属于同一模型的2个模型之间的ActiveRecord关联

Question

Rails newbie, so bear with me here. I need advice on how to properly set up the active record associations between 2 of my models.

As it stands right now, I have a User model. A User has_many Contacts. And a User has_many Posts. Simply put:

class User < ApplicationRecord
  has_many :posts, dependent: :destroy
  has_many :contacts, dependent: :destroy

class Contact < ApplicationRecord
  belongs_to :user

class Post < ApplicationRecord
  belongs_to :user

A user can send a post to one or more of their contacts (while that action is just something that triggers an email, I need to be able to track and display which contacts they've sent each post to). They can send a Post to many Contacts, and they may (over time) send each Contact more than 1 Post.

I'm a little uncertain how to associate Post and Contacts. Is it just a simple Post has_many Contacts (or vice versa)? Or should it be that a Post has_many Contacts THROUGH a User?

While I'm normally one who learns by trial and error, this is one of those situations where I'm worried if I go to far down the wrong path here, I'll figure it out so late that it'll be painful to undo - so thanks for any advice.

I'm using Rails 5 for what it's worth.

Answer 1

What you are looking for is a many-to-many relationship. Since a post can be associated with many contacts, and a contact can be associated with many posts.

Here is a great read for the many-to-many relationship

Basically, you will be created a association table to help link the post and contacts table.

class Contact < ApplicationRecord
  belongs_to :user
  has_many :posts, through: post_contact

class Post < ApplicationRecord
  belongs_to :user
  has_many :contacts, throught: post_contact

You will be created a new join table called post_contact (or whatever you want) and that table provides the association between posts and contacts.

Hope this helps.

Answer 2

you don't necessarily need a join between Post and Contacts , ie you could write @post.user.contacts or @contact.user.posts ,though it depends on your use-case.

But say you did want to create an association for Post to get all the comments of the same user. You could write:

class Post < ActiveRecord::Base
  has_many :contacts_of_user, through: :user, source: :contacts
end

You can use this same logic to implement contact.posts as well.