Aggregation Pipelines
Aggregation operations allow you to group, sort, perform calculations, analyze data, and much more.
Aggregation pipelines can have one or more "stages". The order of these stages are important. Each stage acts upon the results of the previous stage.
Example
db.posts.aggregate([
// Stage 1: Only find documents that have more than 1 like
{
$match: { likes: { $gt: 1 } }
},
// Stage 2: Group documents by category and sum each categories likes
{
$group: { _id: "$category", totalLikes: { $sum: "$likes" } }
}
])
Sample Data
To demonstrate the use of stages in a aggregation pipeline, we will load sample data into our database.
From the MongoDB Atlas dashboard, go to Databases. Click the ellipsis and select "Load Sample Dataset". This will load several sample datasets into your database.
In the next sections we will explore several aggregation pipeline stages in more detail using this sample data.
