$exists

The $exists operator in MongoDB is one of the essential element operators used to filter documents in queries. This operator allows you to search documents in a collection based on the presence or absence of a field, regardless of its value.

Syntax

{ field: { $exists: <boolean> } }

Here, <boolean> can be either true or false. If true, then it filters the documents containing the specified field, and if false, it filters the documents not containing the specified field.

Examples

• Find all documents where the field "author" exists:

db.books.find({ author: { $exists: true } });

• Find all documents where the field "publisher" does not exist:

db.books.find({ publisher: { $exists: false } });

Usage with Embedded Documents

$exists also works perfectly with embedded documents or arrays when searching for the presence or absence of specific fields.

Example:

Find all documents where the field "address.city" is present.

db.users.find({ 'address.city': { $exists: true } });

Note

Keep in mind that $exists checks for both the presence of a field and null values since they represent the existence of a field with no value. If you want to search for fields with non-null values, you can use a combination of $exists and $ne (not equal to) operator.

Example:

Find all documents where the field "edition" exists and has a non-null value.

db.books.find({ edition: { $exists: true, $ne: null } });

That's all you need to know about $exists in MongoDB! Happy querying!