{commons}@data-commons::page$kotlin/extensions.adoc
To retrieve a list of SWCharacter
objects in Java, you would normally write the following:
Flux<SWCharacter> characters = template.query(SWCharacter.class).inTable("star-wars").all()
With Kotlin and the Spring Data extensions, you can instead write the following:
val characters = template.query<SWCharacter>().inTable("star-wars").all()
// or (both are equivalent)
val characters : Flux<SWCharacter> = template.query().inTable("star-wars").all()
As in Java, characters
in Kotlin is strongly typed, but Kotlin’s clever type inference allows for shorter syntax.
Kotlin embraces domain-specific language creation through its language syntax and its extension system.
Spring Data MongoDB ships with a Kotlin Extension for Criteria
using Kotlin property references to build type-safe queries.
Queries using this extension are typically benefit from improved readability.
Most keywords on Criteria
have a matching Kotlin extension, such as inValues
and regex
.
Consider the following example explaining Type-safe Queries:
import org.springframework.data.mongodb.core.query.*
mongoOperations.find<Book>(
Query(Book::title isEqualTo "Moby-Dick") (1)
)
mongoOperations.find<Book>(
Query(titlePredicate = Book::title exists true)
)
mongoOperations.find<Book>(
Query(
Criteria().andOperator(
Book::price gt 5,
Book::price lt 10
))
)
// Binary operators
mongoOperations.find<BinaryMessage>(
Query(BinaryMessage::payload bits { allClear(0b101) }) (2)
)
// Nested Properties (i.e. refer to "book.author")
mongoOperations.find<Book>(
Query(Book::author / Author::name regex "^H") (3)
)
-
isEqualTo()
is an infix extension function with receiver typeKProperty<T>
that returnsCriteria
. -
For bitwise operators, pass a lambda argument where you call one of the methods of
Criteria.BitwiseCriteriaOperators
. -
To construct nested properties, use the
/
character (overloaded operatordiv
).