MongoDB Aggregation
Introduction
Aggregations operations process data records and return computed results. Aggregation operations group values from multiple documents together, and can perform a variety of operations on the grouped data to return a single result. MongoDB provides three ways to perform aggregation: the aggregation pipeline, the map-reduce function, and single purpose aggregation methods.
From Mongo manual https://docs.mongodb.com/manual/aggregation/
Syntax
- db.collection.aggregate(pipeline, options)
Parameters
| Parameter | Details |
|---|---|
| pipeline | array(A sequence of data aggregation operations or stages) |
| options | document(optional, available only if pipeline present as an array) |
Remarks
Aggregation framework in MongoDB is used to achieve common GROUP BY functionality of SQL.
Consider the following insertions in collection named transactions for every example.
> db.transactions.insert({ cr_dr : "D", amount : 100, fee : 2});
> db.transactions.insert({ cr_dr : "C", amount : 100, fee : 2});
> db.transactions.insert({ cr_dr : "C", amount : 10, fee : 2});
> db.transactions.insert({ cr_dr : "D", amount : 100, fee : 4});
> db.transactions.insert({ cr_dr : "D", amount : 10, fee : 2});
> db.transactions.insert({ cr_dr : "C", amount : 10, fee : 4});
> db.transactions.insert({ cr_dr : "D", amount : 100, fee : 2});
