Fix raw document conversion in Collection like properties.

Along the lines make sure to convert map like structures correctly if they do not come as a Document, eg. cause they got converted to a plain Map in a post load, pre convert event.

Closes #3702
Original pull request: #3704.

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/convert/MappingMongoConverter.java

@@ -1907,8 +1907,20 @@ public class MappingMongoConverter extends AbstractMongoConverter implements App
 			}
 
 			if (typeHint.isMap()) {
+
+				if(ClassUtils.isAssignable(Document.class, typeHint.getType())) {
+					return (S) documentConverter.convert(this, (Bson) source, typeHint);
+				}
+
+				if(source instanceof Bson) {
 					return (S) mapConverter.convert(this, (Bson) source, typeHint);
 				}
+				if(source instanceof Map) {
+					return (S) mapConverter.convert(this, new Document((Map<String,Object>) source), typeHint);
+				}
+
+				throw new IllegalArgumentException(String.format("Expected map like structure but found %s", source.getClass()));
+			}
 
 			if (source instanceof DBRef) {
 				return (S) dbRefConverter.convert(this, (DBRef) source, typeHint);

spring-data-mongodb/src/test/java/org/springframework/data/mongodb/core/convert/MappingMongoConverterUnitTests.java

@@ -2571,6 +2571,38 @@ class MappingMongoConverterUnitTests {
 		assertThat(target.content).isInstanceOf(byte[].class);
 	}
 
+	@Test // GH-3702
+	void readsRawDocument() {
+
+		org.bson.Document source = new org.bson.Document("_id", "id-1").append("raw", new org.bson.Document("simple", 1).append("document", new org.bson.Document("inner-doc", 1)));
+
+		WithRawDocumentProperties target = converter.read(WithRawDocumentProperties.class, source);
+
+		assertThat(target.raw).isInstanceOf(org.bson.Document.class).isEqualTo( new org.bson.Document("simple", 1).append("document", new org.bson.Document("inner-doc", 1)));
+	}
+
+	@Test // GH-3702
+	void readsListOfRawDocument() {
+
+		org.bson.Document source = new org.bson.Document("_id", "id-1").append("listOfRaw", Arrays.asList(new org.bson.Document("simple", 1).append("document", new org.bson.Document("inner-doc", 1))));
+
+		WithRawDocumentProperties target = converter.read(WithRawDocumentProperties.class, source);
+
+		assertThat(target.listOfRaw)
+				.containsExactly(new org.bson.Document("simple", 1).append("document", new org.bson.Document("inner-doc", 1)));
+	}
+
+	@Test // GH-3692
+	void readsMapThatDoesNotComeAsDocument() {
+
+		org.bson.Document source = new org.bson.Document("_id", "id-1").append("mapOfObjects", Collections.singletonMap("simple", 1));
+
+		ClassWithMapProperty target = converter.read(ClassWithMapProperty.class, source);
+
+		assertThat(target.mapOfObjects).containsEntry("simple",1);
+
+	}
+
 	static class GenericType<T> {
 		T content;
 	}
@@ -3229,4 +3261,11 @@ class MappingMongoConverterUnitTests {
 			return null;
 		}
 	}
+
+	static class WithRawDocumentProperties {
+
+		String id;
+		org.bson.Document raw;
+		List<org.bson.Document> listOfRaw;
+	}
 }