DATAMONGO-2613 - Fix single element ArrayJsonSchemaObject to document mapping.

Now toDocument calls toDocument on items correctly.

Original Pull Request: #883

Author: mkurcius

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/schema/TypedJsonSchemaObject.java

@@ -41,6 +41,7 @@
  *
  * @author Christoph Strobl
  * @author Mark Paluch
+ * @author Michał Kurcius
  * @since 2.1
  */
 public class TypedJsonSchemaObject extends UntypedJsonSchemaObject {
@@ -1203,7 +1204,7 @@ public Document toDocument() {
 			Document doc = new Document(super.toDocument());
 
 			if (!CollectionUtils.isEmpty(items)) {
-				doc.append("items", items.size() == 1 ? items.iterator().next()
+				doc.append("items", items.size() == 1 ? items.iterator().next().toDocument()
 						: items.stream().map(JsonSchemaObject::toDocument).collect(Collectors.toList()));
 			}
 

spring-data-mongodb/src/test/java/org/springframework/data/mongodb/core/schema/JsonSchemaObjectUnitTests.java

@@ -41,6 +41,7 @@
  *
  * @author Christoph Strobl
  * @author Mark Paluch
+ * @author Michał Kurcius
  */
 public class JsonSchemaObjectUnitTests {
 
@@ -269,6 +270,13 @@ public void arrayObjectShouldRenderItemsCorrectly() {
 				.append("items", Arrays.asList(new Document("type", "string"), new Document("type", "boolean"))));
 	}
 
+	@Test // DATAMONGO-2613
+	public void arrayObjectShouldRenderItemsCorrectlyAsObjectIfContainsOnlyOneElement() {
+
+		assertThat(array().items(Collections.singletonList(string())).toDocument()).isEqualTo(new Document("type", "array")
+				.append("items", new Document("type", "string")));
+	}
+
 	@Test // DATAMONGO-1835
 	public void arrayObjectShouldRenderMaxItemsCorrectly() {