DATAMONGO-2596 - Introduce extension to render KProperty/KPropertyPath as property path.

Original pull request: #880.

Author: ydemartino

spring-data-mongodb/src/main/kotlin/org/springframework/data/mongodb/core/query/KPropertyPath.kt

@@ -22,12 +22,17 @@ import kotlin.reflect.KProperty1
  * Abstraction of a property path consisting of [KProperty].
  * @author Tjeu Kayim
  * @author Mark Paluch
+ * @author Yoann de Martino
  * @since 2.2
  */
 class KPropertyPath<T, U>(
 		internal val parent: KProperty<U>,
 		internal val child: KProperty1<U, T>
-) : KProperty<T> by child
+) : KProperty<T> by child {
+	override fun toString(): String {
+		return asString(this)
+	}
+}
 
 /**
  * Recursively construct field name for a nested property.
@@ -45,7 +50,7 @@ internal fun asString(property: KProperty<*>): String {
  * Builds [KPropertyPath] from Property References.
  * Refer to a field in an embedded/nested document.
  *
- * For example, referring to the field "book.author":
+ * For example, referring to the field "author.name":
  * ```
  * Book::author / Author::name isEqualTo "Herman Melville"
  * ```

spring-data-mongodb/src/test/kotlin/org/springframework/data/mongodb/core/query/KPropertyPathTests.kt

@@ -20,6 +20,7 @@ import org.junit.Test
 
 /**
  * @author Tjeu Kayim
+ * @author Yoann de Martino
  */
 class KPropertyPathTests {
 
@@ -60,6 +61,26 @@ class KPropertyPathTests {
 		assertThat(property).isEqualTo("entity.book.author.name")
 	}
 
+	@Test
+	fun `Convert nested KProperty to field name using toString()`() {
+
+		val property = (Book::author / Author::name).toString()
+
+		assertThat(property).isEqualTo("author.name")
+	}
+
+
+	@Test
+	fun `Convert triple nested KProperty to field name using toString()`() {
+
+		class Entity(val book: Book)
+		class AnotherEntity(val entity: Entity)
+
+		val property = (AnotherEntity::entity / Entity::book / Book::author / Author::name).toString()
+
+		assertThat(property).isEqualTo("entity.book.author.name")
+	}
+
 	class Book(val title: String, val author: Author)
 	class Author(val name: String)
 }