Embrace composability for increased productivity

An aggregation pipeline is an ordered series of instructions, called stages. The entire output of one stage forms the whole input of the next stage, and so on—without any side effects. Pipelines exhibit high composability, where stages are stateless, self-contained components selected and assembled in various combinations (pipelines) to satisfy specific requirements. This property of aggregation pipelines makes iterative prototyping possible, with straightforward testing after each increment.

With MongoDB aggregations, you can take a complex problem, requiring a complex aggregation pipeline, and break it down into straightforward individual stages, where each step can be developed and tested in isolation. To better comprehend composability, it may be helpful to memorize the following visual model, in Figure 2.1:

Figure 2.1: Aggregation pipeline model

Suppose you have two pipelines with each pipeline...