Projected Field Name

The <projectedFieldName> cannot include a dot (.) in the name.

If the specified <projectedFieldName> already exists in the matching documents, in the result set, the existing fields will return with the $meta values instead of with the stored values.

Projection

The $meta expression can be used in the projection document, as in:

db.collection.find(
   <query>,
   { score: { $meta: "textScore" } }
)

The $meta expression specifies the inclusion of the field to the result set and does not specify the exclusion of the other fields.

The $meta expression can be a part of a projection document that specifies exclusions of other fields or that specifies inclusions of other fields.

The metadata returns information on the processing of the <query> operation. As such, the returned metadata, assigned to the <projectedFieldName>, has no meaning inside a <query> expression; i.e. specifying a condition on the <projectedFieldName> as part of the <query> is similar to specifying a condition on a non-existing field if no field exists in the documents with the <projectedFieldName>.

Sort

The $meta expression can be part of a sort() expression, as in:

db.collection.find(
   <query>,
   { score: { $meta: "textScore" } }
).sort( { score: { $meta: "textScore" } } )

To include a $meta expression in a sort() expression, the same $meta expression, including the <projectedFieldName>, must appear in the projection document. The specified metadata determines the sort order. For example, the "textScore" metadata sorts in descending order.

For additional examples, see Text Search with Additional Query and Sort Expressions.