:

I didn’t completely understand one of your statements, so I’m going on the assumption that a post belongsTo a single blog like most.

First issue is, your “pivot table” naming convention must be in alphabetical order – so it should be blogs_users, not users_blogs. Seems minor, but won’t work otherwise.

Associations:

blog hasMany post
post belongsTo blog

user hasAndBelongsToMany blog //allowing more than one user to be associated to a blog
blog hasAndBelongsToMany user

user hasAndBelongsToMany post //allowing more than one user to be associated to a post
post hasAndBelongsToMany user

role hasAndBelongsToMany user //better to keep roles in a table that just a string
user hasAndBelongsToMany role //use 'with'=>'blogs_users' in your association
                              between user/roll

Tables:

users            (id, name, ...etc)
blogs            (id, title, ...etc)
roles            (id, role)
blogs_users      (id, user_id, role_id, blog_id)
posts            (id, title, blog_id)
posts_users      (id, post_id, user_id)

Update:

I’m not the best at this – still somewhat learning myself, but – off the top of my head, you could get the posts from blog 1 created by user 1 via something like this:

$blogId = '1';
$userId = '1';
$posts = $this->Post->find('all', array(
    'conditions' => array(
        'User.id' => $userId,
        'Blog.id' => $blogId
    )
);