Aggregation Operations
Aggregation operations process multiple documents and return computed results. You can use aggregation operations to:
- Group values from multiple documents together.
- Perform operations on the grouped data to return a single result.
- Analyze data changes over time.
Aggregation Pipelines
An aggregation pipeline consists of one or more stages that process documents:
- Each stage performs an operation on the input documents. For example, a stage can filter documents, group documents, and calculate values.
- The documents that are output from a stage are passed to the next stage.
- An aggregation pipeline can return results for groups of documents. For example, return the total, average, maximum, and minimum values.
db.orders.insertMany( [
{ _id: 0, name: "Pepperoni", size: "small", price: 19,
quantity: 10, date: ISODate( "2021-03-13T08:14:30Z" ) },
{ _id: 1, name: "Pepperoni", size: "medium", price: 20,
quantity: 20, date : ISODate( "2021-03-13T09:13:24Z" ) },
{ _id: 2, name: "Pepperoni", size: "large", price: 21,
quantity: 30, date : ISODate( "2021-03-17T09:22:12Z" ) },
{ _id: 3, name: "Cheese", size: "small", price: 12,
quantity: 15, date : ISODate( "2021-03-13T11:21:39.736Z" ) },
{ _id: 4, name: "Cheese", size: "medium", price: 13,
quantity:50, date : ISODate( "2022-01-12T21:23:13.331Z" ) },
{ _id: 5, name: "Cheese", size: "large", price: 14,
quantity: 10, date : ISODate( "2022-01-12T05:08:13Z" ) },
{ _id: 6, name: "Vegan", size: "small", price: 17,
quantity: 10, date : ISODate( "2021-01-13T05:08:13Z" ) },
{ _id: 7, name: "Vegan", size: "medium", price: 18,
quantity: 10, date : ISODate( "2021-01-13T05:10:13Z" ) }
] )
Calculate Total Order Quantity
db.orders.aggregate( [
// Stage 1: Filter pizza order documents by pizza size
{
$match: { size: "medium" }
},
// Stage 2: Group remaining documents by pizza name and calculate total quantity
{
$group: { _id: "$name", totalQuantity: { $sum: "$quantity" } }
}
] )
Example output:
[
{ _id: 'Cheese', totalQuantity: 50 },
{ _id: 'Vegan', totalQuantity: 10 },
{ _id: 'Pepperoni', totalQuantity: 20 }
]
Calculate Total Order Value and Average Order Quantity
db.orders.aggregate( [
// Stage 1: Filter pizza order documents by date range
{
$match:
{
"date": { $gte: new ISODate( "2020-01-30" ), $lt: new ISODate( "2022-01-30" ) }
}
},
// Stage 2: Group remaining documents by date and calculate results
{
$group:
{
_id: { $dateToString: { format: "%Y-%m-%d", date: "$date" } },
totalOrderValue: { $sum: { $multiply: [ "$price", "$quantity" ] } },
averageOrderQuantity: { $avg: "$quantity" }
}
},
// Stage 3: Sort documents by totalOrderValue in descending order
{
$sort: { totalOrderValue: -1 }
}
] )
Example output:
[
{ _id: '2022-01-12', totalOrderValue: 790, averageOrderQuantity: 30 },
{ _id: '2021-03-13', totalOrderValue: 770, averageOrderQuantity: 15 },
{ _id: '2021-03-17', totalOrderValue: 630, averageOrderQuantity: 30 },
{ _id: '2021-01-13', totalOrderValue: 350, averageOrderQuantity: 10 }
]
References
https://www.mongodb.com/docs/manual/aggregation/
https://www.mongodb.com/docs/manual/core/aggregation-pipeline/