How does one add an attribute to a model?

Yes, the solution by @JCorcuera is applicable, but I suggest applying a little more information to Rails to fulfill our requirement. Try this approach:

rails generate migration add_columnname_to_tablename columnname:datatype

For example:

rails generate migration add_password_to_users password:string

Active Record maps your tables columns to attributes in your model, so you don't need to tell rails that you need more, what you have to do is create more columns and rails is going to detect them, the attributes will be added automatically.

You can add more columns to your table through migrations:

rails generate migration AddNewColumnToMyTable column_name:column_type(string by default)

Example:

rails generate migration AddDataToPosts views:integer clicks:integer last_reviewed_at:datetime 

this will generate a file:

db/2017.....rb

Open it and add modify it if needed:

self.up  #add_column :tablename, :column_name, :column_type  add_column :posts, views, :integer  add_column :posts, clicks, :integer, default: 0end

Hope this helps.

If you are using the Rails 4.x you can now generate migrations with references, like this:

rails generate migration AddUserRefToProducts user:references

like you can see on rails guides