Exercise 2: Unwinding an array to create individual documents

In this exercise, you’ll add a stage to the aggregation pipeline that uses the $unwind aggregate operator to deconstruct the interests array in the sales collection.

To unwind the array

1. On the Pipeline tab of the Aggregation Editor, right-click the $match pipeline stage, and then click Add New Stage After Selected Stage.
2. On the new tab, select the $unwind option from the Operator drop-down list. The $unwind operator creates a document for each element in the specified array field. 
3. In the editor window, replace the placeholder text and curly braces with the following code:

{ path: "$interests" }

The $unwind operator requires the path argument, which specifies the field path to the target array. In this case, the target array is the interests field (preceded by a dollar sign).

4. Run the Stage Input and Stage Output tabs. The following figure shows part of the results, as they appear in Table View.

Because the $unwind operator creates a document for every array element in each input document, the output now includes 105 documents, rather than 37. For example, the input data includes a single document with an email value of cnelson7u@umich.edu, but the output data includes four documents with an email value of cnelson7u@umich.edu because the original document contained four elements in the interests array.

5. Click Save on the Aggregation Editor toolbar to save your changes.
6. Leave the Aggregation tab open and the existing statement in place for the next exercise.