Neo4jTemplate.DefaultExecutableQuery.getSingleResult() always executes in non-readonly transaction

[mkoertgen]

When activating Neo4jTransactionManager.setValidateExistingTransaction(true) a simple findById() will result in an IllegalStateException. This is due to getSingleResult() always executing in the default transactional-template

https://github.com/spring-projects/spring-data-neo4j/blob/main/src/main/java/org/springframework/data/neo4j/core/Neo4jTemplate.java#L1277

whereas the outer call findById() executes in a readonly-transaction.

https://github.com/spring-projects/spring-data-neo4j/blob/main/src/main/java/org/springframework/data/neo4j/core/Neo4jTemplate.java#L338

How to reproduce:

1. activate transaction validation as described in @michael-simons tips (see below)
2. call findById() on a neo4j-template or -repository

See also

• https://info.michael-simons.eu/2018/09/25/validate-nested-transaction-settings-with-spring-and-spring-boot/
• https://michael-simons.github.io/neo4j-examples-and-tips/validate_transaction_settings.html

[meistermeier]

Thanks for reporting this. Unfortunately in this case, there is -at least from my current perspective- less we can do about this situation.
A while ago we have seen users struggling with multiple database queries getting invoked by the Neo4jTemplate for a single operation. Their code were not running within the same transaction because they did not manually introduce (Spring's) transactional boundaries e.g. by using @Transactional. To get a better user experience and less surprises, we decided to introduce also the transaction template in the Neo4jTemplate as a good will.
What you have discovered is somehow a consequence of this behaviour. While the findById flow should definitely be read-only, the getSingleResult could be part of a data-manipulating query because there are other flows that can lead here without a transaction in the first place.
But as I have said in the beginning, this is was just a first analysis from my side. I will keep the issue open to investigate this deeper and see if we could come up with a solution for this situation.

[mkoertgen]

Hi @meistermeier,

Thanks for the prompt response. From what I can see at first glance, it looks promising to first fix the call-scopes in Neo4jTemplate directly. One way to go about this, would be to allow the transaction to be optionally passed down to getSingleResult() via method injection. If you don't mind I would submit a PR for this.

[meistermeier]

If you want to do this in a PR, I am happy to have a look.
Please keep in mind that we want to avoid breaking API changes at all cost. This means that you cannot just add a parameter to getSingleResult() but need to find a way around this. Maybe a sibling method with less visibility that accepts this from the internal calls in Neo4jTemplate only. (Just thinking loud here).

Personal addition: When you filed your PR, please don't expect a quick response within the next two weeks because I will be on vacation.

[mkoertgen]

Sounds good to me, thx. 👍

[mkoertgen]

@meistermeier Have a look at #2962 at your convenience. Happy to update if you have any remarks.