Aggregation Pipeline Builder¶

Limitations¶

The $out stage is not available if you are connected to a Data Lake.

Create an Aggregation Pipeline¶

1

Add an aggregation pipeline stage.¶

In the aggregation pipeline pane in the lower-left corner, click the Select... dropdown and select the aggregation pipeline stage to use for the first stage of the pipeline:

2

Fill in the pipeline stage.¶

Fill in your selected stage. If you enable Auto Preview, preview documents update automatically to the right of the stage to reflect the results of your pipeline as it progresses. You can adjust the width of the pipeline stage by dragging its border to the right.

3

Add additional pipeline stages.¶

Click Add Stage to add additional aggregation stages below your last aggregation stage. Repeat steps 1 and 2 for each additional stage.

Note

The toggle to the right of the name of each pipeline stage dictates whether that stage is included in the pipeline. Toggling a pipeline stage also updates the pipeline preview, which reflects whether or not that stage is included.

Example

The following pipeline excludes the first $match stage and only includes the $project stage:

Save a Pipeline¶

You can save a pipeline so that you can find it later. If you load a saved pipeline, you can change it without changing the original saved copy. You can also create a view from your pipeline results.

To save your pipeline:

1. Click the Save button at the top of the pipeline builder.
2. Enter a name for your pipeline.
3. Click Save.

Open a Saved Pipeline¶

1. Click the Folder icon at the top left of the pipeline builder.
2. Hover over the pipeline you want to open and click Open.
3. In the modal, click Open Pipeline.

Set the Documents Limit or Auto Preview Documents¶

Use the toggles at the top of the pipeline builder to set the limit on the number of sampled documents or to enable auto preview.

View or Change Pipeline Settings¶

To view and change pipeline settings:

1. Click the gear icon at the upper right of the pipeline builder to open the Settings panel.

2. Change any of the following pipeline settings.

   Option	Description	Default
   Comment Mode¶	When enabled, adds helper comments to each stage.	Enabled
   Number of Preview Documents¶	Number of documents to show in the preview.	20
   Max Time¶	Cumulative time limit in milliseconds for processing the pipeline. Use this option to limit the waiting time if the pipeline stops responding.	5000
   Limit¶	When Sample Mode is enabled, specifies the number of documents passed to $group, $bucket, and $bucketAuto stages. Lower limits improve pipeline running time, but may miss documents.	100000

3. Click Apply to save changes and close the Settings panel.

Specify Custom Collation¶

Use custom collation to specify language-specific rules for string comparison, such as rules for letter case and accent marks.

To specify a custom collation:

1. Click the Collation button at the top of the pipeline builder.
2. Enter your collation document.

Create a View from Pipeline Results¶

To create a view from your pipeline results:

1. Click the arrow next to the Save button at the top of the pipeline builder.
2. Click Create a View.
3. Enter a name for your view.
4. Click Create.

Compass creates a view from your pipeline results in the same database where the pipeline was created.

Example¶

In this example, you create and run a pipeline for a collection with airline data. You can download this dataset from the following link: air_airlines.json.

For instructions on importing JSON data into your cluster, see mongoimport. This example assumes you have the data in the example.air_airlines namespace.

Create the Pipeline¶

The following pipeline has two aggregation stages: $group and $match.

• The $group stage groups documents by their active status and country. The stage also adds a new flightCount field containing the number of documents in each group.
• The $match stage filters documents to return documents with a flightCount value greater than or equal to 5.

{ "_id" : { "active" : "Y", "country" : "Nigeria" }, "flightCount" : 5 }
{ "_id" : { "active" : "N", "country" : "Switzerland" }, "flightCount" : 46 }
{ "_id" : { "active" : "N", "country" : "Bahrain" }, "flightCount" : 8 }
{ "_id" : { "active" : "N", "country" : "Guinea-Bissau" }, "flightCount" : 8 }
{ "_id" : { "active" : "N", "country" : "Argentina" }, "flightCount" : 14 }
{ "_id" : { "active" : "N", "country" : "Moldova" }, "flightCount" : 17 }
{ "_id" : { "active" : "Y", "country" : "Israel" }, "flightCount" : 6 }
{ "_id" : { "active" : "N", "country" : "Finland" }, "flightCount" : 7 }