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

Now toDocument calls toDocument on items correctly.

Original Pull Request: #883

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

@@ -41,6 +41,7 @@ import org.springframework.util.StringUtils;
  *
  * @author Christoph Strobl
  * @author Mark Paluch
+ * @author Michał Kurcius
  * @since 2.1
  */
 public class TypedJsonSchemaObject extends UntypedJsonSchemaObject {
@@ -1194,7 +1195,7 @@ public class TypedJsonSchemaObject extends UntypedJsonSchemaObject {
 			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

@@ -22,6 +22,7 @@ import static org.springframework.data.mongodb.core.schema.JsonSchemaObject.of;
 import static org.springframework.data.mongodb.test.util.Assertions.*;
 
 import java.util.Arrays;
+import java.util.Collections;
 
 import org.bson.Document;
 import org.junit.Test;
@@ -33,6 +34,7 @@ import org.springframework.data.domain.Range.*;
  *
  * @author Christoph Strobl
  * @author Mark Paluch
+ * @author Michał Kurcius
  */
 public class JsonSchemaObjectUnitTests {
 
@@ -209,6 +211,13 @@ public class JsonSchemaObjectUnitTests {
 				.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() {