How to Run `$unionWith` with an Atlas Search `$search` Query

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Create the Atlas Search Indexes

Run $unionWith with $search to Search the Collections

Starting in v6.0, the MongoDB $unionWith aggregation stage supports $search inside the $unionWith pipeline option. Using $unionWith, you can combine $search results from multiple collections in the same database in the result set.

This tutorial demonstrates how to run a $unionWith query with $search against the companies and inspections collections in the sample_training database. It takes you through the following steps:

Set up an Atlas Search index with dynamic mappings for the companies and inspections collections in the sample_training database.
Run $unionWith query with $search to perform a union of companies with mobile in their name from the companies collection with companies with same or similar business name in the inspections collection.

Before you begin, ensure that your Atlas cluster meets the requirements described in the Prerequisites.

Note

To run a $unionWith query with $search, your cluster must run MongoDB v6.0 or higher.

Create the Atlas Search Indexes

In this section, you will create an Atlas Search index named default on all the fields in the companies collection in the sample_training database. You will create another Atlas Search index named default on all the fields in the inspections collection in the sample_training database. You must perform the following steps for each collection.

Navigate to the Atlas Search page for your project.

If it isn't already displayed, select the organization that contains your desired project from the Organizations menu in the navigation bar.
If it isn't already displayed, select your desired project from the Projects menu in the navigation bar.
Click your cluster's name.
Click the Search tab.

Create an index.

For your first index, click Create Search Index.
For subsequent indexes, click Create Index.

Select a Configuration Method and click Next.

For a guided experience, select Visual Editor.
To edit the raw index definition, select JSON Editor.

Enter the Index Name, and set the Database and Collection.

In the Index Name field, enter default.
Note
If you name your index default, you don't need to specify an index parameter when using the $search pipeline stage. Otherwise, you must specify the index name using the index parameter.
In the Database and Collection section, find the sample_training database, and select the collection.
- To create an index for the companies collection, select companies.
- To create an index for the inspections collection, select inspections.

Specify an index definition.

The following index definition dynamically indexes the fields of supported types in the collection. You can use the Visual Editor or the JSON Editor in the Atlas user interface to create the index.

Click Create Search Index.

Close the You're All Set! Modal Window.

A modal window displays to let you know your index is building. Click the Close button.

Wait for the index to finish building.

The index should take about one minute to build. While it is building, the Status column reads Build in Progress. When it is finished building, the Status column reads Active.

Run `$unionWith` with `$search` to Search the Collections

In this section, you will connect to your Atlas cluster and run the sample query against the indexed collections in the sample_training database.

Connect to your cluster in `mongosh`.

Open mongosh in a terminal window and connect to your cluster. For detailed instructions on connecting, see Connect via mongosh.

Switch to the `sample_training` database.

Run the following command at mongosh prompt:

use sample_training

switched to db sample_training

Run the following `$unionWith` with an Atlas Search `$search` query.

The following queries search both the companies and inspections collections for the term mobile in the name and business_name fields respectively. The query uses the following stages:

$search to search for companies that include mobile in the name.
$unionWith to do the following:
- Use $search stage in the sub-pipeline to search for inspections of companies that include mobile in the name.
- Perform a union of documents from the companies and documents from the inspections collections.
$set stage to add a new field named source that identifies the collection of the output documents.
$limit stage to limit the output to 3 results from each collection.
$project stage to:
- Include only the specified fields in the results.
- Add a field named score.

← How to Run $lookup with an Atlas Search $search Query How to Run Atlas Search Queries Against Objects in Arrays →

Note

Create the Atlas Search Indexes

Navigate to the Atlas Search page for your project.

Create an index.

Select a Configuration Method and click Next.

Enter the Index Name, and set the Database and Collection.

Note

Specify an index definition.

Click Create Search Index.

Close the You're All Set! Modal Window.

Wait for the index to finish building.

Run $unionWith with $search to Search the Collections

Connect to your cluster in mongosh.

Switch to the sample_training database.

Run the following $unionWith with an Atlas Search $search query.

Run `$unionWith` with `$search` to Search the Collections

Connect to your cluster in `mongosh`.

Switch to the `sample_training` database.

Run the following `$unionWith` with an Atlas Search `$search` query.