Reference
Operators 可以理解为 MongoDB 提供的开箱即用的一些基本的”算子参数”，供 MongoDB 的方法识别，去执行相应的任务，可以分为下面几类:
- Query and Projection Operators:Query operators provide ways to locate data within the database and projection operators modify how data is presented.
- Update Operators:Update operators are operators that enable you to modify the data in your database or add additional data.
- Aggregation Pipeline Stages:Available aggregation stages for Aggregation Pipeline.
- Aggregation Pipeline Operators:Aggregation pipeline operations have a collection of operators available to define and manipulate documents in pipeline stages.
- Query Modifiers:Query modifiers determine the way that queries will be executed.
