$meta¶

On this page

Behaviors
Examples

$meta¶

2.6 新版功能.

The $meta projection operator returns for each matching document the metadata (e.g. "textScore") associated with the query.

A $meta expression has the following syntax:

{ $meta: <metaDataKeyword> }

The $meta expression can specify the following keyword as the <metaDataKeyword>:

Keyword	Description	Sort Order
`"textScore"`	Returns the score associated with the corresponding `$text` query for each matching document. The text score signifies how well the document matched the search term or terms. If not used in conjunction with a `$text` query, returns a score of 0.	Descending

Behaviors¶

The $meta expression can be a part of the projection document as well as a sort() expression as:

{ <projectedFieldName>: { $meta: "textScore" } }

db.collection.find() operations on views do not support $meta projection operator.

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.

Examples¶

For examples of "textScore" projections and sorts, see $text.

← $elemMatch (projection) $slice (projection) →