sequelize Model.hasOne 错误:模型未关联到 ModelTwo

I keep getting the error "Error: Model is not associated to ModelTwo!"

app.get('/',function(req,res){
 db.Member.findAll({include:[{model:db.MemberProfile,as:'Profile'}]})
 .success(function(users){
  if(users){
   res.json(users);
  }else{
   res.send('no users');
  }
 });
});

//模型.js

module.exports = function(sequelize,sql) {
 return sequelize.define('Model', {
  //attributes
 });

 Model.hasOne('ModelTwo',{foreignKey:'model_id'});

};

//model_two.js

module.exports = function(sequelize,sql) {
 return sequelize.define('ModelTwo', {
  //attributes
 });

//no relationship defined. Tried ModelTwo.hasMany('Model',{foreignKey:'id'});
//but it yields the same resulting error
};