Referencing Documents between 2 MongoDB Collections - node.js

Question

I'm building an app where employees can be added to the database and each employee belongs to a particular company, which can be chosen from a select field on the form. The form to add employees also contains a salary field and I would like to be able to display the companies with their total salary expense (based on the sum of salaries of its employees).
At first, I imagined I would use a single "employees" collection. Then, for example, choose "Apple" as the company, and finally, in the end, I would end up with a list of employee objects where I can loop through all the employees where "Apple" was the company and sum all the salary fields. This ended up being a poor approach. Next, I decided to create a separate collection of "companies". Then, before saving an employee, I look up the company object ID, and save that as the company.
For instance,
{ firstName: "Bob", lastName, "Smith", company: "5b62a456e7179a07334478a5", salary: 7}
Where "5b62a456e7179a07334478a5" is the "_id" field of Apple.
How do I continue to define this relationship in MongoDB?
Do I add an employees field to each company and try to save each employee to a company upon saving them to the employee's collection? In this way, I can try to access the sum of all employees within each company to obtain a total salary expense.
But I would then have to write to two different collections each time a new employee is saved. Also, what would the flow of that even look like? I would need to use the company _id field to look up the company and then save the employee to the company. So, would I have to perform a query and two writes on each new employee save?

Answer 1

You can use the lookup feature to do a "join"
db.table1.aggregate([{
$lookup: {
from: "table2",
localField: "table2column",
foreignField: "table1key",
as: "alias"
},
{
$project:{
//columns you want
}
}
}])
That being said...if your data is relational and not obscenely huge, a relational database might be a better choice.