Hibernate does not load lazy onetone entity attributes with activated batching

[Postremus]

Describe the bug
My entity has a lazy onetoone relationship to a child entity.
Attributes of the child entity are not read. They are kept null.
Eager onetoone work as expected.

After some debugging, I figured out that batching is the problem.
I removed quarkus.hibernate-orm.batch-fetch-size=100 from my configuration, and my child is loaded correctly.

Expected behavior
Attributes of my lazy loaded child onetone entity should get loaded.
Batching should work in all cases.

Actual behavior
Attributes of entities in a OneToOne relationship do not get loaded. They are null.
Any eager loaded onetone gets loaded correctly, with all attributes.

To Reproduce
Steps to reproduce the behavior:

1. Download this reproducer project:
   hibernate-lazy-one-to-one.zip
2. start it in dev mode by running mvn clean compile quarkus:dev inside the hibernate-lazy-one-to-one directory.
3. Go to http://localhost:8080/hello/
4. Set a Break Point at ExampleRepository#findName. And attach the debugger
5. Go to http://localhost:8080/hello/1
6. The debugger should now be inside the findName method.
7. The name is still empty after line 26.
8. Now remove quarkus.hibernate-orm.batch-fetch-size from the application.properties. Do everything again starting from step 3. Name now does get loaded correctly.

Configuration

quarkus.datasource.db-kind=h2
quarkus.datasource.username=sa
quarkus.datasource.jdbc.url=jdbc:h2:mem:test
quarkus.hibernate-orm.database.generation=drop-and-create
quarkus.transaction-manager.default-transaction-timeout=300s
quarkus.hibernate-orm.batch-fetch-size=100

Environment (please complete the following information):

• Output of uname -a or ver:
  MSYS_NT-10.0 NANB7NLNVP2 2.10.0(0.325/5/3) 2018-06-13 23:34 x86_64 Msys
• Quarkus version or git rev:
  1.6.0.Final
• Build tool (ie. output of mvnw --version or gradlew --version):
  Apache Maven 3.6.3 (cecedd343002696d0abb50b32b541b8a6ba2883f)
  Maven home: C:\eclipse\tools\apache-maven\bin..
  Java version: 11.0.7, vendor: Azul Systems, Inc., runtime: C:\eclipse\tools\zulu11.39.15-ca-jdk11.0.7-win_x64
  Default locale: de_DE, platform encoding: Cp1252
  OS name: "windows 10", version: "10.0", arch: "amd64", family: "windows"

[quarkusbot]

/cc @gsmet, @Sanne

[Sanne]

@dreab8 could you check this out please?

[dreab8]

@Sanne sure

[Sanne]

Apparently the bug is triggered when combining Enhanced Proxies with the PADDED or DYNAMIC batch strategies. Quarkus uses the PADDED strategy, while Hibernate ORM upstream by default is using LEGACY for backwards compatibility.

Unfortunately Enhanced Proxies had only been tested in combination with the ORM default, we'll fix this in Hibernate.

[Sanne]

https://hibernate.atlassian.net/browse/HHH-14108