Summary
In this chapter, you started your journey with basic aggregation expressions. You explored the different types of expressions and how to combine them using nesting to solve complex data transformations. Then you moved on to bootstrapping this knowledge to undertake typically complicated tasks related to mutating arrays and extracting detail from the contents of arrays. There was a particular focus on techniques for looping through array elements efficiently without necessarily having to resort to unwinding and regrouping documents, where you only need to process each document's array in isolation.
The next chapter will enable you to understand the impact of sharding on aggregation pipelines and how to ensure your pipelines run efficiently when your database is sharded.
