Inconsistent type alias placement in list of classes [DATAMONGO-1509]

[spring-projects-issues]

Tomasz Grabarczyk opened DATAMONGO-1509 and commented

I have the following classes:

@Document
public class TestDocument {
	
	@Id private String id;
	private List<TestClass> testClassList;

	public TestDocument() {
		this.testClassList = null;
	}
	
	public TestDocument(List<TestClass> testClassList) {
		this.testClassList = testClassList;
	}
}

public class TestClass { }

public class TestSubClass extends TestClass {

	private String field;

	public TestSubClass(String field) {
		this.field = field;
	}
}

Now I run the following code:

TestClass testClass = new TestSubClass("value");
mongoTemplate.insert(new TestDocument(Arrays.asList(testClass)));
Query query = Query.query(Criteria.where("testClassList").is(testClass));
TestDocument result = mongoTemplate.findOne(query, TestDocument.class);
System.out.println(result);		// prints: null

I would expect that this query should return the document I inserted at the beginning, but it doesn't. The reason for that is that the TestClass is converted differently when saving document, and differently when creating the query:

Document saved to the database:

"_id" : ObjectId("57fe47fd24474e28ec1db2ed"),
"_class" : "TestDocument",
"testClassList" : [
    {
        "field" : "value",
        "_class" : "TestSubClass"
    }
]

The query:

{ "testClassList" : { "_class" : "TestSubClass" , "field" : "value"}}

I think it shouldn't be like that

---

Affects: 1.10 M1 (Ingalls), 1.9.4 (Hopper SR4)

Issue Links:

• DATAMONGO-1210 Inconsistent property order of _class type hint breaks document equality

Referenced from: pull request #411, and commits e987a85, 987461a, c9573ed, 3c16b4d, 8c50baa, 0ee8789, d6f560d

[spring-projects-issues]

Tomasz Grabarczyk commented

I was able to successfully circumvent this issue by changing DefaultMongoTypeMapper.DBObjectTypeAliasAccessor#writeTypeTo to:

@Override
public void writeTypeTo(DBObject sink, Object alias) {
	if (typeKey == null) return;
	if (sink instanceof BasicDBObject) {
		prependObject((BasicDBObject) sink, typeKey, alias);
	} else {
		sink.put(typeKey, alias);
	}
}


// Puts the given entry (key and object) at the beginning of the given BasicDBObject
private void prependObject(BasicDBObject dbObject, String key, Object object) {
	BasicDBObject objectCopy = new BasicDBObject();
	objectCopy.append(key, object);
	objectCopy.putAll(dbObject.toMap());
	dbObject.clear();
	dbObject.putAll(objectCopy.toMap());
}

but it is probably not the best solution

[spring-projects-issues]

Oliver Drotbohm commented

Maybe I am missing something here but are you saying the query doesn't match if _class appears before field in the query and it's stored the other way around in the document?

[spring-projects-issues]

Tomasz Grabarczyk commented

Yes, the query doesn't match in that case. This behavior is documented in MongoDb docs, which says:

Equality matches on an embedded document require an exact match of the specified <value>, including the field order

[spring-projects-issues]

Christoph Strobl commented

thanks for reporting - yes the order of _class seems to get messed up during the conversion. Will need to have a closer look where that actually happens