Question: I would like my `User` to be associated with specific `Email`'s, when they receive them.

In this way, I can look up an array of what emails they have received.

Originally, I was thinking of just creating a string field for the User table, and adding the unique ID to the array..

```
User.find(x).received_emails << Email.find(x).id

```

But there may be a better way to do this with associating models.

Recommendations?

Answer: 
You should check this link out:

[Rails association guide](http://guides.rubyonrails.org/association_basics.html)

It sounds like you're talking about a one to many sort of thing. If you use the association mechanism you'll get all the behavior you want, basically for free.
```
class Email < ActiveRecord::Base
  belongs_to :user
end

class User < ActiveRecord::Base
  has_many :received_emails, :class_name => 'Email'
end

User.find(x).received_emails << Email.find(y)

```

This approach would require adding a `user_id` column to the Email table.

You probably want to change this to a many-to-many association by adding a join table such as user\_emails with a UserEmail model. That table would have `user_id` and `email_id` columns.