I want to extend Conversation model, so that i can use an association with it. I have done it by creating a file named 'conversation.rb' in app/models directory in this way:

```
Mailboxer::Conversation.class_eval do
  belongs_to :device, class_name: "Device", foreign_key: 'device_id'
end

```

I have also added a column named 'device\_id' in conversations table.

But when i tries:

```
Conversation.last.device

```

It say:

```
NoMethodError: undefined method `device' for #<Mailboxer::Conversation:0x007fe83e6ae7c0>

```