Query for "Is Not Null" in MongoDB Using $ne and $exists

How to Query for Non-Null Fields in MongoDB?

To query for documents where a field is not null in MongoDB, you can use the $ne operator, which means "not equal." Alternatively, the $exists operator can be combined with $ne to check both that the field exists and is not null. This is useful when you want only documents with meaningful values in a specific field.

Description:

In MongoDB, querying for fields that are not null helps filter documents to exclude those where a field has a null value. The $ne (not equal) operator is typically used for this purpose, as it matches any value that is not null. For cases where you want to ensure the field is also present, you can combine $exists with $ne for stricter filtering.

Syntax:

There are two common syntaxes to query for "is not null":

Basic syntax with $ne:

{ <field>: { $ne: null } }

Combined syntax with $exists and $ne:

{ : { $ne: null, $exists: true } }

Explanation:

• <field>: The field you are checking for a non-null value.
• $ne: null: Checks that the field value is not equal to null.
• $exists: true: Ensures the field is present in the document.

Example Code:

In this example, we’ll query a users collection to find all documents where the email field is not null and is present in the document.

Code:

// Query the 'users' collection
db.users.find(
  {
    // Find documents where 'email' is not null and exists
    email: {
      // Check that 'email' is not null
      $ne: null,
      // Ensure 'email' field exists in the document
      $exists: true
    }
  }
)

Explanation:

• db.users.find(...)
  This initiates a query in the users collection.
• { email: { $ne: null, $exists: true } }
  The query filters for documents where the email field exists and is not null.
• $ne: null
  $ne checks that the email field does not have a null value.
• $exists: true
  $exists ensures that the email field is present in the document.

MongoDB will return all documents in the users collection where email has a non-null value and exists, filtering out any documents where email is either null or missing entirely.