DATAMONGO-2138 - Typed nested properties

Author: TjeuKayim

Diff for: spring-data-mongodb/src/main/kotlin/org/springframework/data/mongodb/core/query/NestedProperty.kt

@@ -0,0 +1,55 @@
+/*
+ * Copyright 2018 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.springframework.data.mongodb.core.query
+
+import kotlin.reflect.KProperty
+import kotlin.reflect.KProperty1
+
+/**
+ * Refer to a field in an embedded/nested document.
+ * @author Tjeu Kayim
+ * @since 2.2
+ */
+class NestedProperty<T, U>(
+	internal val parent: KProperty<U>,
+	internal val child: KProperty1<U, T>
+) : KProperty<T> by child
+
+/**
+ * Recursively construct field name for a nested property.
+ * @author Tjeu Kayim
+ */
+internal fun nestedFieldName(property: KProperty<*>): String {
+	return when (property) {
+		is NestedProperty<*, *> ->
+			"${nestedFieldName(property.parent)}.${property.child.name}"
+		else -> property.name
+	}
+}
+
+/**
+ * Build nested properties with Property References.
+ * Refer to a field in an embedded/nested document.
+ *
+ * For example, referring to the field "book.author":
+ * ```
+ * Book::author / Author::name isEqualTo "Herman Melville"
+ * ```
+ * @author Tjeu Kayim
+ * @since 2.2
+ */
+operator fun <T, U> KProperty<T>.div(other: KProperty1<T, U>) =
+	NestedProperty(this, other)

Diff for: spring-data-mongodb/src/test/kotlin/org/springframework/data/mongodb/core/query/NestedPropertyTests.kt

@@ -0,0 +1,65 @@
+/*
+ * Copyright 2018 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.springframework.data.mongodb.core.query
+
+import org.assertj.core.api.Assertions.assertThat
+import org.junit.Test
+
+/**
+ * @author Tjeu Kayim
+ */
+class NestedPropertyTests {
+
+	@Test
+	fun `Convert normal KProperty to field name`() {
+
+		val property = nestedFieldName(Book::title)
+
+		assertThat(property).isEqualTo("title")
+	}
+
+	@Test
+	fun `Convert nested KProperty to field name`() {
+
+		val property = nestedFieldName(Book::author / Author::name)
+
+		assertThat(property).isEqualTo("author.name")
+	}
+
+	@Test
+	fun `Convert double nested KProperty to field name`() {
+
+		class Entity(val book: Book)
+
+		val property = nestedFieldName(Entity::book / Book::author / Author::name)
+
+		assertThat(property).isEqualTo("book.author.name")
+	}
+
+	@Test
+	fun `Convert triple nested KProperty to field name`() {
+
+		class Entity(val book: Book)
+		class AnotherEntity(val entity: Entity)
+
+		val property = nestedFieldName(AnotherEntity::entity / Entity::book / Book::author / Author::name)
+
+		assertThat(property).isEqualTo("entity.book.author.name")
+	}
+
+	class Book(val title: String, val author: Author)
+	class Author(val name: String)
+}