Other MongoDB hints and tips

Example filter queries for target collections

When configuring subsetting in a MongoDB workspace, you can filter a target collections using either a percentage or a filter query.

For example, a customers collection contains the customer first name, last name, and membership status, as shown in the following sample records:

{
	"FirstName": "John",
	"LastName": "Smith",
	"Member": true
}
{
	"FirstName": "Jane",
	"LastName": "Doe",
	"Member": false
}

To filter the records to only include members, the filter query would be:

{"Member":true}

As another example, the following filter query checks whether the eighth character in an object ID called _id is equal to 9.

{
    $expr: {
        $eq: [
        { $substr: [ { $toString: "$_id" }, 8, 1 ] },
        "9"
        ]
        }
    }
}