# 1 classes

Let's add the classes Question and Answer to the model in stackoverflow.klass.

class Question
{
    id        : Long key id;
    title     : String minLength(15) maxLength(150);
    body      : String maxLength(30000);
}

id has the primitive type Long. The key modifier is similar to a database's primary key. The id modifier on the id property means that it's an auto-incrementing number, not a natural key.

title has the primitive type String with max length 150.

body has the primitive type String with max length 30000.

So far, this exactly matches the real Stack Overflow.

class Answer
{
    id        : Long key id;
    body      : String(30000);
    questionId: Long private;
}

Answer also has id and body but no title.

Answer has questionId with the private modifier. It's private to the data-layer; it will be used as a foreign key. Private properties cannot appear in projections, so questionId won't be part of service bodies; neither request bodies nor response bodies.