Migrating from createQuery() to find() doesn't work as expected

Please ask your question and provide whatever background or supporting information you think might be relevant: Hi @evanchooly, I’m in the process of migrating from v1.6 to v2.0 and I’m having some trouble re-writing queries from createQuery() to find() because of some counter-intuitive behaviour

Code snippets

When using 1.6 the following simple mongo query would work:

               PricingVersion potential = datastore.createQuery(PricingVersion.class).order("-createdAt").get();
               // null check and logging
              return potential;

In 2.0 this becomes:

               return datastore.find(PricingVersion.class)
                               .iterator(new FindOptions()
                                               .sort(descending("createdAt")))
                               .next();

However the MongoCursor throws a NoSuchElementException.

Logs

After some digging in the logs I found that the mongo command has changed from (v1.6):

{"find": "PricingVersion", "sort": {"createdAt": -1}, "limit": 1, "$db": "datahub_v", ... }

to (v2.0):

{"find": "pricingVersion", "filter": {"_t": {"$in": ["PricingVersion"]}}, "sort": {"createdAt": -1}, "$db": "datahub_v", ...}

I would expect {"find": "PricingVersion"}

After reading through the source code I found I could workaround this issue by using find(final String collection, final Class<T> type) from here. My code became

               return datastore.find("PricingVersion", PricingVersion.class)
                               .iterator(new FindOptions()
                                               .sort(descending("createdAt")))
                               .next();

But this still throws a NoSuchElementException…

Here is the mongo request log:

{"find": "PricingVersion", "filter": {"_t": {"$in": ["PricingVersion"]}}, "sort": {"createdAt": -1}, "$db": "datahub_v", ...}

How can I properly retrieve the list of PricingVersions from mongo in morphia v2.0?

Additional info

In the migration to morphia v2.0, a field was removed in the PricingVersion class:

        # deprecated price curve
	@Reference
	@JsonAlias("curves")
	private Map<String, Curve> oldcurves = new HashMap<>();

On top of being deprecated, this field also caused problem in morphia 2.0 because the @ Reference annotation requires Map to have an id.

Is this related to the fact the query above is returning a NoSuchElementExceptionand not the list of pricing versions as expected?

Aside - refactoring

In https://github.com/MorphiaOrg/morphia/blob/master/morphia/src/main/java/dev/morphia/query/MorphiaQuery.java#L62 you might want to change the order of the parameters from

MorphiaQuery(final Datastore datastore, final String collectionName, final Class<T> clazz)

to

MorphiaQuery(final Datastore datastore, final Class<T> clazz, final String collectionName)

to match the overloaded constructor just below which looks like

MorphiaQuery(final Datastore datastore, final Class<T> clazz, final Document query)

It makes it slightly more readable and less confusing when reading this if statement

Thanks for reading this far! 😄

[ppartarr]

I’ll stick to MapperOptions#legacy() for now then. I’ll keep an eye out on the docs and start planning the migration. Thanks for your help! 👍

[evanchooly]

What you’re running in to is, well, two things: a change in the default behavior and lack of sufficient documentation. How are you building your MapperOptions? Are you explicitly building a MapperOptions? In 1.6 dev.morphia.mapping.MapperOptions#builder() was deprecated in favor of dev.morphia.mapping.MapperOptions#legacy() because some defaults were going to change. If you don’t use MapperOptions directly, you’re getting the new defaults automatically.

One of those changes is the ability to set collection/field naming strategies. In the case of collections that is now camelCase which is what you’re seeing. If update your code to use dev.morphia.mapping.MapperOptions#legacy() when creating your Mapper, you’ll get the “correct” class name. You can also use dev.morphia.mapping.MapperOptions#builder() directly and just update the naming strategy to your personal preference.

This is a gap in the migration docs which I’ll update shortly to correct.

And yes, that constructor order is annoyingly inconsistent. 😃