how to create parent/child associations in sequelize? - node.js

Question

I have a Employee and their dependents model defined in sequlieze. I have an employeeId foreign key column defined in the dependent table ( see my model class below) . but when i try to execute following command
models.Employee.findOne({where: { id: Number(id) }, include: [{ model: models.Dependent }]});
i get an error -> EagerLoadingError [SequelizeEagerLoadingError]: Dependent is not associated to Employee!
isn't specifying a foreign key in the dependent model , enough?
Employee model
module.exports = function(sequelize, DataTypes) {
const Employee = sequelize.define('Employee ', {
id : {
type: DataTypes.INTEGER(11),
allowNull: false,
autoIncrement:true,
primaryKey:true
},
Name : { ... }
Dependent model
module.exports = function(sequelize, DataTypes) {
const Dependent = sequelize.define('Dependent', {
id : {
type: DataTypes.INTEGER(11),
allowNull: false,
autoIncrement:true,
primaryKey:true
},
EmployeeId : {
type: DataTypes.INTEGER(11),
allowNull: true,
references : {
model : 'Employee ',
key:'id'
}
},
Name : { ... }

Answer 1

isn't specifying a foreign key in the dependent model, enough?
No, it's NOT enough if you want to use Eager Loading of sequelize.
You need to create sequelize associations for these models(Employee and Dependent for your case) in pairs, see Why associations are defined in pairs?
The references option in the model only creates an FK relationship between Dependent and Employee tables in the database(relationship for db level). Does not include associations of sequelize model(relationship for application level). When to use? see Enforcing a foreign key reference without constraints
Employee has many dependents and dependent belongs to one Employee. So you need to create One-To-Many relationships.
Employee.hasMany(Dependent);
Dependent.belongsTo(Employee);
create associations like above will create FK reference for tables implicitly.
Execution results:
Executing (default): CREATE TABLE IF NOT EXISTS "employees" ("id" SERIAL , "name" VARCHAR(255), PRIMARY KEY ("id"));
Executing (default): CREATE TABLE IF NOT EXISTS "dependents" ("id" SERIAL , "name" VARCHAR(255), "EmployeeId" INTEGER REFERENCES "employees" ("id") ON DELETE SET NULL ON UPDATE CASCADE, PRIMARY KEY ("id"));