primaryKey
By default, the field 
id is used as primary key.Usage
simple
class User extends Model {  static entity = 'users'  static primaryKey = 'userId'  static fields () {    return {      userId: this.attr(null)    }  }}combined
class RoleUser extends Model {  static entity = 'roleUser'  static primaryKey = ['role_id', 'user_id']  static fields () {    return {      role_id: this.attr(null),      user_id: this.attr(null)    }  }}Typescript Declarations
const primaryKey: string | string[] = 'id'