Considered new defaults for JPA repository bootstrap

[odrotbohm]

Spring Boot 2.1 exposes a property spring.data.jpa.repositories.bootstrap-mode that can be set to default (default) deferred or lazy. I suggest do change the default value for property to be changed in the following scenarios:

• Change the general default to deferred – it parallelizes the bootstrap of the EntityManagerFactory and delays repository initialization to the end of the ApplicationContext initialization. I.e. there are performance benefits to the startup but the app is the same state as with the current default once it has been started.
• Default to lazy for @SpringBootTest, @DataJpaTest – this leaves all but repositories injected into the tests initialized which gives a bit of a performance boost in both scenarios.

[jnizet]

I wonder if going lazy for SpringBootTest and DataJpaTest is a good idea.

When creating a brand new project using initializr, a single test is typically created: contextLoads.

This test, as far as I understand, is meant to check that the context loads correctly, and thus that the application won't throw any exception once executed.

I understand that this is of course only one test, and that many others should be created, but still: with JPA repositories loaded lazily, this test will pass even though, for example, one of the JPA queries is invalid.

And, if DataJpaTest also uses lazy, if just one of the repositories happens not to be tested and is never injected anywhere, then an invalid JPA query in this repository will go unnoticed in tests.

Being faster is nice, but when it comes to tests, I'd rather have tests that are a tiny bit slower but that detect bugs.

What do you think?

[wilkinsona]

I'm not in favour of any default that increases the risk of deploying something that's broken. Fast startup is all well and good, but I don't think it should be done at the expense of correctness. Other frameworks have made a different choice, and that may turn out to work well for their users, but I think it would be a mistake for us to follow suit purely to speed up startup time or test execution time.

Rather than making @SpringBootTest or @DataJpaTest lazy by default, I'd prefer to add some of the discussion in this blog post to our reference documentation, along with some examples showing how lazy initialization can be enabled in tests (@SpringBootTest(properties="spring.main.lazy-initialization=true") should be all it takes). We could also consider an attribute on the @…Test annotations to make it even easier to opt in.

[ankurbhakta]

What are your thoughts of adding this optimizations as defaults in just spring boot devtools to improve the development experience?

[odrotbohm]

Thanks for the feedback everyone. Very good points included. I guess I've been focussing too much on the how, whereas my actual concern was to make it very easy to make use of these configuration options.

I totally agree that we by no means should change the defaults in a way that currently working scenarios (like the general application bootstrap test that @jnizet described) should start to behave different in a less constraining way.

The proposal for making deferred the default still stands as the end result of the initialization is still equivalent to the current default, it just allows the asynchronous EntityManagerFactory initialization to take most effect possible.

Regarding the lazy initialization, I agree that making it the default for DevTools is a good idea. For the test cases, my primary goal was to avoid spending time on initializing beans that are not required by a particular test. For @Data…Test, there shouldn't be a need to initialize any repositories that are not injected into the test class. The ones injected will be fully initialized on first interaction. This should make practically no difference to the user experience as potential misconfigurations are still detected. Slightly later, but still. In fact, making other repositories lazy by default would result in those tests not fail due to bootstrap errors of unrelated repositories and thus provide a more precise picture of what's wrong exactly.

As far as I can see this is currently needed to lazify repositories for such tests:

@DataJpaTests
@TestPropertySource(properties = "spring.data.jpa.repositories.bootstrap-mode=lazy")
class MyTests { … }

I wonder if this could be shortcutted to an attribute on the @Data…Test annotations and default to lazy with the option for users to opt out of this again.

[wilkinsona]

We're going to:

• Switch the default to deferred for normal running and @SpringBootTest
• Switch to lazy for @Data…Test
• Add an attribute to @Data…Test that uses the BootstrapMode annotation to change the default

[scottfrederick]

• Switch to lazy for @Data…Test
• Add an attribute to @Data…Test that uses the BootstrapMode annotation to change the default

I'm not sure what the ... should mean in the @Data...Test annotations mentioned above, but JPA repositories are the only type of repositories that have a bootstrapMode attribute on their respective @Enable...Repositories annotation in Spring Data, and the only type with a bootstrap-mode property for Spring Boot auto-configuration.

In addition, it is not currently possible to have more than one Spring Data repository configured with BootstrapMode.DEFERRED (see https://jira.spring.io/browse/DATAJPA-1672). Changing the default to DEFERRED for all types of repositories would have the potential to break any application that included more than one Spring Data Repository of any type.

For these two reasons, we should change the default to DEFERRED only for JpaRepositories and LAZY only for @DataJpaTest, leaving the default as DEFAULT for all other types of Repositories.