$size

Compatibility

You can use $size for deployments hosted in the following environments:

• MongoDB Atlas: The fully managed service for MongoDB deployments in the cloud

• MongoDB Enterprise: The subscription-based, self-managed version of MongoDB

• MongoDB Community: The source-available, free-to-use, and self-managed version of MongoDB

Consider the following examples:

db.collection.find( { field: { $size: 2 } } );

This query returns all documents in collection where field is an array with 2 elements. For instance, the above expression will return { field: [ red, green ] } and { field: [ apple, lime ] } but not { field: fruit } or { field: [ orange, lemon, grapefruit ] }. To match fields with only one element within an array use $size with a value of 1, as follows:

db.collection.find( { field: { $size: 1 } } );

$size does not accept ranges of values. To select documents based on fields with different numbers of elements, create a counter field that you increment when you add elements to a field.

Queries cannot use indexes for the $size portion of a query, although the other portions of a query can use indexes if applicable.

Additional Examples

For additional examples on querying arrays, see:

• Query an Array

• Query an Array of Embedded Documents

For additional examples on querying, see Query Documents.