Sequelize关联不起作用

Question

我有这两个模型

module.exports = function (sequelize, DataTypes) {
    return sequelize.define('transportationType', {
        description: {
            type: DataTypes.STRING,
            allowNull : false
        }
    })
}

---

module.exports = function (sequelize, DataTypes) {
    return sequelize.define('Transportation', {
        code: DataTypes.INTEGER,
        description: DataTypes.STRING,
        seatQty: DataTypes.INTEGER
    })
}

这是关联

db.Transportation.belongsTo(db.TransportationType);

我制作了这样的api

var code = parseInt(req.body.code);
var desc = req.body.desc;
var seat = parseInt(req.body.seat);
var type = parseInt(req.body.TransportationType);
db.TransportationType.findById(type)
    .then(snap => {
        db.Transportation.setTransportationType(snap); 
        db.Transportation.create({
            code: code,
            description: desc,
            seatQty: seat
        })
        .then(data => console.log(data))
        .catch(err => res.json(err));
    })

当我使用postman运行代码时，控制台说

  

db.Transportation.setTransportationType is not a function.

我确定文档会说它会运行，但不是