Declaring relationships in sequelize? - mysql

Question

I've got three models I am trying to define a relationship between them.
Models:
User
Payment
Debtor
User has many Payments
Payment belongs to User
Payment has many Debtors
Debtor belongs to Payment
Debtor belongs to Payment
Do I need to define the relationship in the source and the target? i.e.
User.hasMany(Payment, {as: 'Payments'})
and also
Payment.belongsTo(User)
or can I get away with just defining it in one model?
I appear to get errors when trying to define it in both. The model I import is undefined and therefore when I try pass it into the "belongsTo()" or "hasMany()" functions I get the error called with something that's not an instance of Sequelize.Model
When I only include it in one model, it doesn't create the relationship correctly.
My models are as follows:
Payment model:
import { sequelize } from '../config';
import Sequelize from 'sequelize';
import User from './User';
const Payment = sequelize.define('payment', {
amount: {
type: Sequelize.FLOAT
},
reference: {
type: Sequelize.STRING
},
user_id: {
type: Sequelize.INTEGER
}
});
Payment.belongsTo(User)
export default Payment;
User model:
import { sequelize } from '../config';
import Sequelize from 'sequelize';
import Payment from './Payment';
const User = sequelize.define('user', {
email: {
type: Sequelize.STRING
},
username: {
type: Sequelize.STRING
},
firstName: {
type: Sequelize.STRING
},
lastName: {
type: Sequelize.STRING
},
facebookID: {
type: Sequelize.STRING
}
});
User.hasMany(Payment, {as: 'Payments'})
export default User;
// EDIT
When I try create a new user with a payment, I get the error payment is not associated to user!
exports.create = (req, res) => {
User.create({
email: 'test3#gmail.com',
firstName: "Test",
lastName: "Test",
username: 'fnord',
payment: [
{ amount: 10.00},
]
}, {
include: [ Payment ]
})
}

Answer 1

That happens because in payment you require User model and vice-versa, in user you require Payment (circular dependency). In order to avoid this situation you would have to declare both models in the same file or you could follow the Sequelize recommended way
module.exports = (sequelize, DataTypes) => {
return sequelize.define('modelName', {
// attributes
}, {
// additional options, like classMethods in which you could create the association
classMethods: {
associate: function(models) {
this.belongsTo(models.Model);
this.hasMany(models.Model);
}
}
});
}
In order to achieve it you would have to use the sequelize-cli module. If you install it, you could use sequelize init command which would generate a file which registers all models to the sequelize (all those models are initially in one location, however you can change it by modifying the auto generated file).
In this case, sequelize iterates over every model, registers it (with use of sequelize.import() method) and calls the associate function which creates relations between models. This way would prevent the situation you have mentioned.

Answer 2

if Someone is struggling with Sequelize associations like me, this might help for you as this is not mentioned any where in documentation that how you can make associations if you are using Sequelize.define i was also facing an issue and made this work for me
'use strict';
module.exports = (sequelize, DataTypes) => {
const User = sequelize.define('User', {
id: {
type: DataTypes.BIGINT,
primaryKey: true,
},
name: {
type: DataTypes.STRING
},
email: {
type: DataTypes.STRING,
unique : true,
},
password: {
type: DataTypes.STRING
},
status: {
type: DataTypes.STRING
},
});
let Bookmark = sequelize.model('Bookmark');
User.hasMany(Bookmark,{foreignKey : 'user_id', as 'bookmarks'});
return User;
};
hope it works!