Exercise 3: Sorting the documents in the aggregation pipeline

In this exercise, you’ll add the third and final stage to the pipeline. The stage is based on the $sort aggregate operator, which lets you sort the documents in the pipeline, based on one or more fields.

To sort the documents in the aggregation pipeline

1. On the IntelliShell tab, ensure that the aggregate statement you updated in the previous exercise is still entered at the command prompt.
2. After the closing curly brace for the second stage, type a comma and insert a new line.
3. On the new line after the second stage, add the following stage to the pipeline:

{ "$sort": { "total": -1 } }

This stage uses the $sort operator to sort the documents in the pipeline based on the values in the total field. The operator expression specifies a value of -1 for the sort order, which means the results will be sorted in descending order, with the highest value first. The aggregate statement should now look like the following code:

db.customers.aggregate(
  [
    { "$match": { "dob": { "$lt": ISODate("1970-01-01T00:00:00.000Z") } } }, 
    { "$group": 
      { "_id": "$address.state", "total": { "$sum": "$transactions" } } },
    { "$sort": { "total": -1 } }
  ]
);

4. On the IntelliShell toolbar, click the Execute button. Studio 3T runs the aggregate statement and displays the results in the lower pane, as shown in the following figure.

Notice that the results are now sorted by the total values, starting with the state with the most transactions and then working down.

5. Leave the IntelliShell tab open and the existing statement in place for the next exercise.