I tried to set up multiple datasource with 2 datasources include

1. datasource1 which is annotated with @Primary.
2. datasource2.

then query data by using findAll()(that belong to @Primary datasource, datasource1) it work without any error.

but got the following error when I called the the findAll() method that belong to datasource2

Resolved [org.springframework.http.converter.HttpMessageNotWritableException: Could not write JSON: failed to lazily initialize a collection of role: com.example.linewebhookjava.entity.datasource2.Projects2.itemUpdates: could not initialize proxy - no Session]

I have tried change @ElementCollection(fetch = FetchType.LAZY) to @ElementCollection(fetch = FetchType.EAGER) in Projects2 entity.

or

place this spring.jpa.properties.hibernate.enable_lazy_load_no_trans=true into application.properties

the error was gone.
But the point is why it is fail on datasource2 (secondary datasource).

Conclusion, calling findAll() that belong to datasource with @Primary work fine , but didn’t work on findAll() of the secondary datasource.

Additionally, I have tried swapping @Primary annotation with another datasource.

(Here’s my code with sql and docker-compose.yml
https://github.com/annopud/line-webhook-java/tree/no_session)