empty class field in RoR

Question

On the Rails Guide, I saw a class was defined as

class Person < ActiveRecord::Base
end

and then it wrote

>>p = Person.new(:name => "John Doe")
=>#<Person id: nil, name: "John Doe", created_at: nil, :updated_at: nil

Since class Person has no field, why here it is valid to pass a :name attribute to the constructor? Shouldn't there be some error with it?

Also, why id, name, created_at all have no colon but :updated_at has one?

Answer 1

Because your class inherits from ActiveRecord::Base and ActiveRecords looks at your database and dynamically creates attributes that match the columns in the corresponding database table.

updated_at doesn't have a column either. Please look again carefully. It must be a mistake.

Answer 2

To see the fields defined in an ActiveRecord class you need to look at the db/schema.rb file. That will show you the fields that have been created through migrations.