For our second example, we are going to use a more complex use case on a transaction with three different collections.
We are going to simulate a shopping cart and payment transaction process for an e-commerce application using MongoDB. Using the sample code that we'll provide at the end of this section, we will initially populate the database with the following data.
Our first collection is the users collection with one document per user:
> db.users.find(){ "_id" : ObjectId("5bc22f35f8d89f2b9e01d0fd"), "user_id" : 1, "name" : "alex" }{ "_id" : ObjectId("5bc22f35f8d89f2b9e01d0fe"), "user_id" : 2, "name" : "barbara" }
Then we have the carts collection with one document per cart, which is linked via the user_id to our ...
