Search by alike() criteria is broken when type alias information is not available [DATAMONGO-2620]

[spring-projects-issues]

Roman Puchkovskiy opened DATAMONGO-2620 and commented

It is possible to configure MappingMongoConverter in such a way that 'class' attribute is not saved to MongoDB. For example, the following setup

MappingContextTypeInformationMapper typeInformationMapper = new MappingContextTypeInformationMapper(
 mappingContext);
DefaultMongoTypeMapper typeMapper = new DefaultMongoTypeMapper(DefaultMongoTypeMapper.DEFAULT_TYPE_KEY,
 singletonList(typeInformationMapper));

MappingMongoConverter converter = new MappingMongoConverter(NoOpDbRefResolver.INSTANCE, mappingContext);
converter.setTypeMapper(typeMapper);

would produce the following behavior: if an entity class is annotated with @TypeAlias, then the corresponding type alias is saved in class attribute to MongoDB, otherwise no such attribute is added.

This setup seems legitimate: one could decide that they do not need class attribute at all if they do not plan to ever use inheritance for some their entity classes.

But this setup makes Criteria.alike(Example) queries useless: they do not find anything. This happens, because DefaultMongoTypeMapper#writeTypeRestrictions() does not check whether restrictedMappedTypes is empty and adds "{'class': {$in: [...]"}} restriction even in such an (empty) case, which produces "{'class': {$in: []"}} which matches nothing as there is simply no class attribute.

This restriction is needed to make sure that only entities of the 'right' type are found. But if we don't have any type alias information, it seems natural to just drop the restriction

---

Affects: 2.2.9 (Moore SR9), 3.0.3 (Neumann SR3)

Referenced from: pull request #884

[spring-projects-issues]

Christoph Strobl commented

Thanks for bringing this to our attention.
If you opt out of having type information written, you may do so as well for the Example by using an untyped one, as outlined in the reference documentation.

Looking at the tests in PR#884 the following should work out of the box.

Criteria alikeCriteria = new Criteria().alike(Example.of(savedPerson, UntypedExampleMatcher.matching()));
List<Person> foundPeople = templateSavingNoTypeInfoInDb.find(new Query(alikeCriteria), Person.class);

[spring-projects-issues]

Roman Puchkovskiy commented

I see, the untyped matched really makes the test pass with the unmodified mapper. Thank you, I overlooked this API feature.

But, on the other hand, does it even make sense to try to make a typed matching when we know that there is no type information available? Also, Example.of(person) does not explicitly state that it will use type-strict check at all times.

Anyway, please let me know about your decision about this. If you feel that the existing behavior is ok, I will close the PR

[spring-projects-issues]

If you would like us to look at this issue, please provide the requested information. If the information is not provided within the next 7 days this issue will be closed.

[spring-projects-issues]

Closing due to lack of requested feedback. If you would like us to look at this issue, please provide the requested information and we will re-open the issue.

[rpuch]

I wonder why I have not received any notification about this issue...

[christophstrobl]

@rpuch Sorry about that! Might be due to the recent Jira to Github issues migration. The automation added a comment to the ticket in Jira but did not (to avoid noise) try to link authors to GH users when moving tickets over.

We'll be addressing this issue by updating the documentation.