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