For the most recent version of the reference documentation, see our MongoDB Java Driver documentation site.
- Builders
- Projections
Projections
The Projections
class provides static factory methods for all the MongoDB
projection opererators. Each method returns an instance of the Bson
type, which can in turn
be passed to any method that expects a projection.
For brevity, you may choose to import the methods of the Projections
class statically:
import static com.mongodb.client.model.Projections.*;
All the examples below assume this static import.
Inclusion
By default, all fields of each document are projected. To specify the inclusion of one or more fields (which implicitly excludes all
other fields except _id
), use the include
method.
This example includes the quantity
field and (implicitly) the _id
field:
include("quantity")
This example includes the quantity
and totalAmount
fields and (implicitly) the _id
field:
include("quantity", "totalAmount")
Exclusion
To specify the exclusion of one or more fields (which implicitly includes all other fields), use the exclude
method.
This example excludes the quantity
field:
exclude("quantity")
This example excludes the quantity
and totalAmount
fields:
exclude("quantity", "totalAmount")
Exclusion of _id
To specify the exclusion of the _id
field, use the excludeId
method:
excludeId()
which is just shorthand for:
exclude("_id")
Array Element Match with a Supplied Filter
To specify a projection that includes only the first element of an array that matches a supplied query filter (the
elemMatch operator), use the elemMatch
method that takes a
field name and a filter.
This example projects the first element of the orders
array where the quantity
field is greater that 3
:
elemMatch("orders", Filters.gt("quantity", 3))
Array Element Match with an Implicit Filter
To specify a projection that includes only the first element of an array that matches the filter supplied as part of the query (the
positional $ operator), use the elemMatch
method that takes
just a field name.
This example projects the first element of the orders
array that matches the query filter:
elemMatch("orders")
Slice
To project a slice of an array, use one of the slice
methods.
This example projects the first 7
elements of the tags
array:
slice("tags", 7)
This example skips the first 2
elements of the tags
array and projects the next 5
:
slice("tags", 2, 5)
Text Score
To specify a projection of the score of a $text
query,
use the metaTextScore
method to specify the name of the projected field.
This example projects the text score as the value of the score
field:
metaTextScore("score")
Combining Projections
To combine multiple projections, use the fields
method.
This example includes the quantity
and totalAmount
fields and excludes the _id
field:
fields(include("quantity", "totalAmount"), excludeId())