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Add a section about immutable classes persistence in Kotlin refdoc

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Sebastien Deleuze
2017-09-26 00:04:12 +02:00
parent 74120ef00f
commit b85764c7db
1 changed files with 32 additions and 4 deletions
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src/docs/asciidoc/kotlin.adoc
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@@ -353,8 +353,9 @@ functions of Spring beans proxified with CGLIB such as `@Configuration` classes.
Fortunately, Kotlin 1.0.6+ now provides a
https://kotlinlang.org/docs/reference/compiler-plugins.html#kotlin-spring-compiler-plugin[`kotlin-spring`]
plugin that automatically opens classes and their member functions for types
annotated or meta-annotated with one of the following annotations:
plugin, a preconfigured version of `kotlin-allopen` plugin that automatically opens classes
and their member functions for types annotated or meta-annotated with one of the following
annotations:
* `@Component`
* `@Async`
@@ -367,6 +368,33 @@ annotations are meta-annotated with `@Component`.
http://start.spring.io/#!language=kotlin[start.spring.io] enables it by default.
=== Using immutable class instances for persistence
In Kotlin, it is very convenient and a best practice to declare read-only properties within
the primary constructor, as in the following example:
[source,kotlin]
----
class Person(val name: String, val age: Int)
----
But some persistence technologies like JPA require a default constructor, preventing this
kind of design. Fortunately, there is now a workaround for this
https://stackoverflow.com/questions/32038177/kotlin-with-jpa-default-constructor-hell["default constructor hell"]
since Kotlin provides a https://kotlinlang.org/docs/reference/compiler-plugins.html#kotlin-jpa-compiler-plugin[kotlin-jpa]
plugin which generates synthetic no-arg constructor for classes annotated with JPA annotations.
If you need to leverage this kind of mechanism for other persistence technologies, you can
configure https://kotlinlang.org/docs/reference/compiler-plugins.html#how-to-use-no-arg-plugin[kotlin-noarg]
plugin.
[NOTE]
====
As of Kay release train, Spring Data supports Kotlin immutable class instances and should
not require `kotlin-noarg` plugin if the underlying persistence solution allows it
(for example with MongoDB).
====
=== Injecting dependencies
Our recommendation is to try and favor constructor injection with `val` read-only (and non-nullable when possible)
@@ -562,8 +590,8 @@ Spring WebFlux is recommended if one wants to create applications that will deal
long-lived connections, streaming scenarios or simply if one wants to use the web functional
Kotlin DSL.
For other use cases, Spring MVC and its annotation-based programming model is a perfectly
valid and fully supported choice.
For other use cases, especially if you are using blocking technologies like JPA, Spring
MVC and its annotation-based programming model is a perfectly valid and fully supported choice.
[[resources-started]]
== Resources