In this section we will explain how to use aggregation operators. Aggregation operators are divided into two parts. Within each stage, we use expression operators to compare and process values. Between different stages, we use aggregation stage operators to define the data that will get passed on from one stage to the next as its as the format.
Aggregation operators
Aggregation stage operators
An aggregation pipeline is composed of different stages. These stages are declared in an array and executed sequentially, the output of every stage being the input of the next one.
The $out stage has to be the final stage in an aggregation pipeline, outputting data to an output collection by replacing or adding to the existing documents...
