Field¶

interface Field<in Root, out Type>

High-level, typesafe pointer to a specific field in a document.

This type may refer to fields nested in children documents or arrays. Instances are generally used to refer to a MongoDB field we want to read or update, when writing requests.

Type safety¶

This type is responsible for ensuring type safety:

class User(
    val _id: ObjectId,
    val profile: Profile,
    val friends: List<Friend>,
)

class Profile(
    val name: String,
)

class Friend(
    val name: String,
    val age: Int,
)

// Refer to the user's id
println(User::_id.field)

// Refer to the user's name
println(User::profile / Profile::name)

// Refer to the name of the second friend
println(User::friends[1] / Friend::name)

Some of the functions of the DSL may be available only when FieldDsl is in scope. All operator scopes provided by this library should bring it into scope automatically.

For example, when writing a filter, methods from this interface are automatically available:

collection.find {
    User::profile / Profile::name eq "Thibault Lognaise"
}

To bypass type-safety, and refer to arbitrary fields without declaring them first, see unsafe.

Parameters¶

Root: The type of the document in which this field is in.
Type: The type of the value stored by this field.

Types¶

`Companion`¶

object Companion

Properties¶

path¶

@LowLevelApi



abstract val path: Path

Low-level representation of this field's path.

Functions¶

toBsonPath¶

@LowLevelApi



fun Path.toBsonPath(): BsonPath

Converts this MongoDB Path to a BsonPath.

BsonPath is an implementation of RFC9535 JSONPath. See its documentation for more information.

fun Field<*, *>.toBsonPath(): BsonPath

Converts this MongoDB Field to a BsonPath.

BsonPath is an implementation of RFC9535 JSONPath. See its documentation for more information.

BsonPath can be useful to access elements from an arbitrary BSON document, for example, after a projection.

Example¶

data class User(
    val _id: ObjectId,
    val profile: Profile,
)

data class Profile(
    val name: String,
)

val fieldName = (User::profile / Profile::name).toBsonPath()

val bson: Bson = …
val name = bson at fieldName

See also

select: Select multiple values.
selectFirst: Select the first value.
at: Select the first value, as an infix operator.