Comparison of two arrays

Frequently, when analyzing data and computing summary values for different time periods, you also want to compare what has changed in the data between those periods. Such last-mile comparisons can be left to the client application to perform using the programming language available there. However, as you will discover in this example, an aggregation can invariably perform this action for you.

Note

For this example, you require MongoDB version 4.4 or above. This is because you'll be using the $first array operator introduced in MongoDB version 4.4.

Scenario

You are an IT administrator managing virtual machine deployments in a data center to host a critical business application in a few environments (e.g., production and QA). A database collection captured the configuration state of each virtual machine across two days. You want to generate a report showing what configuration changes people made to the virtual machines (if any) between these...