Mongodb and node js transaction alternative and relations - node.js

Question

I am trying to implement relations on collections. My requirement is
Post request 1, json body:
{
"username":"aaa",
"password":"bbb",
"role":"owner",
"company":"SAS"
}
Post request 2, creating from first document so I got company name from previous json body:
{
"username":"eee",
"password":"fff",
"role":"engineer",
"company":"SAS"
}
Post request 3, creating from first document so I got company name from previous json body:
{
"username":"uuu",
"password":"kkk",
"role":"engineer",
"company":"SAS"
}
Post request 4, next company json body:
{
"username":"hhh",
"password":"ggg",
"role":"owner",
"company":"GVG"
}
Here company is foreign key field. How can I achieve company with id field without failing one another like transactions.
In mysql I will create two tables company, user and using transactions i will insert in both tables in single post using id's if any update in company name id will remain same for owner and engineer.
How can I achieve these in mongodb, with node.js?
In online searches I have found most suggest avoid transactions and using mongodb functionalities like mongodb embedded.

Answer 1

I would suggest you to start with making schemas for user and company using mongoose. Its an ODM(object document mapper) which is almost always used with node.js and mongodb
Now this is one to many relations. In relational databases as you have mentioned, you would make a company table and a user table.
In mongodb it "depends". If its one to "few" relationship you would just nest the users array into company's collection. Then since you are only updating a single document(pushing user to users array in company's document), you wont be needing any transactions. Single document update is always atomic(no matter how many fields you update on the same document).
But if each company can have large number of users(ever growing nested array is not good, as it can cause data fragmentation and bad performance), then its better to store the company's id in user's document. And even in this case you would not need transaction, since you are not updating the company's document.
Another reason for storing user as separate collection, is query issues. If you just want to query users its difficult if they are nested in companies. So basically you need to consider how you will query and figure out the number of relations then decide to nest of store is separate collections.

Answer 2

First of all, you should notice that Mongo is document-oriented DB, not a relation one. So if you need transactions and relation model, probably you should try to use any SQL relative database? Especially if you are more familiar with them?
About relation and data modeling: you should this article (or even entire part) at official Mongo docs, Data Modelling.
TL:DR, you could create two separate collections (the same as tables in SQL) like employees, and companies (by default, collection's name will be in plural forms). And store data separately.
So you employees will be stored like you mention above, but companies will be like:
{
_id: ObjectID("35473645632")
name: "SAS"
}, ...
and as for your employees collection, you should store not like, "company":"SAS", but, "company":"ObjectID("35473645632"), or even as array if you want it too. But don't forgot to edit you schema than.
You could use not just MongoDB's default _id but your own one, it could be any unique number/string combination
So, if your company will be renamed, your connection with other documents (employees) still will be there.
To request all/any of your employees with company name's you should use .aggregation framework with $lookup, instead of .find.