From a530629d976ff2612b99c4d054cf3853641cff64 Mon Sep 17 00:00:00 2001
From: Oliver Gierke <info@olivergierke.de>
Date: Mon, 30 Jul 2012 15:39:22 +0200
Subject: [PATCH] DATAMONGO-497 - Fixed reading of empty collections.

Reading an empty collection always returned a HashSet assuming the returned value would be converted into the assigned properties value later on. However the method should rather return the correct type already which we do now by invoking the potential conversion.
---
 .../core/convert/MappingMongoConverter.java   |  5 +++--
 .../MappingMongoConverterUnitTests.java       | 21 +++++++++++++++++++
 2 files changed, 24 insertions(+), 2 deletions(-)

diff --git a/spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/convert/MappingMongoConverter.java b/spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/convert/MappingMongoConverter.java
index f6452dde9..3dcfb9dfe 100644
--- a/spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/convert/MappingMongoConverter.java
+++ b/spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/convert/MappingMongoConverter.java
@@ -720,11 +720,12 @@ public class MappingMongoConverter extends AbstractMongoConverter implements App
 
 		Assert.notNull(targetType);
 
+		Class<?> collectionType = targetType.getType();
+
 		if (sourceValue.isEmpty()) {
-			return new HashSet<Object>();
+			return getPotentiallyConvertedSimpleRead(new HashSet<Object>(), collectionType);
 		}
 
-		Class<?> collectionType = targetType.getType();
 		collectionType = Collection.class.isAssignableFrom(collectionType) ? collectionType : List.class;
 
 		Collection<Object> items = targetType.getType().isArray() ? new ArrayList<Object>() : CollectionFactory
diff --git a/spring-data-mongodb/src/test/java/org/springframework/data/mongodb/core/convert/MappingMongoConverterUnitTests.java b/spring-data-mongodb/src/test/java/org/springframework/data/mongodb/core/convert/MappingMongoConverterUnitTests.java
index e2acf9a6a..18d231a6e 100644
--- a/spring-data-mongodb/src/test/java/org/springframework/data/mongodb/core/convert/MappingMongoConverterUnitTests.java
+++ b/spring-data-mongodb/src/test/java/org/springframework/data/mongodb/core/convert/MappingMongoConverterUnitTests.java
@@ -1252,6 +1252,18 @@ public class MappingMongoConverterUnitTests {
 		assertThat(values, is(arrayWithSize(2)));
 	}
 
+	/**
+	 * @see DATAMONGO-497
+	 */
+	@Test
+	public void readsEmptyCollectionIntoConstructorCorrectly() {
+
+		DBObject source = new BasicDBObject("attributes", new BasicDBList());
+
+		TypWithCollectionConstructor result = converter.read(TypWithCollectionConstructor.class, source);
+		assertThat(result.attributes, is(notNullValue()));
+	}
+
 	private static void assertSyntheticFieldValueOf(Object target, Object expected) {
 
 		for (int i = 0; i < 10; i++) {
@@ -1440,6 +1452,15 @@ public class MappingMongoConverterUnitTests {
 		Long innerId;
 	}
 
+	static class TypWithCollectionConstructor {
+
+		List<Attribute> attributes;
+
+		public TypWithCollectionConstructor(List<Attribute> attributes) {
+			this.attributes = attributes;
+		}
+	}
+
 	private class LocalDateToDateConverter implements Converter<LocalDate, Date> {
 
 		public Date convert(LocalDate source) {