Field¶
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)
// _id
// Refer to the user's name
println(User::profile / Profile::name)
// profile.name
// Refer to the name of the second friend
println(User::friends[1] / Friend::name)
// friends.1.name
An instance of FieldDsl is required in scope to call these methods. All KtMongo commands automatically bring an instance of FieldDsl into scope.
For example, when writing a filter, methods from this interface are automatically available:
To bypass type-safety, and refer to arbitrary fields without declaring them first, see unsafe.
Type 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
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.
unsafeCast¶
open fun <O> unsafeCast(): Field<Root, O>
Overwrites the represented type of this field.
This method can be useful to bypass type checks, it tells KtMongo to treat the field as if it were of some other type.